Add VmType intermediate representation for types (#1838)

.idea/inspectionProfiles/Project_Default.xml

@@ -12,6 +12,7 @@
       <option name="REPORT_FIELDS" value="true" />
     </inspection_tool>
     <inspection_tool class="ClassCanBeRecord" enabled="false" level="WEAK WARNING" enabled_by_default="false" />
+    <inspection_tool class="ClassEscapesItsScope" enabled="false" level="WARNING" enabled_by_default="false" />
     <inspection_tool class="CustomRegExpInspection" enabled="true" level="WARNING" enabled_by_default="true">
       <option name="myConfigurations">
         <list>

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/SubscriptNode.java

@@ -124,7 +124,7 @@ public abstract class SubscriptNode extends BinaryExpressionNode {
       CompilerDirectives.transferToInterpreter();
       throw exceptionBuilder()
           .evalError(
-              "operatorNotDefined2", getShortName(), reference.exportType(), VmUtils.getClass(key))
+              "operatorNotDefined2", getShortName(), reference.getType(), VmUtils.getClass(key))
           .withProgramValue("Left operand", reference)
           .withProgramValue("Right operand", key)
           .withHint(getReferenceHint(reference, err, key))

pkl-core/src/main/java/org/pkl/core/ast/expression/literal/CheckIsAnnotationClassNode.java

@@ -41,9 +41,9 @@ public final class CheckIsAnnotationClassNode extends ExpressionNode {
       typeNode = insert(unresolvedTypeNode.execute(frame));
       unresolvedTypeNode = null;
     }
-    var clazz = typeNode.getVmClass();
+    var clazz = typeNode.getType().getVmClass();
     if (clazz != null && clazz.isSubclassOf(BaseModule.getAnnotationClass())) {
-      return typeNode.getVmClass();
+      return clazz;
     }
 
     CompilerDirectives.transferToInterpreter();

pkl-core/src/main/java/org/pkl/core/ast/expression/member/AbstractInferParentNode.java

@@ -57,7 +57,7 @@ public abstract class AbstractInferParentNode extends ExpressionNode {
     }
 
     // try to produce a more specific error message than "cannotInstantiateType"
-    var clazz = typeNode.getVmClass();
+    var clazz = typeNode.getType().getVmClass();
     if (clazz != null) {
       VmUtils.checkIsInstantiable(clazz, typeNode);
     }

pkl-core/src/main/java/org/pkl/core/ast/expression/member/ReadPropertyNode.java

@@ -24,7 +24,6 @@ import com.oracle.truffle.api.nodes.IndirectCallNode;
 import com.oracle.truffle.api.nodes.NodeInfo;
 import com.oracle.truffle.api.source.SourceSection;
 import org.jspecify.annotations.Nullable;
-import org.pkl.core.PType;
 import org.pkl.core.ast.ExpressionNode;
 import org.pkl.core.ast.MemberLookupMode;
 import org.pkl.core.ast.member.ClassProperty;
@@ -77,7 +76,7 @@ public abstract class ReadPropertyNode extends ExpressionNode {
       case DEFAULT_MEMBER ->
           ErrorMessages.create(
               "cannotReferenceDefaultProperty",
-              ((PType.Class) err.getType()).getPClass().getSimpleName());
+              ((VmType.ClassType) err.getType()).getVmClass().getSimpleName());
       case EXTERNAL_CLASS ->
           ErrorMessages.create(
               "cannotReferencePropertyInExternalClass", propertyName, err.getType());
@@ -92,7 +91,7 @@ public abstract class ReadPropertyNode extends ExpressionNode {
     } catch (VmReferenceAccessError err) {
       CompilerDirectives.transferToInterpreter();
       throw exceptionBuilder()
-          .evalError("cannotFindPropertyInObjectNoHint", propertyName, receiver.exportType())
+          .evalError("cannotFindPropertyInObjectNoHint", propertyName, receiver.getType())
           .withHint(getReferenceErrorHint(receiver, err))
           .build();
     }

pkl-core/src/main/java/org/pkl/core/ast/member/ClassNode.java

@@ -129,7 +129,7 @@ public final class ClassNode extends ExpressionNode {
     try {
       if (unresolvedSupertypeNode != null) {
         var supertypeNode = unresolvedSupertypeNode.execute(frame);
-        var superclass = supertypeNode.getVmClass();
+        var superclass = supertypeNode.getType().getVmClass();
 
         checkSupertype(supertypeNode, superclass);
         cachedClass.initSupertype(supertypeNode, superclass);

pkl-core/src/main/java/org/pkl/core/ast/member/FunctionNode.java

@@ -31,6 +31,7 @@ import org.pkl.core.ast.ExpressionNode;
 import org.pkl.core.ast.VmModifier;
 import org.pkl.core.ast.type.TypeNode;
 import org.pkl.core.runtime.*;
+import org.pkl.core.runtime.VmType.UnknownType;
 import org.pkl.core.util.CollectionUtils;
 import org.pkl.core.util.Pair;
 
@@ -86,6 +87,10 @@ public final class FunctionNode extends RegularMemberNode {
     return parameterTypeNodes[idx];
   }
 
+  public VmType getReturnType() {
+    return returnTypeNode == null ? UnknownType.INSTANCE : returnTypeNode.getType();
+  }
+
   public @Nullable TypeNode getReturnTypeNode() {
     return returnTypeNode;
   }

pkl-core/src/main/java/org/pkl/core/ast/type/UnresolvedTypeNode.java

@@ -198,13 +198,13 @@ public abstract class UnresolvedTypeNode extends PklNode {
             case "Int16":
               return new Int16TypeAliasTypeNode();
             case "UInt16":
-              return new UIntTypeAliasTypeNode(alias, 0x000000000000FFFFL);
+              return new IntMaskSlotTypeNode(alias, 0x000000000000FFFFL);
             case "Int32":
               return new Int32TypeAliasTypeNode();
             case "UInt32":
-              return new UIntTypeAliasTypeNode(alias, 0x00000000FFFFFFFFL);
+              return new IntMaskSlotTypeNode(alias, 0x00000000FFFFFFFFL);
             case "UInt":
-              return new UIntTypeAliasTypeNode(alias, 0x7FFFFFFFFFFFFFFFL);
+              return new IntMaskSlotTypeNode(alias, 0x7FFFFFFFFFFFFFFFL);
           }
         }
 

pkl-core/src/main/java/org/pkl/core/ast/type/VmTypeMismatchException.java

@@ -23,7 +23,6 @@ import com.oracle.truffle.api.source.SourceSection;
 import java.util.*;
 import java.util.stream.Collectors;
 import org.jspecify.annotations.Nullable;
-import org.pkl.core.PType;
 import org.pkl.core.StackFrame;
 import org.pkl.core.ValueFormatter;
 import org.pkl.core.ast.type.TypeNode.UnionTypeNode;
@@ -95,6 +94,7 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
 
       assert expectedType instanceof VmClass
           || expectedType instanceof VmTypeAlias
+          || expectedType instanceof VmType
           || expectedType instanceof String // string literal type
           || expectedType instanceof Set; // union of string literal types
 
@@ -153,13 +153,11 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
         }
       }
 
+      var valueType =
+          actualValue instanceof VmReference ref ? ref.getType() : VmUtils.getClass(actualValue);
+
       builder
-          .append(
-              ErrorMessages.createIndented(
-                  "typeMismatch",
-                  indent,
-                  renderedType,
-                  VmUtils.getClass(actualValue).toPklString()))
+          .append(ErrorMessages.createIndented("typeMismatch", indent, renderedType, valueType))
           .append("\n")
           .append(indent)
           .append("Value: ")
@@ -183,10 +181,10 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
       renderedExpected = "Class<" + expectedClass.toPklString() + ">";
     }
 
-    public ClassType(SourceSection sourceSection, VmClass actualClass, PType expectedType) {
+    public ClassType(SourceSection sourceSection, VmClass actualClass, VmType expectedType) {
       super(sourceSection, actualClass);
       this.expectedClass = null;
-      renderedExpected = "Class<" + expectedType + ">";
+      renderedExpected = expectedType.toString();
     }
 
     @Override
@@ -400,44 +398,4 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
       return false;
     }
   }
-
-  public static final class Reference extends VmTypeMismatchException {
-
-    private final PType expectedDomainType;
-    private final PType expectedReferentType;
-
-    public Reference(
-        SourceSection sourceSection,
-        VmReference actualValue,
-        PType expectedDomainType,
-        PType expectedReferentType) {
-      super(sourceSection, actualValue);
-      this.expectedDomainType = expectedDomainType;
-      this.expectedReferentType = expectedReferentType;
-    }
-
-    @Override
-    public void buildMessage(
-        AnsiStringBuilder builder, String indent, boolean withPowerAssertions) {
-      builder
-          .append(
-              ErrorMessages.createIndented(
-                  "typeMismatch",
-                  indent,
-                  new PType.Class(
-                      RefModule.getReferenceClass().export(),
-                      expectedDomainType,
-                      expectedReferentType),
-                  ((VmReference) actualValue).exportType()))
-          .append("\n")
-          .append(indent)
-          .append("Value: ")
-          .append(VmValueRenderer.singleLine(80 - indent.length()).render(actualValue));
-    }
-
-    @Override
-    protected Boolean hasHint() {
-      return false;
-    }
-  }
 }

pkl-core/src/main/java/org/pkl/core/runtime/CommandSpecParser.java

@@ -25,6 +25,7 @@ import java.net.URI;
 import java.net.URISyntaxException;
 import java.nio.file.Path;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
@@ -175,12 +176,12 @@ public final class CommandSpecParser {
     }
     if (!(optionsTypeNode instanceof TypeNode.UserClassTypeNode node)) {
       throw exceptionBuilder()
-          .withSourceSection(optionsTypeNode.getSourceSection())
+          .withSourceSection(optionsPropertyTypeNode.getSourceSection())
           .evalError(
               "commandOptionsTypeNotClass", optionsTypeNode.getSourceSection().getCharacters())
           .build();
     }
-    var clazz = node.getVmClass();
+    var clazz = ((VmType.ClassType) node.getType()).getVmClass();
     if (clazz.isAbstract()) {
       throw exceptionBuilder()
           .withSourceSection(clazz.getHeaderSection())
@@ -308,14 +309,14 @@ public final class CommandSpecParser {
 
     // assert type is Boolean
     var typeInfo = resolveType(prop);
-    if (!(typeInfo.getFirst() instanceof TypeNode.BooleanTypeNode)) {
+    if (typeInfo.getFirst().getVmClass() != BaseModule.getBooleanClass()) {
       throw exceptionBuilder()
           .withSourceSection(prop.getHeaderSection())
           .evalError(
               "commandFlagInvalidType",
               prop.getName(),
               "BooleanFlag",
-              typeInfo.getFirst().getSourceSection().getCharacters(),
+              typeInfo.getFirst().toString(),
               "Boolean")
           .build();
     }
@@ -342,7 +343,7 @@ public final class CommandSpecParser {
               "commandFlagInvalidType",
               prop.getName(),
               "CountedFlag",
-              typeInfo.getFirst().getSourceSection().getCharacters(),
+              typeInfo.getFirst().toString(),
               "Int")
           .build();
     }
@@ -385,10 +386,10 @@ public final class CommandSpecParser {
   }
 
   /** Unwrap nullables, constraints, and aliases and return Pair(underlying type, is nullable) */
-  private Pair<TypeNode, Boolean> resolveType(ClassProperty prop) {
+  private Pair<VmType, Boolean> resolveType(ClassProperty prop) {
     var propertyTypeNode = prop.getTypeNode();
     if (propertyTypeNode != null) {
-      return resolveType(propertyTypeNode.getTypeNode());
+      return resolveType(propertyTypeNode.getTypeNode().getType());
     }
     throw exceptionBuilder()
         .withSourceSection(prop.getHeaderSection())
@@ -397,23 +398,23 @@ public final class CommandSpecParser {
   }
 
   /** Unwrap nullables, constraints, and aliases and return Pair(underlying type, is nullable) */
-  private Pair<TypeNode, Boolean> resolveType(TypeNode typeNode) {
+  private Pair<VmType, Boolean> resolveType(VmType type) {
     var isNullable = false;
     while (true) {
-      if (typeNode instanceof TypeNode.NullableTypeNode nullableTypeNode) {
+      if (type instanceof VmType.NullableType nullableType) {
         isNullable = true;
-        typeNode = nullableTypeNode.getElementTypeNode();
-      } else if (typeNode instanceof TypeNode.ConstrainedTypeNode constrainedTypeNode) {
-        typeNode = constrainedTypeNode.getChildTypeNode();
-      } else if (typeNode instanceof TypeNode.TypeAliasTypeNode typeAliasTypeNode) {
-        if (typeAliasTypeNode.getVmTypeAlias() == BaseModule.getCharTypeAlias()) break;
-        typeNode = typeAliasTypeNode.getAliasedTypeNode();
+        type = nullableType.getElementType();
+      } else if (type instanceof VmType.ConstrainedType constrainedType) {
+        type = constrainedType.getBaseType();
+      } else if (type instanceof VmType.AliasType aliasType) {
+        if (aliasType.getVmTypeAlias() == BaseModule.getCharTypeAlias()) break;
+        type = aliasType.getAliasedType();
       } else {
         break;
       }
     }
 
-    return Pair.of(typeNode, isNullable);
+    return Pair.of(type, isNullable);
   }
 
   // This sigil used to indicate that an option has a default value that is a non-constant expr.
@@ -447,10 +448,12 @@ public final class CommandSpecParser {
         // wrapped by a nullable, no default value
         return null;
       }
-      if (resolved.getFirst() instanceof TypeNode.UnionOfStringLiteralsTypeNode union
-          && union.getUnionDefault() != null) {
-        return union.getUnionDefault();
-      } else if (resolved.getFirst() instanceof TypeNode.StringLiteralTypeNode literal) {
+      if (resolved.getFirst() instanceof VmType.UnionType union
+          && union.getDefaultIndex() != -1
+          && union.isUnionOfStringLiterals()) {
+        return ((VmType.StringLiteralType) union.getElementTypes()[union.getDefaultIndex()])
+            .getLiteral();
+      } else if (resolved.getFirst() instanceof VmType.StringLiteralType literal) {
         return literal.getLiteral();
       }
     }
@@ -509,130 +512,151 @@ public final class CommandSpecParser {
 
     public OptionBehavior resolve(ClassProperty prop, boolean requireExplicitDefault) {
       var resolved = resolveType(prop);
-      var typeNode = resolved.getFirst();
+      var type = resolved.getFirst();
       isNullable = resolved.getSecond();
       defaultValue = CommandSpecParser.this.getDefaultValue(prop, requireExplicitDefault);
 
-      resolve(prop, typeNode);
+      resolve(prop, type);
       return this;
     }
 
-    private void resolve(ClassProperty prop, TypeNode typeNode) {
-      if (resolvePrimitive(typeNode)) {
+    private void resolve(ClassProperty prop, VmType type) {
+      if (resolvePrimitive(type)) {
         return;
       }
-      if (typeNode instanceof TypeNode.ListingTypeNode listingTypeNode) {
-        handleElement(listingTypeNode.getValueTypeNode(), prop);
-        if (multiple == null) multiple = true;
-        if (all == null)
-          all =
-              !multiple
-                  ? this::allChooseLast
-                  : (values, workingDirUri) -> {
-                    if (values.isEmpty()) return null;
-                    var builder = new VmObjectBuilder();
-                    values.forEach(builder::addElement);
-                    return builder.toListing();
-                  };
-      } else if (typeNode instanceof TypeNode.MappingTypeNode mappingTypeNode) {
-        assert mappingTypeNode.getKeyTypeNode() != null;
-        handleEntry(mappingTypeNode.getKeyTypeNode(), mappingTypeNode.getValueTypeNode(), prop);
-        if (multiple == null) multiple = true;
-        if (all == null)
-          all =
-              !multiple
-                  ? this::allChooseLast
-                  : (values, workingDirUri) -> {
-                    if (values.isEmpty()) return null;
-                    var builder = new VmObjectBuilder();
-                    values.forEach(
-                        (entry) ->
-                            builder.addEntry(
-                                ((VmPair) entry).getFirst(), ((VmPair) entry).getSecond()));
-                    return builder.toMapping();
-                  };
-      } else if (typeNode instanceof TypeNode.ListTypeNode listTypeNode) {
-        handleElement(listTypeNode.getElementTypeNode(), prop);
-        if (multiple == null) multiple = true;
-        if (all == null)
-          all =
-              !multiple
-                  ? this::allChooseLast
-                  : (values, workingDirUri) -> values.isEmpty() ? null : VmList.create(values);
-      } else if (typeNode instanceof TypeNode.SetTypeNode setTypeNode) {
-        handleElement(setTypeNode.getElementTypeNode(), prop);
-        if (multiple == null) multiple = true;
-        if (all == null)
-          all =
-              !multiple
-                  ? this::allChooseLast
-                  : (values, workingDirUri) -> values.isEmpty() ? null : VmSet.create(values);
-      } else if (typeNode instanceof TypeNode.MapTypeNode mapTypeNode) {
-        handleEntry(mapTypeNode.getKeyTypeNode(), mapTypeNode.getValueTypeNode(), prop);
-        if (multiple == null) multiple = true;
-        if (all == null)
-          all =
-              !multiple
-                  ? this::allChooseLast
-                  : (values, workingDirUri) -> {
-                    if (values.isEmpty()) return null;
-                    var builder = VmMap.builder();
-                    values.forEach(
-                        (entry) ->
-                            builder.add(((VmPair) entry).getFirst(), ((VmPair) entry).getSecond()));
-                    return builder.build();
-                  };
-      } else if (typeNode instanceof TypeNode.PairTypeNode pairTypeNode) {
-        handleEntry(pairTypeNode.getFirstTypeNode(), pairTypeNode.getSecondTypeNode(), prop);
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-      } else if (typeNode instanceof TypeNode.FinalClassTypeNode finalClassTypeNode
-          && (finalClassTypeNode.getVmClass() == BaseModule.getListingClass()
-              || finalClassTypeNode.getVmClass() == BaseModule.getMappingClass()
-              || finalClassTypeNode.getVmClass() == BaseModule.getListClass()
-              || finalClassTypeNode.getVmClass() == BaseModule.getSetClass()
-              || finalClassTypeNode.getVmClass() == BaseModule.getMapClass()
-              || finalClassTypeNode.getVmClass() == BaseModule.getPairClass())) {
-        // if a supported type is provided without type arguments
-        throw exceptionBuilder()
-            .withSourceSection(prop.getHeaderSection())
-            .evalError(
-                "commandOptionUnsupportedType",
-                prop.getName(),
-                "",
-                typeNode.getSourceSection().getCharacters())
-            .withHint(
-                finalClassTypeNode.getVmClass().getSimpleName()
-                    + " options must provide "
-                    + switch (finalClassTypeNode.getVmClass().getTypeParameterCount()) {
-                      case 1 -> "one type argument.";
-                      case 2 -> "two type arguments.";
-                      default -> throw PklBugException.unreachableCode();
-                    })
-            .build();
-      } else if (each == null && all == null) {
+      if (type instanceof VmType.ClassType ct) {
+        if (ct.getVmClass() == BaseModule.getListingClass()) {
+          handleElement(prop, ct);
+          if (multiple == null) {
+            multiple = true;
+          }
+          if (all == null) {
+            all =
+                !multiple
+                    ? this::allChooseLast
+                    : (values, workingDirUri) -> {
+                      if (values.isEmpty()) return null;
+                      var builder = new VmObjectBuilder();
+                      values.forEach(builder::addElement);
+                      return builder.toListing();
+                    };
+          }
+        } else if (ct.getVmClass() == BaseModule.getMappingClass()) {
+          handleEntry(prop, ct);
+          if (multiple == null) {
+            multiple = true;
+          }
+          if (all == null) {
+            all =
+                !multiple
+                    ? this::allChooseLast
+                    : (values, workingDirUri) -> {
+                      if (values.isEmpty()) return null;
+                      var builder = new VmObjectBuilder();
+                      values.forEach(
+                          (entry) ->
+                              builder.addEntry(
+                                  ((VmPair) entry).getFirst(), ((VmPair) entry).getSecond()));
+                      return builder.toMapping();
+                    };
+          }
+        } else if (ct.getVmClass() == BaseModule.getListClass()) {
+          handleElement(prop, ct);
+          if (multiple == null) {
+            multiple = true;
+          }
+          if (all == null) {
+            all =
+                !multiple
+                    ? this::allChooseLast
+                    : (values, workingDirUri) -> values.isEmpty() ? null : VmList.create(values);
+          }
+        } else if (ct.getVmClass() == BaseModule.getSetClass()) {
+          handleElement(prop, ct);
+          if (multiple == null) {
+            multiple = true;
+          }
+          if (all == null) {
+            all =
+                !multiple
+                    ? this::allChooseLast
+                    : (values, workingDirUri) -> values.isEmpty() ? null : VmSet.create(values);
+          }
+        } else if (ct.getVmClass() == BaseModule.getMapClass()) {
+          handleEntry(prop, ct);
+          if (multiple == null) {
+            multiple = true;
+          }
+          if (all == null) {
+            all =
+                !multiple
+                    ? this::allChooseLast
+                    : (values, workingDirUri) -> {
+                      if (values.isEmpty()) return null;
+                      var builder = VmMap.builder();
+                      values.forEach(
+                          (entry) ->
+                              builder.add(
+                                  ((VmPair) entry).getFirst(), ((VmPair) entry).getSecond()));
+                      return builder.build();
+                    };
+          }
+        } else if (ct.getVmClass() == BaseModule.getPairClass()) {
+          handleEntry(prop, ct);
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+        }
+      }
+
+      if (each == null && all == null) {
         // if another type and no transform functions are provided, that's an error
-        throw exceptionBuilder()
-            .withSourceSection(prop.getHeaderSection())
-            .evalError(
-                "commandOptionUnsupportedType",
-                prop.getName(),
-                "",
-                typeNode.getSourceSection().getCharacters())
-            .withHint("Use a supported type or define a transformEach and/or transformAll function")
-            .build();
+        throw unsupportedOptionNoTransform(prop, type);
       } else {
         // if we have at least one transform then allow the type and fill in reasonable defaults
-        if (each == null) each = (rawValue, workingDirUri) -> rawValue;
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_VALUE;
+        if (each == null) {
+          each = (rawValue, workingDirUri) -> rawValue;
+        }
+        if (all == null) {
+          all = this::allChooseLast;
+        }
+        if (multiple == null) {
+          multiple = false;
+        }
+        if (metavar == null) {
+          metavar = METAVAR_VALUE;
+        }
       }
     }
 
+    private VmException unsupportedOptionTypeArguments(ClassProperty prop, VmType.ClassType type) {
+      var typeArgCountText =
+          switch (type.getVmClass().getTypeParameterCount()) {
+            case 1 -> "one type argument.";
+            case 2 -> "two type arguments.";
+            default -> throw PklBugException.unreachableCode();
+          };
+      return exceptionBuilder()
+          .withSourceSection(prop.getHeaderSection())
+          .evalError("commandOptionUnsupportedType", prop.getName(), "", type.toString())
+          .withHint(type.getVmClass().getSimpleName() + " options must provide " + typeArgCountText)
+          .build();
+    }
+
+    private VmException unsupportedOptionNoTransform(ClassProperty prop, VmType type) {
+      return exceptionBuilder()
+          .withSourceSection(prop.getHeaderSection())
+          .evalError("commandOptionUnsupportedType", prop.getName(), "", type.toString())
+          .withHint("Use a supported type or define a transformEach and/or transformAll function")
+          .build();
+    }
+
     private OptionBehavior resolveTypeArgument(
-        ClassProperty prop, TypeNode typeNode, String typeArgumentName) {
-      if (resolvePrimitive(typeNode)) {
+        ClassProperty prop, VmType type, String typeArgumentName) {
+      if (resolvePrimitive(type)) {
         return this;
       }
 
@@ -644,7 +668,7 @@ public final class CommandSpecParser {
                 "commandOptionUnsupportedType",
                 prop.getName(),
                 typeArgumentName + " ",
-                typeNode.getSourceSection().getCharacters())
+                type.toString())
             .withHint("Use a supported type or define a transformEach and/or transformAll function")
             .build();
       } else if (metavar == null) {
@@ -656,138 +680,252 @@ public final class CommandSpecParser {
       return this;
     }
 
-    private boolean resolvePrimitive(TypeNode typeNode) {
-      if (typeNode instanceof TypeNode.NumberTypeNode) {
-        if (each == null)
-          each =
-              (rawValue, workingDirUri) -> {
-                try {
-                  return Long.parseLong(rawValue);
-                } catch (NumberFormatException e) {
+    private boolean resolvePrimitive(VmType type) {
+      if (type instanceof VmType.ClassType ct) {
+        if (ct.getVmClass() == BaseModule.getNumberClass()) {
+          if (each == null) {
+            each =
+                (rawValue, workingDirUri) -> {
+                  try {
+                    return Long.parseLong(rawValue);
+                  } catch (NumberFormatException e) {
+                    try {
+                      return Double.parseDouble(rawValue);
+                    } catch (NumberFormatException e2) {
+                      throw BadValue.invalid(rawValue, METAVAR_NUMBER);
+                    }
+                  }
+                };
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_NUMBER;
+          }
+          return true;
+        } else if (ct.getVmClass() == BaseModule.getFloatClass()) {
+          if (each == null) {
+            each =
+                (rawValue, workingDirUri) -> {
                   try {
                     return Double.parseDouble(rawValue);
-                  } catch (NumberFormatException e2) {
-                    throw BadValue.invalid(rawValue, METAVAR_NUMBER);
+                  } catch (NumberFormatException e) {
+                    throw BadValue.invalid(rawValue, METAVAR_FLOAT);
                   }
-                }
-              };
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_NUMBER;
-        return true;
-      } else if (typeNode instanceof TypeNode.FloatTypeNode) {
-        if (each == null)
-          each =
-              (rawValue, workingDirUri) -> {
-                try {
-                  return Double.parseDouble(rawValue);
-                } catch (NumberFormatException e) {
-                  throw BadValue.invalid(rawValue, METAVAR_FLOAT);
-                }
-              };
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_FLOAT;
-        return true;
-      } else if (typeNode instanceof TypeNode.IntTypeNode) {
-        if (each == null) each = eachLong(Long.MIN_VALUE, Long.MAX_VALUE, METAVAR_INT);
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_INT;
-        return true;
-      } else if (typeNode instanceof TypeNode.Int8TypeAliasTypeNode) {
-        if (each == null) each = eachLong(Byte.MIN_VALUE, Byte.MAX_VALUE, METAVAR_INT8);
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_INT8;
-        return true;
-      } else if (typeNode instanceof TypeNode.Int16TypeAliasTypeNode) {
-        if (each == null) each = eachLong(Short.MIN_VALUE, Short.MAX_VALUE, METAVAR_INT16);
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_INT16;
-        return true;
-      } else if (typeNode instanceof TypeNode.Int32TypeAliasTypeNode) {
-        if (each == null) each = eachLong(Integer.MIN_VALUE, Integer.MAX_VALUE, METAVAR_INT32);
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_INT32;
-        return true;
-      } else if (typeNode instanceof TypeNode.UIntTypeAliasTypeNode uIntTypeAliasTypeNode) {
-        var mask = uIntTypeAliasTypeNode.getMask();
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (mask == 0x000000000000FFFFL) {
-          if (each == null) each = eachLong(0, 0x000000000000FFFFL, METAVAR_UINT16);
-          if (metavar == null) metavar = METAVAR_UINT16;
-        } else if (mask == 0x00000000FFFFFFFFL) {
-          if (each == null) each = eachLong(0, 0x00000000FFFFFFFFL, METAVAR_UINT32);
-          if (metavar == null) metavar = METAVAR_UINT32;
-        } else {
-          if (each == null) each = eachLong(0, Long.MAX_VALUE, METAVAR_UINT);
-          if (metavar == null) metavar = METAVAR_UINT;
+                };
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_FLOAT;
+          }
+          return true;
+        } else if (ct.getVmClass() == BaseModule.getIntClass()) {
+          if (each == null) {
+            each = eachLong(Long.MIN_VALUE, Long.MAX_VALUE, METAVAR_INT);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_INT;
+          }
+          return true;
+        } else if (ct.getVmClass() == BaseModule.getBooleanClass()) {
+          if (each == null) {
+            each =
+                (rawValue, workingDirUri) -> {
+                  var value = rawValue.toLowerCase(Locale.ROOT);
+                  if (TRUE_VALUES.contains(value)) {
+                    return true;
+                  } else if (FALSE_VALUES.contains(value)) {
+                    return false;
+                  }
+                  throw BadValue.invalid(rawValue, "boolean");
+                };
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_BOOLEAN;
+          }
+          return true;
+        } else if (ct.getVmClass() == BaseModule.getStringClass()) {
+          if (each == null) {
+            each = (rawValue, workingDirUri) -> rawValue;
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_STRING;
+          }
+          return true;
         }
-        return true;
-      } else if (typeNode instanceof TypeNode.UInt8TypeAliasTypeNode) {
-        if (each == null) each = eachLong(0, 0x00000000000000FFL, METAVAR_UINT8);
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_UINT8;
-        return true;
-      } else if (typeNode instanceof TypeNode.BooleanTypeNode) {
-        if (each == null)
+      } else if (type instanceof VmType.AliasType at) {
+        if (at.getVmTypeAlias() == BaseModule.getInt8TypeAlias()) {
+          if (each == null) {
+            each = eachLong(Byte.MIN_VALUE, Byte.MAX_VALUE, METAVAR_INT8);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_INT8;
+          }
+          return true;
+        } else if (at.getVmTypeAlias() == BaseModule.getInt16TypeAlias()) {
+          if (each == null) {
+            each = eachLong(Short.MIN_VALUE, Short.MAX_VALUE, METAVAR_INT16);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_INT16;
+          }
+          return true;
+        } else if (at.getVmTypeAlias() == BaseModule.getInt32TypeAlias()) {
+          if (each == null) {
+            each = eachLong(Integer.MIN_VALUE, Integer.MAX_VALUE, METAVAR_INT32);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_INT32;
+          }
+          return true;
+        } else if (at.getVmTypeAlias() == BaseModule.getUInt8TypeAlias()) {
+          if (each == null) {
+            each = eachLong(0, 0x00000000000000FFL, METAVAR_UINT8);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_UINT8;
+          }
+          return true;
+        } else if (at.getVmTypeAlias() == BaseModule.getUInt16TypeAlias()) {
+          if (each == null) {
+            each = eachLong(0, 0x000000000000FFFFL, METAVAR_UINT16);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_UINT16;
+          }
+        } else if (at.getVmTypeAlias() == BaseModule.getUInt32TypeAlias()) {
+          if (each == null) {
+            each = eachLong(0, 0x00000000FFFFFFFFL, METAVAR_UINT32);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_UINT32;
+          }
+        } else if (at.getVmTypeAlias() == BaseModule.getUIntTypeAlias()) {
+          if (each == null) {
+            each = eachLong(0, Long.MAX_VALUE, METAVAR_UINT);
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_UINT;
+          }
+        } else if (at.getVmTypeAlias() == BaseModule.getCharTypeAlias()) {
+          if (each == null) {
+            each =
+                (rawValue, workingDirUri) -> {
+                  if (rawValue.length() != 1) throw BadValue.invalid(rawValue, METAVAR_CHAR);
+                  return rawValue;
+                };
+          }
+          if (all == null) {
+            all = this::allChooseLast;
+          }
+          if (multiple == null) {
+            multiple = false;
+          }
+          if (metavar == null) {
+            metavar = METAVAR_CHAR;
+          }
+          return true;
+        }
+      } else if (type instanceof VmType.UnionType ut && ut.isUnionOfStringLiterals()) {
+        var choices =
+            Arrays.stream(ut.getElementTypes())
+                .map(it -> ((VmType.StringLiteralType) it).getLiteral())
+                .toList();
+        var choiceSet = new HashSet<>(choices);
+        if (each == null) {
           each =
               (rawValue, workingDirUri) -> {
-                var value = rawValue.toLowerCase(Locale.ROOT);
-                if (TRUE_VALUES.contains(value)) {
-                  return true;
-                } else if (FALSE_VALUES.contains(value)) {
-                  return false;
-                }
-                throw BadValue.invalid(rawValue, "boolean");
-              };
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_BOOLEAN;
-        return true;
-      } else if (typeNode instanceof TypeNode.StringTypeNode) {
-        if (each == null) each = (rawValue, workingDirUri) -> rawValue;
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_STRING;
-        return true;
-      } else if (typeNode instanceof TypeNode.TypeAliasTypeNode typeAliasTypeNode
-          && typeAliasTypeNode.getVmTypeAlias() == BaseModule.getCharTypeAlias()) {
-        if (each == null)
-          each =
-              (rawValue, workingDirUri) -> {
-                if (rawValue.length() != 1) throw BadValue.invalid(rawValue, METAVAR_CHAR);
-                return rawValue;
-              };
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = METAVAR_CHAR;
-        return true;
-      } else if (typeNode
-          instanceof TypeNode.UnionOfStringLiteralsTypeNode unionOfStringLiteralsTypeNode) {
-        var choices = unionOfStringLiteralsTypeNode.getStringLiterals().stream().sorted().toList();
-        if (each == null)
-          each =
-              (rawValue, workingDirUri) -> {
-                if (!unionOfStringLiteralsTypeNode.getStringLiterals().contains(rawValue)) {
+                if (!choiceSet.contains(rawValue)) {
                   throw BadValue.invalidChoice(rawValue, choices);
                 }
                 return rawValue;
               };
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = "[" + String.join(", ", choices) + "]";
-        if (completionCandidates == null)
-          completionCandidates = new Fixed(unionOfStringLiteralsTypeNode.getStringLiterals());
+        }
+        if (all == null) {
+          all = this::allChooseLast;
+        }
+        if (multiple == null) {
+          multiple = false;
+        }
+        if (metavar == null) {
+          metavar = "[" + String.join(", ", choices) + "]";
+        }
+        if (completionCandidates == null) {
+          completionCandidates = new Fixed(choiceSet);
+        }
         return true;
-      } else if (typeNode instanceof TypeNode.StringLiteralTypeNode stringLiteralTypeNode) {
-        var choice = stringLiteralTypeNode.getLiteral();
-        if (each == null)
+      } else if (type instanceof VmType.StringLiteralType slt) {
+        var choice = slt.getLiteral();
+        if (each == null) {
           each =
               (rawValue, workingDirUri) -> {
                 if (!rawValue.equals(choice)) {
@@ -795,10 +933,19 @@ public final class CommandSpecParser {
                 }
                 return rawValue;
               };
-        if (all == null) all = this::allChooseLast;
-        if (multiple == null) multiple = false;
-        if (metavar == null) metavar = "[" + choice + "]";
-        if (completionCandidates == null) completionCandidates = new Fixed(Set.of(choice));
+        }
+        if (all == null) {
+          all = this::allChooseLast;
+        }
+        if (multiple == null) {
+          multiple = false;
+        }
+        if (metavar == null) {
+          metavar = "[" + choice + "]";
+        }
+        if (completionCandidates == null) {
+          completionCandidates = new Fixed(Set.of(choice));
+        }
         return true;
       }
       return false;
@@ -823,7 +970,10 @@ public final class CommandSpecParser {
     private static final Set<String> FALSE_VALUES = Set.of("false", "f", "0", "no", "n", "off");
 
     /** Sets each and metavar if they're not set */
-    private void handleElement(TypeNode valueType, ClassProperty prop) {
+    private void handleElement(ClassProperty prop, VmType.ClassType type) {
+      if (!type.isParametric()) throw unsupportedOptionTypeArguments(prop, type);
+      var valueType = type.getTypeArguments()[0];
+
       if (each != null && metavar != null) return;
       var transformValue =
           new OptionBehavior(each, all, multiple, metavar, completionCandidates)
@@ -833,7 +983,11 @@ public final class CommandSpecParser {
     }
 
     /** Sets each and metavar if they're not set */
-    private void handleEntry(TypeNode keyType, TypeNode valueType, ClassProperty prop) {
+    private void handleEntry(ClassProperty prop, VmType.ClassType type) {
+      if (!type.isParametric()) throw unsupportedOptionTypeArguments(prop, type);
+      var keyType = type.getTypeArguments()[0];
+      var valueType = type.getTypeArguments()[1];
+
       if (each != null && metavar != null) return;
       var transformKey =
           new OptionBehavior(each, all, multiple, metavar, completionCandidates)
@@ -841,7 +995,7 @@ public final class CommandSpecParser {
       var transformValue =
           new OptionBehavior(each, all, multiple, metavar, completionCandidates)
               .resolveTypeArgument(prop, resolveType(valueType).getFirst(), "value");
-      if (each == null)
+      if (each == null) {
         each =
             (rawValue, workingDirUri) -> {
               var split = rawValue.split("=", 2);
@@ -852,7 +1006,10 @@ public final class CommandSpecParser {
                   transformKey.getEach().apply(split[0], workingDirUri),
                   transformValue.getEach().apply(split[1], workingDirUri));
             };
-      if (metavar == null) metavar = transformKey.getMetavar() + "=" + transformValue.getMetavar();
+      }
+      if (metavar == null) {
+        metavar = transformKey.getMetavar() + "=" + transformValue.getMetavar();
+      }
     }
 
     private @Nullable Object allChooseLast(List<Object> values, URI workingDirUri) {

pkl-core/src/main/java/org/pkl/core/runtime/MirrorFactories.java

@@ -223,7 +223,7 @@ public final class MirrorFactories {
         .addTypedProperty(
             "referent",
             typeNode -> {
-              var clazz = typeNode.getVmClass();
+              var clazz = typeNode.getType().getVmClass();
               assert clazz != null;
               return clazz.getMirror();
             })
@@ -232,11 +232,7 @@ public final class MirrorFactories {
     typeAliasTypeFactory
         .addTypedProperty(
             "referent",
-            typeNode -> {
-              var alias = typeNode.getVmTypeAlias();
-              assert alias != null;
-              return alias.getMirror();
-            })
+            typeNode -> ((VmType.AliasType) typeNode.getType()).getVmTypeAlias().getMirror())
         .addListProperty("typeArguments", TypeNode::getTypeArgumentMirrors);
 
     declaredTypeFactory
@@ -251,7 +247,8 @@ public final class MirrorFactories {
         .addListProperty("parameterTypes", Pair::getFirst)
         .addTypedProperty("returnType", Pair::getSecond);
 
-    stringLiteralTypeFactory.addStringProperty("value", StringLiteralTypeNode::getLiteral);
+    stringLiteralTypeFactory.addStringProperty(
+        "value", typeNode -> ((VmType.StringLiteralType) typeNode.getType()).getLiteral());
 
     stringLiteralTypeFactory2.addStringProperty("value", Property.identity());
 

pkl-core/src/main/java/org/pkl/core/runtime/VmClass.java

@@ -244,10 +244,15 @@ public final class VmClass extends VmValue {
     checkAbstractMethods();
   }
 
+  @TruffleBoundary
   public int getTypeParameterCount() {
     return typeParameters.size();
   }
 
+  public List<TypeParameter> getTypeParameters() {
+    return typeParameters;
+  }
+
   /**
    * Returns the property with the given name declared in this class, or {@code null} if no such
    * property was found. Does return local properties.
@@ -298,6 +303,13 @@ public final class VmClass extends VmValue {
     return (VmTyped) module;
   }
 
+  public VmClass getModuleClass() {
+    if (classInfo.isModuleClass()) return this;
+    var module = prototype.getEnclosingOwner();
+    assert module != null;
+    return module.getVmClass();
+  }
+
   public VmTyped getModuleMirror() {
     return getModule().getModuleInfo().getMirror(getModule());
   }
@@ -393,6 +405,11 @@ public final class VmClass extends VmValue {
     return superclass;
   }
 
+  public @Nullable VmType getSupertype() {
+    if (supertypeNode == null) return null;
+    return supertypeNode.getType();
+  }
+
   @Override
   public VmTyped getPrototype() {
     return prototype;
@@ -752,7 +769,7 @@ public final class VmClass extends VmValue {
     return getDisplayName();
   }
 
-  private UnmodifiableEconomicMap<Identifier, ClassProperty> getAllProperties() {
+  public UnmodifiableEconomicMap<Identifier, ClassProperty> getAllProperties() {
     synchronized (allPropertiesLock) {
       if (__allProperties == null) {
         // can't do this in ClassNode because it requires a fully initialized inheritance hierarchy

pkl-core/src/main/java/org/pkl/core/runtime/VmListingOrMapping.java

@@ -133,6 +133,6 @@ public abstract class VmListingOrMapping extends VmObject {
     if (typeCastNode == null) {
       return false;
     }
-    return typeCastNode.getTypeNode().isEquivalentTo(typeNode);
+    return typeCastNode.getTypeNode().getType().equals(typeNode.getType());
   }
 }

pkl-core/src/main/java/org/pkl/core/runtime/VmReference.java

@@ -18,7 +18,7 @@ package org.pkl.core.runtime;
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.nodes.DirectCallNode;
 import java.util.ArrayList;
-import java.util.Collections;
+import java.util.Arrays;
 import java.util.Comparator;
 import java.util.HashSet;
 import java.util.List;
@@ -27,12 +27,11 @@ import java.util.function.BiConsumer;
 import java.util.function.Supplier;
 import org.jspecify.annotations.Nullable;
 import org.pkl.core.Composite;
-import org.pkl.core.PClass;
-import org.pkl.core.PClassInfo;
-import org.pkl.core.PType;
-import org.pkl.core.PklBugException;
 import org.pkl.core.Reference;
-import org.pkl.core.TypeAlias;
+import org.pkl.core.runtime.VmType.NonFinalModuleType;
+import org.pkl.core.runtime.VmType.NonFinalThisType;
+import org.pkl.core.runtime.VmType.NothingType;
+import org.pkl.core.runtime.VmType.UnknownType;
 import org.pkl.core.util.paguro.RrbTree;
 import org.pkl.core.util.paguro.RrbTree.ImRrbt;
 
@@ -41,10 +40,12 @@ public final class VmReference extends VmValue {
   private final VmTyped domain;
   private final Object data;
   private final ImRrbt<VmTyped> path;
-  // candidate types can only be: PType.Class, PType.Alias (only preservedAliasTypes),
-  // PType.StringLiteral, PType.UNKNOWN, PType.Function, PType.TypeVariable, or PType.Union
+  // candidate types can only be: VmType.ClassType, VmType.AliasType (only preservedAliasTypes),
+  // VmType.StringLiteralType, VmType.Unknown.INSTANCE, VmType.FunctionType,
+  // VmType.TypeVariableTybe, or
+  // VmType.UnionType
   // (containing only the previous; flattened)
-  private final PType referentType;
+  private final VmType referentType;
 
   private boolean forced = false;
 
@@ -55,12 +56,15 @@ public final class VmReference extends VmValue {
         .toTyped(RefModule.getAccessClass());
   }
 
-  @TruffleBoundary
   public VmReference(VmTyped domain, VmClass clazz, Object data) {
-    this(domain, data, RrbTree.empty(), normalizeTypes(new PType.Class(clazz.export())));
+    this(
+        domain,
+        data,
+        RrbTree.empty(),
+        normalizeTypes(new VmType.ClassType(clazz), clazz, clazz.getModuleClass()));
   }
 
-  public VmReference(VmTyped domain, Object data, ImRrbt<VmTyped> path, PType referentType) {
+  public VmReference(VmTyped domain, Object data, ImRrbt<VmTyped> path, VmType referentType) {
     this.domain = domain;
     this.data = data;
     this.referentType = referentType;
@@ -79,7 +83,7 @@ public final class VmReference extends VmValue {
     return path;
   }
 
-  public PType getReferentType() {
+  public VmType getReferentType() {
     return referentType;
   }
 
@@ -88,71 +92,67 @@ public final class VmReference extends VmValue {
   // * transforming T? into T|Null
   // * dereferencing aliases (except for well-known stdlib alias types)
   // * flattening unions
-  // * drop PType.Function and PType.TypeVariable
-  private static PType normalizeTypes(
-      PType type, @Nullable PType thisClass, @Nullable PType moduleClass) {
-    var types = new HashSet<PType>();
-    normalizeTypes(type, types, thisClass, moduleClass);
+  // * replace VmType.ModuleType with appropriate VmType.ClassType
+  // * drop VmType.FunctionType and VmType.TypeVariableType
+  @TruffleBoundary
+  private static VmType normalizeTypes(VmType type, VmClass thisClass, VmClass moduleClass) {
+    var types = new HashSet<VmType>();
+    normalizeTypes(type, thisClass, moduleClass, types);
     return minimizeTypes(types);
   }
 
-  private static PType normalizeTypes(PType type) {
-    return normalizeTypes(type, null, null);
-  }
-
-  private static PType minimizeTypes(Set<PType> types) {
+  private static VmType minimizeTypes(Set<VmType> types) {
     if (types.size() == 1) return types.iterator().next();
     // optimization: unknown allows all references, erase all candidates to only unknown
-    if (types.contains(PType.UNKNOWN)) return PType.UNKNOWN;
+    if (types.contains(UnknownType.INSTANCE)) return UnknownType.INSTANCE;
     // optimization: All allows all references, erase all candidates to only All
-    if (containsClass(types, BaseModule.getAnyClass().export()))
-      return new PType.Class(BaseModule.getAnyClass().export());
-    var typesList = new ArrayList<>(types);
-    typesList.sort(Comparator.comparing(Object::toString));
-    return new PType.Union(typesList);
+    if (containsClass(types, BaseModule.getAnyClass())) {
+      return new VmType.ClassType(BaseModule.getAnyClass());
+    }
+    var typeArray = types.toArray(new VmType[0]);
+    Arrays.sort(typeArray, Comparator.comparing(Object::toString));
+    return new VmType.UnionType(-1, typeArray);
   }
 
   private static void normalizeTypes(
-      PType type, Set<PType> result, @Nullable PType thisClass, @Nullable PType moduleClass) {
-    if (type == PType.UNKNOWN || type == PType.NOTHING || type instanceof PType.StringLiteral) {
+      VmType type, VmClass thisClass, VmClass moduleClass, Set<VmType> result) {
+    if (type == UnknownType.INSTANCE
+        || type == NothingType.INSTANCE
+        || type instanceof VmType.StringLiteralType) {
       result.add(type);
-    } else if (type instanceof PType.Class clazz) {
-      if (clazz.getTypeArguments().isEmpty()) {
-        // if a generic type is used without type arguments, it needs to be normalized so all args
-        // are unknown; i.e. with bare List/Map/etc. type annotations (via FinalClassTypeNode).
-        var typeParameterCount = clazz.getPClass().getTypeParameters().size();
-        result.add(
-            typeParameterCount == 0
-                ? clazz
-                : new PType.Class(
-                    clazz.getPClass(), Collections.nCopies(typeParameterCount, PType.UNKNOWN)));
+    } else if (type instanceof VmType.ClassType ct) {
+      if (!ct.isParametric()) {
+        result.add(ct);
       } else {
-        var typeArgs = new ArrayList<PType>(clazz.getTypeArguments().size());
-        for (var arg : clazz.getTypeArguments()) {
-          typeArgs.add(normalizeTypes(arg, thisClass, moduleClass));
-        }
-        result.add(new PType.Class(clazz.getPClass(), typeArgs));
+        result.add(
+            ct.withTypeArguments(
+                Arrays.stream(ct.getTypeArguments())
+                    .map(arg -> normalizeTypes(arg, thisClass, moduleClass))
+                    .toArray(VmType[]::new)));
       }
     }
     // normalize `T?` to `T | Null`
-    else if (type instanceof PType.Nullable nullable) {
-      normalizeTypes(nullable.getBaseType(), result, thisClass, moduleClass);
-      result.add(new PType.Class(BaseModule.getNullClass().export()));
+    else if (type instanceof VmType.NullableType nullable) {
+      normalizeTypes(nullable.getElementType(), thisClass, moduleClass, result);
+      result.add(new VmType.ClassType(BaseModule.getNullClass()));
       // erase `T(someConstraint)` to `T`
-    } else if (type instanceof PType.Constrained constrained) {
-      normalizeTypes(constrained.getBaseType(), result, thisClass, moduleClass);
-    } else if (type instanceof PType.Alias alias) {
-      if (isPreservedTypeAlias(alias.getTypeAlias())) {
+    } else if (type instanceof VmType.ConstrainedType constrained) {
+      normalizeTypes(constrained.getBaseType(), thisClass, moduleClass, result);
+    } else if (type instanceof VmType.AliasType alias) {
+      if (isPreservedTypeAlias(alias.getVmTypeAlias())) {
         result.add(alias);
       } else {
-        normalizeTypes(alias.getAliasedType(), result, thisClass, moduleClass);
+        normalizeTypes(
+            alias.getAliasedType(),
+            alias.getVmTypeAlias().getModuleClass(),
+            alias.getVmTypeAlias().getModuleClass(),
+            result);
       }
-    } else if (type instanceof PType.Union union) {
+    } else if (type instanceof VmType.UnionType union) {
       for (var t : union.getElementTypes()) {
-        normalizeTypes(t, result, thisClass, moduleClass);
+        normalizeTypes(t, thisClass, moduleClass, result);
       }
-    } else if (type == PType.THIS) {
-      assert thisClass != null;
+    } else if (type instanceof NonFinalThisType) {
       // there are 4 entrypoints here:
       // 1. init via the Reference constructor can only normalize an unparameterized PType.Class
       // 2. typecheck via ReferenceTypeNode erases self types to their actual PType.Class
@@ -161,13 +161,11 @@ public final class VmReference extends VmValue {
       // 4. property access uses the enclosing receiver's class to substitute for these self types
       // only property access and typecheck can produce THIS or MODULE.
       // getCandidatePropertyType and referentTypeIsSubtypeOf always pass non-null `thisClass`.
-      result.add(thisClass);
-    } else if (type == PType.MODULE) {
+      result.add(new VmType.ClassType(thisClass));
+    } else if (type instanceof NonFinalModuleType) {
       // this can be incorrect for usage of the module type in a class's property type annotation,
       // which is deprecated!!
-      assert moduleClass != null;
-      // see PType.THIS case above
-      result.add(moduleClass);
+      result.add(new VmType.ClassType(moduleClass));
     } else {
       // remaining types: PType.Function, PType.TypeVariable. no normalizing needed; TypeVariable
       // gets replaced upon instantiation, and Function can bubble up to users as a reference error
@@ -177,9 +175,9 @@ public final class VmReference extends VmValue {
     }
   }
 
-  private static Iterable<PType> iterateTypes(PType t) {
-    if (t instanceof PType.Union union) return union.getElementTypes();
-    return Collections.singleton(t);
+  private static VmType[] iterateTypes(VmType t) {
+    if (t instanceof VmType.UnionType union) return union.getElementTypes();
+    return new VmType[] {t};
   }
 
   public VmReference withPropertyAccess(Identifier property) {
@@ -197,8 +195,8 @@ public final class VmReference extends VmValue {
 
   @TruffleBoundary
   private VmReference withAccess(
-      BiConsumer<PType, Set<PType>> checkCandidate, Supplier<VmTyped> makeAccess) {
-    Set<PType> candidates = new HashSet<>();
+      BiConsumer<VmType, Set<VmType>> checkCandidate, Supplier<VmTyped> makeAccess) {
+    Set<VmType> candidates = new HashSet<>();
     for (var t : iterateTypes(referentType)) {
       checkCandidate.accept(t, candidates);
     }
@@ -206,51 +204,51 @@ public final class VmReference extends VmValue {
   }
 
   @SuppressWarnings("DuplicatedCode")
-  private static void getCandidatePropertyType(PType type, String property, Set<PType> result) {
-    if (type == PType.UNKNOWN) {
+  private static void getCandidatePropertyType(VmType type, String property, Set<VmType> result) {
+    if (type == UnknownType.INSTANCE) {
       result.add(type);
       return;
     }
     // restriction: only class types can have their properties referenced
-    if (!(type instanceof PType.Class clazz)) {
+    if (!(type instanceof VmType.AbstractClassType ct)) {
       throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.CANNOT_FIND_MEMBER);
     }
-    if (clazz.getPClass().getInfo() == PClassInfo.Dynamic) {
+    if (ct.getVmClass().isDynamicClass()) {
       if (property.equals("default")) {
         // restriction: cannot reference Dynamic.default
         throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.DEFAULT_MEMBER);
       }
-      result.add(PType.UNKNOWN);
+      result.add(UnknownType.INSTANCE);
       return;
     }
     // restriction: cannot reference Listing/Mapping.default
-    if (clazz.getPClass().getInfo() == PClassInfo.Listing
-        || clazz.getPClass().getInfo() == PClassInfo.Mapping) {
+    if (ct.getVmClass().isListingClass() || ct.getVmClass().isMappingClass()) {
       var errorType =
           property.equals("default")
               ? VmReferenceAccessErrorType.DEFAULT_MEMBER
               : VmReferenceAccessErrorType.CANNOT_FIND_MEMBER;
       throw new VmReferenceAccessError(type, errorType);
     }
-    var baseModule = BaseModule.getModuleClass().export();
+    var baseModule = BaseModule.getModuleClass();
     // restriction: cannot reference Module.output.
     //   generalized: properties originally defined in external classes; the only extant example.
     // This is implemented specifically because this is the only case where an external class
     //   containing a property can be subclassed.
     // And this can't check prop.getOwner().isExternal() because fully overriding the property with
     //   a new type annotation means the owner isn't Module.
-    if (clazz.getPClass().isSubclassOf(baseModule) && property.equals("output")) {
+    if (ct.getVmClass().isSubclassOf(baseModule) && property.equals("output")) {
       throw new VmReferenceAccessError(
-          new PType.Class(baseModule), VmReferenceAccessErrorType.EXTERNAL_CLASS);
+          new VmType.ClassType(baseModule), VmReferenceAccessErrorType.EXTERNAL_CLASS);
     }
 
     // dot access on `Reference<D, Null>` gives `Reference<D, Null>`
-    if (clazz.getPClass().getInfo() == PClassInfo.Null) {
-      result.add(clazz);
+    if (ct.getVmClass().isNullClass()) {
+      result.add(ct);
       return;
     }
 
-    var prop = clazz.getPClass().getAllProperties().get(property);
+    var prop = ct.getVmClass().getAllProperties().get(Identifier.get(property));
+    //noinspection ConstantValue
     if (prop == null) {
       throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.CANNOT_FIND_MEMBER);
     }
@@ -260,58 +258,57 @@ public final class VmReference extends VmValue {
       throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.EXTERNAL_MEMBER);
     }
 
-    normalizeTypes(
-        prop.getType(), result, clazz, new PType.Class(clazz.getPClass().getModuleClass()));
-  }
-
-  private static PClassInfo<?> getClassInfo(Object value) {
-    if (value instanceof VmValue vmValue) return vmValue.getVmClass().getPClassInfo();
-    if (value instanceof String) return PClassInfo.String;
-    if (value instanceof Boolean) return PClassInfo.Boolean;
-    if (value instanceof Long) return PClassInfo.Int;
-    if (value instanceof Double) return PClassInfo.Float;
-    throw new PklBugException("Not a Pkl value: " + value.getClass());
+    // this handles the object-prop-in-class case because VmClass.getAllProperties() omits
+    // properties without type annotations that are defined in a superclass. e.g.:
+    // ```
+    // open class A { prop: String }
+    // class B extends A { prop = "foo" }
+    // ```
+    // In this case `VmClass[B].getAllProperties().get(<prop>)` will be A's prop, not B's
+    var propTypeNode = prop.getTypeNode();
+    var propType =
+        propTypeNode == null ? VmType.UnknownType.INSTANCE : propTypeNode.getTypeNode().getType();
+    normalizeTypes(propType, ct.getVmClass(), ct.getVmClass().getModuleClass(), result);
   }
 
   @SuppressWarnings("DuplicatedCode")
-  private static void getCandidateSubscriptType(PType type, Object key, Set<PType> result) {
-    if (type == PType.UNKNOWN) {
+  private static void getCandidateSubscriptType(VmType type, Object key, Set<VmType> result) {
+    if (type == UnknownType.INSTANCE) {
       result.add(type);
       return;
     }
-    if (!(type instanceof PType.Class clazz)) {
+    if (!(type instanceof VmType.ClassType ct)) {
       throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.CANNOT_FIND_MEMBER);
     }
-    if (clazz.getPClass().getInfo() == PClassInfo.Dynamic) {
-      result.add(PType.UNKNOWN);
+    var clazz = ct.getVmClass();
+    if (clazz.isDynamicClass()) {
+      result.add(UnknownType.INSTANCE);
       return;
     }
-    if (clazz.getPClass().getInfo() == PClassInfo.Listing
-        || clazz.getPClass().getInfo() == PClassInfo.List) {
+    if (clazz.isListingClass() || clazz.isListClass()) {
       if (!(key instanceof Long)) {
         throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.CANNOT_FIND_MEMBER);
       }
-      normalizeTypes(clazz.getTypeArguments().get(0), result, null, null);
+      normalizeTypes(ct.getTypeArguments()[0], clazz, clazz.getModuleClass(), result);
       return;
     }
-    if (clazz.getPClass().getInfo() == PClassInfo.Mapping
-        || clazz.getPClass().getInfo() == PClassInfo.Map) {
-      var typeArgs = clazz.getTypeArguments();
-      var keyTypes = normalizeTypes(typeArgs.get(0));
+    if (clazz.isMappingClass() || clazz.isMapClass()) {
+      var typeArgs = ct.getTypeArguments();
+      var keyTypes = normalizeTypes(typeArgs[0], clazz, clazz.getModuleClass());
       for (var kt : iterateTypes(keyTypes)) {
-        if (kt == PType.UNKNOWN
-            || (kt instanceof PType.Class klazz && klazz.getPClass().getInfo() == getClassInfo(key))
-            || (kt instanceof PType.StringLiteral stringLiteral
+        if (kt == UnknownType.INSTANCE
+            || (kt instanceof VmType.ClassType klazz && klazz.getVmClass() == VmUtils.getClass(key))
+            || (kt instanceof VmType.StringLiteralType stringLiteral
                 && stringLiteral.getLiteral().equals(key))) {
-          normalizeTypes(typeArgs.get(1), result, null, null);
+          normalizeTypes(typeArgs[1], clazz, clazz.getModuleClass(), result);
           return;
         }
       }
     }
 
     // subscript access on `Reference<D, Null>` gives `Reference<D, Null>`
-    if (clazz.getPClass().getInfo() == PClassInfo.Null) {
-      result.add(clazz);
+    if (clazz == BaseModule.getNullClass()) {
+      result.add(ct);
       return;
     }
 
@@ -321,151 +318,52 @@ public final class VmReference extends VmValue {
   /**
    * Tells if this reference's referent type is a subtype of {@code type}. Does not check domain.
    */
-  @TruffleBoundary
-  public boolean referentTypeIsSubtypeOf(PType type, PClass thisClass, PClass moduleClass) {
+  public boolean referentTypeIsSubtypeOf(VmType type, VmClass thisClass, VmClass moduleClass) {
     // fast path: if referent is unknown it can match any type check
-    if (referentType == PType.UNKNOWN) {
+    if (referentType == UnknownType.INSTANCE) {
       return true;
     }
 
-    var checkType = normalizeTypes(type, new PType.Class(thisClass), new PType.Class(moduleClass));
+    var checkType = normalizeTypes(type, thisClass, moduleClass);
     // fast path: short circuit if any referent is accepted
-    if (checkType == PType.UNKNOWN || isClass(checkType, BaseModule.getAnyClass().export())) {
+    if (checkType == UnknownType.INSTANCE || isClass(checkType, BaseModule.getAnyClass())) {
       return true;
     }
     // fast path: short circuit if nothing is accepted
-    if (checkType == PType.NOTHING) {
+    if (checkType == NothingType.INSTANCE) {
       return false;
     }
 
-    return isSubtype(referentType, checkType);
+    return doReferentTypeIsSubtypeOf(checkType);
   }
 
-  private static boolean containsClass(Set<PType> types, PClass pClass) {
+  @TruffleBoundary
+  private boolean doReferentTypeIsSubtypeOf(VmType checkType) {
+    return referentType.isSubtypeOf(checkType);
+  }
+
+  private static boolean containsClass(Set<VmType> types, VmClass clazz) {
     for (var t : types) {
-      if (isClass(t, pClass)) return true;
+      if (isClass(t, clazz)) return true;
     }
     return false;
   }
 
-  private static boolean isClass(PType t, PClass pClass) {
-    return t instanceof PType.Class clazz && clazz.getPClass() == pClass;
+  private static boolean isClass(VmType t, VmClass clazz) {
+    return t instanceof VmType.ClassType ct && ct.getVmClass() == clazz;
   }
 
-  private static boolean isSubtype(PType a, PType b) {
-    // checks if A is a subtype of B
-    // cases (A -> B)
-    // * A == B
-    // * StringLiteral -> StringLiteral: if literals are the same
-    // * StringLiteral -> Class: B is String
-    // * Char Alias -> Char Alias, StringLiteral (known single character)
-    // * Int Alias -> Class: B is a subtype of Number (Int|Float|Number)
-    // * Int Alias -> Alias
-    //   * same alias
-    //   * Int8 is Int16|Int32
-    //   * Int16 is Int32
-    //   * UInt8 is Int16|Int32|Uint16|UInt32|UInt
-    //   * UInt16 is Int32|UInt32|UInt
-    //   * UInt32 is UInt
-    // * Class -> Class: if same class or A is a subclass of B
-    //   * if type args are present, must have equal number of them
-    //   * for each pair of type args, check variance
-    //     * invariant: A_i must be identical to B_i
-    //     * covariant: A_i must be a subtype of B_i
-    //     * contravariant: B_i must be a subtype of A_i
-    // * Union -> Union: Each elem of A must be a subtype of at least one elem of B
-    // * Non-union -> Union: A must be a subtype of at least one elem of B
-    if (a == b) return true;
-
-    if (a instanceof PType.StringLiteral aStr) {
-      if (b instanceof PType.StringLiteral bStr) {
-        return aStr.getLiteral().equals(bStr.getLiteral());
-      } else if (b instanceof PType.Class bClass) {
-        return bClass.getPClass() == BaseModule.getStringClass().export();
-      }
-    } else if (a instanceof PType.Alias aAlias) {
-      var aa = aAlias.getTypeAlias();
-      if (isIntTypeAlias(aa)) {
-        // special casing for stdlib Int typealiases
-        if (b instanceof PType.Class bClass) {
-          // A is an int alias, B is a Number (sub)class
-          return bClass.getPClass().isSubclassOf(BaseModule.getNumberClass().export());
-        } else if (b instanceof PType.Alias bAlias) {
-          var bb = bAlias.getTypeAlias();
-          if (aa == bb) {
-            return true;
-          }
-          if (aa == BaseModule.getInt8TypeAlias().export()) {
-            return bb == BaseModule.getInt16TypeAlias().export()
-                || bb == BaseModule.getInt32TypeAlias().export();
-          } else if (aa == BaseModule.getInt16TypeAlias().export()) {
-            return bb == BaseModule.getInt32TypeAlias().export();
-          } else if (aa == BaseModule.getUInt8TypeAlias().export()) {
-            return bb == BaseModule.getInt16TypeAlias().export()
-                || bb == BaseModule.getInt32TypeAlias().export()
-                || bb == BaseModule.getUInt16TypeAlias().export()
-                || bb == BaseModule.getUInt32TypeAlias().export()
-                || bb == BaseModule.getUIntTypeAlias().export();
-          } else if (aa == BaseModule.getUInt16TypeAlias().export()) {
-            return bb == BaseModule.getInt32TypeAlias().export()
-                || bb == BaseModule.getUInt32TypeAlias().export()
-                || bb == BaseModule.getUIntTypeAlias().export();
-          } else if (aa == BaseModule.getUInt32TypeAlias().export()) {
-            return bb == BaseModule.getUIntTypeAlias().export();
-          }
-        }
-      }
-    } else if (a instanceof PType.Class aClass && b instanceof PType.Class bClass) {
-      if (!aClass.getPClass().isSubclassOf(bClass.getPClass())) {
-        return false;
-      }
-      var aArgs = aClass.getTypeArguments();
-      var bArgs = bClass.getTypeArguments();
-      var bParams = bClass.getPClass().getTypeParameters();
-      if (aArgs.size() != bArgs.size()) {
-        return false;
-      }
-      // check variance of type args pairwise
-      for (var i = 0; i < aArgs.size(); i++) {
-        if (!switch (bParams.get(i).getVariance()) {
-          case INVARIANT -> aArgs.get(i) == bArgs.get(i);
-          case COVARIANT -> isSubtype(aArgs.get(i), bArgs.get(i));
-          case CONTRAVARIANT -> isSubtype(bArgs.get(i), aArgs.get(i));
-        }) {
-          return false;
-        }
-      }
-      return true;
-    } else if (b instanceof PType.Union bUnion) {
-      if (a instanceof PType.Union aUnion) {
-        a:
-        for (var aElem : aUnion.getElementTypes()) {
-          for (var bElem : bUnion.getElementTypes()) {
-            if (isSubtype(aElem, bElem)) continue a;
-          }
-          return false;
-        }
-        return true;
-      } else {
-        for (var bElem : bUnion.getElementTypes()) {
-          if (isSubtype(a, bElem)) return true;
-        }
-      }
-    }
-    return false;
+  private static boolean isIntTypeAlias(VmTypeAlias t) {
+    return t == BaseModule.getInt8TypeAlias()
+        || t == BaseModule.getInt16TypeAlias()
+        || t == BaseModule.getInt32TypeAlias()
+        || t == BaseModule.getUInt8TypeAlias()
+        || t == BaseModule.getUInt16TypeAlias()
+        || t == BaseModule.getUInt32TypeAlias()
+        || t == BaseModule.getUIntTypeAlias();
   }
 
-  private static boolean isIntTypeAlias(TypeAlias t) {
-    return t == BaseModule.getInt8TypeAlias().export()
-        || t == BaseModule.getInt16TypeAlias().export()
-        || t == BaseModule.getInt32TypeAlias().export()
-        || t == BaseModule.getUInt8TypeAlias().export()
-        || t == BaseModule.getUInt16TypeAlias().export()
-        || t == BaseModule.getUInt32TypeAlias().export()
-        || t == BaseModule.getUIntTypeAlias().export();
-  }
-
-  private static boolean isPreservedTypeAlias(TypeAlias t) {
+  private static boolean isPreservedTypeAlias(VmTypeAlias t) {
     return isIntTypeAlias(t);
   }
 
@@ -494,13 +392,14 @@ public final class VmReference extends VmValue {
       pathList.add(elem.export());
     }
 
-    return new Reference(domain.export(), VmValue.export(data), pathList, getReferentType());
+    return new Reference(
+        domain.export(), VmValue.export(data), pathList, getReferentType().export());
   }
 
-  public PType exportType() {
-    return new PType.Class(
-        RefModule.getReferenceClass().export(),
-        new PType.Class(domain.getVmClass().export()),
+  public VmType getType() {
+    return new VmType.ClassType(
+        RefModule.getReferenceClass(),
+        new VmType.ClassType(domain.getVmClass()),
         getReferentType());
   }
 
@@ -554,15 +453,15 @@ public final class VmReference extends VmValue {
   }
 
   public static final class VmReferenceAccessError extends RuntimeException {
-    private final PType type;
+    private final VmType type;
     private final VmReferenceAccessErrorType errorType;
 
-    public VmReferenceAccessError(PType type, VmReferenceAccessErrorType errorType) {
+    public VmReferenceAccessError(VmType type, VmReferenceAccessErrorType errorType) {
       this.type = type;
       this.errorType = errorType;
     }
 
-    public PType getType() {
+    public VmType getType() {
       return type;
     }
 

pkl-core/src/main/java/org/pkl/core/runtime/VmType.java

@@ -0,0 +1,767 @@
+/*
+ * Copyright © 2026 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.runtime;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Function;
+import org.jspecify.annotations.Nullable;
+import org.pkl.core.PType;
+import org.pkl.core.PType.Alias;
+import org.pkl.core.PType.Constrained;
+import org.pkl.core.PType.StringLiteral;
+import org.pkl.core.PType.TypeVariable;
+import org.pkl.core.PType.Union;
+import org.pkl.core.TypeParameter;
+import org.pkl.core.ValueFormatter;
+
+public abstract sealed class VmType {
+
+  public abstract PType export();
+
+  /** Checks if two types are equivalent. {@code other} will never be an {@link AliasType}. */
+  protected abstract boolean doIsEquivalentTo(VmType other);
+
+  /** Checks if this type is a supertype of {@code other}. */
+  protected abstract boolean doIsSupertypeOf(VmType other);
+
+  @SuppressWarnings("BooleanMethodIsAlwaysInverted")
+  public boolean isParametric() {
+    return false;
+  }
+
+  public @Nullable VmClass getVmClass() {
+    return null;
+  }
+
+  /** Tells if this type is the same typecheck as the other type. */
+  @Override
+  public final boolean equals(@Nullable Object value) {
+    if (this == value) return true;
+    if (!(value instanceof VmType other)) return false;
+    while (other instanceof AliasType at) {
+      other = at.aliasedType;
+    }
+    return doIsEquivalentTo(other);
+  }
+
+  public final boolean isSubtypeOf(VmType other) {
+    return other.isSupertypeOf(this);
+  }
+
+  public final boolean isSupertypeOf(VmType other) {
+    return equals(other)
+        || doIsSupertypeOf(other)
+        || other == UnknownType.INSTANCE // all types are supertypes/subtypes of unknown
+        || other == NothingType.INSTANCE
+        || other instanceof TypeVariableType
+        || (other instanceof UnionType ut && ut.allElementsMatch(this::isSupertypeOf))
+        || (other instanceof AliasType at && isSupertypeOf(at.aliasedType))
+        || (other instanceof ConstrainedType ct && isSupertypeOf(ct.baseType));
+  }
+
+  public static final class UnknownType extends VmType {
+    public static final UnknownType INSTANCE = new UnknownType();
+
+    private UnknownType() {}
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      // equality checked by equals()
+      return false;
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      // unknown is supertype of everything!
+      return true;
+    }
+
+    @Override
+    public PType export() {
+      return PType.UNKNOWN;
+    }
+
+    @Override
+    public String toString() {
+      return "unknown";
+    }
+  }
+
+  public static final class NothingType extends VmType {
+    public static final NothingType INSTANCE = new NothingType();
+
+    private NothingType() {}
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      // equality checked by equals()
+      return false;
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      // nothing is a supertype of nothing (except itself and unknown, handled by callers)
+      return false;
+    }
+
+    @Override
+    public PType export() {
+      return PType.NOTHING;
+    }
+
+    @Override
+    public String toString() {
+      return "nothing";
+    }
+  }
+
+  public static final class StringLiteralType extends VmType {
+    private final String literal;
+
+    public StringLiteralType(String literal) {
+      super();
+      this.literal = literal;
+    }
+
+    public String getLiteral() {
+      return literal;
+    }
+
+    @Override
+    public PType export() {
+      return new StringLiteral(literal);
+    }
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      return other instanceof StringLiteralType t && literal.equals(t.literal);
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      // equivalence handled by caller
+      return false;
+    }
+
+    @Override
+    public String toString() {
+      return ValueFormatter.basic().formatStringValue(literal, "");
+    }
+
+    @Override
+    public int hashCode() {
+      return 31 * literal.hashCode();
+    }
+  }
+
+  public abstract static sealed class AbstractClassType extends VmType {
+    protected final VmClass clazz;
+    protected final VmType[] typeArguments;
+
+    protected AbstractClassType(VmClass clazz, VmType[] typeArguments) {
+      this.clazz = clazz;
+      this.typeArguments = typeArguments;
+    }
+
+    public final VmType[] getTypeArguments() {
+      return typeArguments;
+    }
+
+    @Override
+    public final VmClass getVmClass() {
+      return clazz;
+    }
+
+    @Override
+    public final boolean isParametric() {
+      return typeArguments.length > 0;
+    }
+
+    public final boolean isFunctionNClass() {
+      return clazz.isFunctionNClass();
+    }
+
+    @Override
+    protected final boolean doIsEquivalentTo(VmType other) {
+      if (!(other instanceof AbstractClassType t)) return false;
+      if (clazz != t.clazz) return false;
+      return typesEquals(typeArguments, t.typeArguments);
+    }
+
+    @Override
+    protected final boolean doIsSupertypeOf(VmType other) {
+      // special case: Any is a supertype of everything
+      if (clazz == BaseModule.getAnyClass()) return true;
+      // special case: String is a supertype of all string literals and also Char
+      if (clazz == BaseModule.getStringClass()
+          && (other instanceof StringLiteralType
+              || (other instanceof AliasType at && at.typeAlias == BaseModule.getCharTypeAlias())))
+        return true;
+      // special case: Int is a supertype of range-constrained aliases
+      if ((clazz == BaseModule.getIntClass() || clazz == BaseModule.getNumberClass())
+          && other instanceof AliasType at
+          && (at.typeAlias == BaseModule.getInt8TypeAlias()
+              || at.typeAlias == BaseModule.getInt16TypeAlias()
+              || at.typeAlias == BaseModule.getInt32TypeAlias()
+              || at.typeAlias == BaseModule.getUIntTypeAlias()
+              || at.typeAlias == BaseModule.getUInt8TypeAlias()
+              || at.typeAlias == BaseModule.getUInt16TypeAlias()
+              || at.typeAlias == BaseModule.getUInt32TypeAlias())) return true;
+      // special case: class types are the supertype of non-final self types "rooted" to a subclass
+      if (other instanceof NonFinalSelfType st) {
+        return clazz.isSuperclassOf(st.clazz);
+      }
+
+      // standard case: other is a AbstractClassType
+      if (!(other instanceof AbstractClassType ct)) return false;
+      // if clazz isn't a superclass of other's we're not a supertype
+      if (!clazz.isSuperclassOf(ct.clazz)) return false;
+      // if our class has no type params, we are a supertype
+      if (clazz.getTypeParameterCount() == 0) return true;
+
+      // check generic type args: walk ct.clazz to clazz, substituting type arguments as we go
+      // handles arbitrary generics like Function2<A, B, R> -> Function<R>
+
+      var goalState =
+          typeArguments.length > 0
+              ? typeArguments
+              : nCopies(clazz.getTypeParameterCount(), ClassType.ANY);
+      var state =
+          ct.typeArguments.length > 0
+              ? ct.typeArguments
+              : nCopies(ct.clazz.getTypeParameterCount(), ClassType.ANY);
+      for (var c = ct.clazz; c != clazz; c = c.getSuperclass()) {
+        assert c != null; // we know walking parents reaches clazz before null
+        var cSuperclass = c.getSuperclass();
+        assert cSuperclass != null; // we know c has a superclass
+        var cSupertype = (AbstractClassType) c.getSupertype();
+        assert cSupertype != null; // we know c has a supertype
+
+        if (cSupertype.typeArguments.length == 0) {
+          // supertype args could be omitted, e.g. class MyList<T> extends List
+          state = nCopies(cSuperclass.getTypeParameterCount(), ClassType.ANY);
+          continue;
+        } else if (state.length == 0) {
+          // subclass may not have type args, e.g. class A extends B<Int>
+          state = cSupertype.typeArguments;
+          continue;
+        }
+
+        // otherwise, clone supertype args and substitute any type vars
+        var newState = cSupertype.typeArguments.clone();
+        for (var i = 0; i < newState.length; i++) {
+          if (!(newState[i] instanceof TypeVariableType tvt)) continue;
+          newState[i] = state[tvt.typeParameter.getIndex()];
+        }
+        state = newState;
+      }
+
+      // do variance checking
+      assert goalState.length == state.length;
+      var params = clazz.getTypeParameters();
+      for (var i = 0; i < goalState.length; i++) {
+        if (!switch (params.get(i).getVariance()) {
+          case INVARIANT -> state[i].equals(goalState[i]);
+          case COVARIANT -> state[i].isSubtypeOf(goalState[i]);
+          case CONTRAVARIANT -> state[i].isSupertypeOf(goalState[i]);
+        }) return false;
+      }
+      return true;
+    }
+
+    @Override
+    public final int hashCode() {
+      return 31 * clazz.hashCode() + Arrays.hashCode(typeArguments);
+    }
+  }
+
+  public static final class ClassType extends AbstractClassType {
+    public ClassType(VmClass clazz) {
+      super(clazz, new VmType[0]);
+    }
+
+    public ClassType(VmClass clazz, VmType typeArgument) {
+      super(clazz, new VmType[] {typeArgument});
+    }
+
+    public ClassType(VmClass clazz, VmType typeArgument1, VmType typeArgument2) {
+      super(clazz, new VmType[] {typeArgument1, typeArgument2});
+    }
+
+    public ClassType(VmClass clazz, VmType[] typeArguments) {
+      super(clazz, typeArguments);
+    }
+
+    private static final ClassType ANY = new ClassType(BaseModule.getAnyClass());
+
+    public VmType.ClassType withTypeArguments(VmType[] typeArguments) {
+      return new VmType.ClassType(clazz, typeArguments);
+    }
+
+    @Override
+    public PType export() {
+      return typeArguments.length > 0 && clazz.isFunctionNClass()
+          ? new PType.Function(
+              exportTypes(typeArguments, 1), typeArguments[typeArguments.length - 1].export())
+          : new PType.Class(clazz.export(), exportTypes(typeArguments));
+    }
+
+    @Override
+    public String toString() {
+      if (typeArguments.length > 0 && clazz.isFunctionNClass()) {
+        var paramCount = typeArguments.length - 1;
+        var sb = new StringBuilder("(");
+        for (var i = 0; i < paramCount; i++) {
+          sb.append(typeArguments[i]);
+          if (i < paramCount - 1) {
+            sb.append(", ");
+          }
+        }
+        sb.append(") -> ");
+        sb.append(typeArguments[typeArguments.length - 1]);
+        return sb.toString();
+      }
+
+      if (typeArguments.length == 0) return clazz.getDisplayName();
+      return appendTypeArguments(new StringBuilder(clazz.getDisplayName()), typeArguments)
+          .toString();
+    }
+  }
+
+  public static final class FinalModuleType extends AbstractClassType {
+    public FinalModuleType(VmClass clazz) {
+      super(clazz, new VmType[0]);
+    }
+
+    @Override
+    public PType export() {
+      return PType.MODULE;
+    }
+
+    @Override
+    public String toString() {
+      return "module";
+    }
+  }
+
+  public static final class FinalThisType extends AbstractClassType {
+    public FinalThisType(VmClass clazz) {
+      super(clazz, new VmType[0]);
+    }
+
+    @Override
+    public PType export() {
+      return PType.THIS;
+    }
+
+    @Override
+    public String toString() {
+      return "this";
+    }
+  }
+
+  private abstract static sealed class NonFinalSelfType extends VmType {
+    private final VmClass clazz;
+
+    protected NonFinalSelfType(VmClass clazz) {
+      this.clazz = clazz;
+    }
+
+    @Override
+    public final VmClass getVmClass() {
+      return clazz;
+    }
+
+    @Override
+    protected final boolean doIsEquivalentTo(VmType other) {
+      return other instanceof NonFinalSelfType st && clazz == st.clazz;
+    }
+
+    @Override
+    protected final boolean doIsSupertypeOf(VmType other) {
+      return other instanceof NonFinalSelfType st && clazz.isSuperclassOf(st.clazz);
+    }
+
+    @Override
+    public final int hashCode() {
+      return 31 * clazz.hashCode();
+    }
+  }
+
+  public static final class NonFinalModuleType extends NonFinalSelfType {
+    public NonFinalModuleType(VmClass clazz) {
+      super(clazz);
+    }
+
+    @Override
+    public PType export() {
+      return PType.MODULE;
+    }
+
+    @Override
+    public String toString() {
+      return "module";
+    }
+  }
+
+  public static final class NonFinalThisType extends NonFinalSelfType {
+    public NonFinalThisType(VmClass clazz) {
+      super(clazz);
+    }
+
+    @Override
+    public PType export() {
+      return PType.THIS;
+    }
+
+    @Override
+    public String toString() {
+      return "this";
+    }
+  }
+
+  public static final class NullableType extends VmType {
+    private final VmType elementType;
+
+    public NullableType(VmType elementType) {
+      this.elementType = elementType;
+    }
+
+    public VmType getElementType() {
+      return elementType;
+    }
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      return other instanceof NullableType t && elementType.equals(t.elementType);
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      if (other instanceof NullableType nt) return elementType.isSupertypeOf(nt.elementType);
+      return elementType.isSupertypeOf(other);
+    }
+
+    @Override
+    public PType export() {
+      return new PType.Nullable(elementType.export());
+    }
+
+    @Override
+    public String toString() {
+      return (elementType instanceof ClassType ct && ct.isFunctionNClass())
+              || elementType instanceof UnionType
+          ? "(" + elementType + ")?"
+          : elementType + "?";
+    }
+
+    @Override
+    public int hashCode() {
+      return 31 * elementType.hashCode();
+    }
+  }
+
+  public static final class ConstrainedType extends VmType {
+    private final VmType baseType;
+    private final String[] constraints;
+    private final int identity;
+
+    public ConstrainedType(VmType baseType, String[] constraints, int identity) {
+      this.baseType = baseType;
+      this.constraints = constraints;
+      this.identity = identity;
+    }
+
+    public VmType getBaseType() {
+      return baseType;
+    }
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      // consider constrained equivalent only on identity
+      return other instanceof ConstrainedType t && t.identity == identity;
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      // constrained types can never be supertypes (except when equal by identity, handled above)
+      return false;
+    }
+
+    @Override
+    public PType export() {
+      return new Constrained(baseType.export(), Arrays.asList(constraints));
+    }
+
+    @Override
+    public String toString() {
+      return ((baseType instanceof ClassType ct && ct.isFunctionNClass())
+                  || baseType instanceof UnionType
+              ? "(" + baseType + ")"
+              : baseType)
+          + "("
+          + String.join(", ", constraints)
+          + ")";
+    }
+
+    @Override
+    public int hashCode() {
+      return 31 * identity;
+    }
+  }
+
+  public static final class AliasType extends VmType {
+    private final VmTypeAlias typeAlias;
+    private final @Nullable VmClass clazz;
+    private final VmType[] typeArguments;
+    private final VmType aliasedType;
+
+    /** For intrinsified typealiases with an undetermined class (e.g. NonNull) */
+    public AliasType(VmTypeAlias typeAlias) {
+      this.typeAlias = typeAlias;
+      this.aliasedType = typeAlias.getTypeNode().getType();
+      this.typeArguments = new VmType[0];
+      this.clazz = aliasedType.getVmClass();
+    }
+
+    /** For intrinsified typealiases with an inherent class (e.g. Int aliases) */
+    public AliasType(VmTypeAlias typeAlias, VmClass clazz) {
+      this.typeAlias = typeAlias;
+      this.aliasedType = typeAlias.getTypeNode().getType();
+      this.typeArguments = new VmType[0];
+      this.clazz = clazz;
+    }
+
+    /** For arbitrary typealiases */
+    public AliasType(VmTypeAlias typeAlias, VmType[] typeArguments, VmType aliasedType) {
+      this.typeAlias = typeAlias;
+      this.typeArguments = typeArguments;
+      this.clazz = aliasedType.getVmClass();
+      this.aliasedType = aliasedType;
+    }
+
+    public VmTypeAlias getVmTypeAlias() {
+      return typeAlias;
+    }
+
+    public VmType getAliasedType() {
+      return aliasedType;
+    }
+
+    @Override
+    public @Nullable VmClass getVmClass() {
+      return clazz;
+    }
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      return aliasedType.equals(other);
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      if (other instanceof AliasType at) {
+        if (at.typeAlias == BaseModule.getInt8TypeAlias()
+            && (typeAlias == BaseModule.getInt16TypeAlias()
+                || typeAlias == BaseModule.getInt32TypeAlias())) return true;
+        if (at.typeAlias == BaseModule.getInt16TypeAlias()
+            && typeAlias == BaseModule.getInt32TypeAlias()) return true;
+        if (at.typeAlias == BaseModule.getUInt8TypeAlias()
+            && (typeAlias == BaseModule.getInt16TypeAlias()
+                || typeAlias == BaseModule.getInt32TypeAlias()
+                || typeAlias == BaseModule.getUInt16TypeAlias()
+                || typeAlias == BaseModule.getUInt32TypeAlias()
+                || typeAlias == BaseModule.getUIntTypeAlias())) return true;
+        if (at.typeAlias == BaseModule.getUInt16TypeAlias()
+            && (typeAlias == BaseModule.getInt32TypeAlias()
+                || typeAlias == BaseModule.getUInt32TypeAlias()
+                || typeAlias == BaseModule.getUIntTypeAlias())) return true;
+        if (at.typeAlias == BaseModule.getUInt32TypeAlias()
+            && typeAlias == BaseModule.getUIntTypeAlias()) return true;
+      }
+
+      return aliasedType.isSupertypeOf(other);
+    }
+
+    @Override
+    public PType export() {
+      return new Alias(typeAlias.export(), exportTypes(typeArguments), aliasedType.export());
+    }
+
+    @Override
+    public boolean isParametric() {
+      return typeArguments.length > 0;
+    }
+
+    @Override
+    public String toString() {
+      if (typeArguments.length == 0) return typeAlias.getDisplayName();
+      return appendTypeArguments(new StringBuilder(typeAlias.getDisplayName()), typeArguments)
+          .toString();
+    }
+
+    @Override
+    public int hashCode() {
+      return aliasedType.hashCode();
+    }
+  }
+
+  public static final class UnionType extends VmType {
+    private final int defaultIndex;
+    private final VmType[] elementTypes;
+
+    public UnionType(int defaultIndex, VmType[] elementTypes) {
+      this.defaultIndex = defaultIndex;
+      this.elementTypes = elementTypes;
+    }
+
+    public UnionType(int defaultIndex, String[] stringLiterals) {
+      this.defaultIndex = defaultIndex;
+      elementTypes = new VmType[stringLiterals.length];
+      for (var i = 0; i < elementTypes.length; i++) {
+        elementTypes[i] = new StringLiteralType(stringLiterals[i]);
+      }
+    }
+
+    public int getDefaultIndex() {
+      return defaultIndex;
+    }
+
+    public VmType[] getElementTypes() {
+      return elementTypes;
+    }
+
+    @Override
+    public PType export() {
+      return new Union(exportTypes(elementTypes));
+    }
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      if (!(other instanceof UnionType t)) return false;
+      // TODO: handle A | B as equivalent to B | A
+      return typesEquals(elementTypes, t.elementTypes);
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      for (var member : elementTypes) {
+        if (member.isSupertypeOf(other)) return true;
+      }
+      return false;
+    }
+
+    public boolean isUnionOfStringLiterals() {
+      return allElementsMatch(it -> it instanceof StringLiteralType);
+    }
+
+    @Override
+    public String toString() {
+      var sb = new StringBuilder();
+      for (var i = 0; i < elementTypes.length; i++) {
+        sb.append(elementTypes[i]);
+        if (i < elementTypes.length - 1) {
+          sb.append(" | ");
+        }
+      }
+      return sb.toString();
+    }
+
+    @Override
+    public int hashCode() {
+      return Arrays.hashCode(elementTypes);
+    }
+
+    boolean allElementsMatch(Function<VmType, Boolean> predicate) {
+      for (var member : elementTypes) {
+        if (!predicate.apply(member)) return false;
+      }
+      return true;
+    }
+  }
+
+  public static final class TypeVariableType extends VmType {
+    private final TypeParameter typeParameter;
+
+    public TypeVariableType(TypeParameter typeParameter) {
+      this.typeParameter = typeParameter;
+    }
+
+    public TypeParameter getTypeParameter() {
+      return typeParameter;
+    }
+
+    @Override
+    protected boolean doIsEquivalentTo(VmType other) {
+      return other instanceof TypeVariableType;
+    }
+
+    @Override
+    protected boolean doIsSupertypeOf(VmType other) {
+      return true;
+    }
+
+    @Override
+    public PType export() {
+      return new TypeVariable(typeParameter);
+    }
+
+    @Override
+    public String toString() {
+      return typeParameter.getName();
+    }
+
+    @Override
+    public int hashCode() {
+      return -318019;
+    }
+  }
+
+  private static boolean typesEquals(VmType[] a, VmType[] b) {
+    if (a.length != b.length) return false;
+    for (var i = 0; i < a.length; i++) {
+      if (!a[i].equals(b[i])) return false;
+    }
+    return true;
+  }
+
+  private static List<PType> exportTypes(VmType[] types) {
+    return Arrays.stream(types).map(VmType::export).toList();
+  }
+
+  private static List<PType> exportTypes(VmType[] types, int drop) {
+    return Arrays.stream(types).limit(types.length - drop).map(VmType::export).toList();
+  }
+
+  private static VmType[] nCopies(int len, VmType type) {
+    var ret = new VmType[len];
+    Arrays.fill(ret, type);
+    return ret;
+  }
+
+  private static StringBuilder appendTypeArguments(StringBuilder sb, VmType[] typeArguments) {
+    sb.append('<');
+    for (var i = 0; i < typeArguments.length; i++) {
+      sb.append(typeArguments[i]);
+      if (i < typeArguments.length - 1) {
+        sb.append(", ");
+      }
+    }
+    sb.append('>');
+    return sb;
+  }
+}

pkl-core/src/main/java/org/pkl/core/runtime/VmTypeAlias.java

@@ -137,6 +137,10 @@ public final class VmTypeAlias extends VmValue {
     return annotations;
   }
 
+  public VmClass getModuleClass() {
+    return module.getVmClass();
+  }
+
   public String getModuleName() {
     return module.getVmClass().getModuleName();
   }

pkl-core/src/main/java/org/pkl/core/runtime/VmTypes.java

@@ -22,6 +22,7 @@ import com.oracle.truffle.api.dsl.TypeSystem;
   long.class,
   double.class,
   boolean.class,
+  VmType.class,
   VmDuration.class,
   VmDataSize.class,
   VmIntSeq.class,

pkl-core/src/main/java/org/pkl/core/stdlib/protobuf/RendererNodes.java

@@ -62,6 +62,7 @@ import org.pkl.core.runtime.VmPair;
 import org.pkl.core.runtime.VmReference;
 import org.pkl.core.runtime.VmRegex;
 import org.pkl.core.runtime.VmSet;
+import org.pkl.core.runtime.VmType;
 import org.pkl.core.runtime.VmTyped;
 import org.pkl.core.runtime.VmUtils;
 import org.pkl.core.runtime.VmValue;
@@ -118,7 +119,9 @@ public final class RendererNodes {
     var clazz =
         value instanceof VmValue vmValue
             ? vmValue.getVmClass()
-            : value instanceof TypeNode typeNode ? typeNode.getVmClass() : value.getClass();
+            : value instanceof TypeNode typeNode
+                ? typeNode.getType().getVmClass()
+                : value.getClass();
     if (clazz == null) {
       throw new VmExceptionBuilder()
           .evalError("cannotResolveTypeForProtobuf")
@@ -345,7 +348,7 @@ public final class RendererNodes {
               return computedName;
             }
           } else if (type instanceof NonFinalClassTypeNode) {
-            var clazz = type.getVmClass();
+            var clazz = type.getType().getVmClass();
             if (value instanceof VmValue vmValue) {
               if (clazz == vmValue.getVmClass()) {
                 return clazz.getSimpleName();
@@ -402,9 +405,9 @@ public final class RendererNodes {
             hasCollection = true;
             collectionType = setType.getElementTypeNode();
           } else if (type instanceof NonFinalClassTypeNode) {
-            if (type.getVmClass() != clazz) {
+            if (type.getType().getVmClass() != clazz) {
               throw new VmExceptionBuilder()
-                  .evalError("cannotRenderSubtypeForProtobuf", type.getVmClass(), clazz)
+                  .evalError("cannotRenderSubtypeForProtobuf", type.getType().getVmClass(), clazz)
                   .build();
             }
           }
@@ -581,7 +584,8 @@ public final class RendererNodes {
       } else if (type instanceof NullableTypeNode nullableType) {
         return resolveType(nullableType.getElementTypeNode());
       } else if (type instanceof TypeAliasTypeNode typeAliasType) {
-        return resolveType(typeAliasType.getVmTypeAlias().getTypeNode());
+        return resolveType(
+            ((VmType.AliasType) typeAliasType.getType()).getVmTypeAlias().getTypeNode());
       } else if (type instanceof ListingTypeNode listingType) {
         var valueType = resolveType(listingType.getValueTypeNode());
         assert valueType != null : "Failed to resolve type node.";
@@ -633,8 +637,8 @@ public final class RendererNodes {
         elements.sort(
             (o1, o2) -> {
               if (o1 instanceof ObjectSlotTypeNode && o2 instanceof ObjectSlotTypeNode) {
-                var t1 = o1.getVmClass();
-                var t2 = o2.getVmClass();
+                var t1 = o1.getType().getVmClass();
+                var t2 = o2.getType().getVmClass();
                 if (t1 == null || t2 == null) return 0;
                 return t1.isSubclassOf(t2) ? -1 : t2.isSubclassOf(t1) ? 1 : 0;
               }

pkl-core/src/main/resources/org/pkl/core/errorMessages.properties

@@ -359,7 +359,7 @@ typeMismatchBecause=\
 * Value is not of type `{0}` because:
 
 classTypeMismatchHint=\
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 typeConstraintViolated=\
 Type constraint `{0}` violated.

pkl-core/src/test/files/LanguageSnippetTests/input/api/reference.pkl

@@ -134,6 +134,9 @@ class BadResource extends Resource {
 
 badThisRef = test.catch(() -> new BadResource { name = "bad" }.$.toString())
 
+// test that a bare function type toStrings/exports okay
+bareFunctionType = test.catch(() -> ref.Reference(d, Function4, null) as Ref<String>)
+
 output {
   renderer {
     converters {

pkl-core/src/test/files/LanguageSnippetTests/output/api/reference.pcf

@@ -61,3 +61,4 @@ aValuesJoined = """
   """
 typeArgs = "${null.prop}"
 badThisRef = "Expected value of type `pkl.ref#Reference<reference#D, this>`, but got type `pkl.ref#Reference<reference#D, reference#A>`. Value: Reference(new D {}, reference#A, new BadResource { name = ? })"
+bareFunctionType = "Expected value of type `pkl.ref#Reference<reference#D, String>`, but got type `pkl.ref#Reference<reference#D, Function4>`. Value: Reference(new D {}, Function4, null)"

pkl-core/src/test/files/LanguageSnippetTests/output/errors/reference13.err

@@ -1,5 +1,5 @@
 –– Pkl Error ––
-Cannot find property `default` in object of type `pkl.ref#Reference<reference13#D, Mapping<unknown, unknown>>`.
+Cannot find property `default` in object of type `pkl.ref#Reference<reference13#D, Mapping>`.
 
 x | test = ref.Reference(d, Mapping, "").default
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/errors/reference14.err

@@ -1,5 +1,5 @@
 –– Pkl Error ––
-Cannot find property `default` in object of type `pkl.ref#Reference<reference14#D, Listing<unknown>>`.
+Cannot find property `default` in object of type `pkl.ref#Reference<reference14#D, Listing>`.
 
 x | test = ref.Reference(d, Listing, "").default
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/errors/reference26.err

@@ -1,11 +1,11 @@
 –– Pkl Error ––
-Cannot find property `name` in object of type `pkl.ref#Reference<reference26#D, Listing<unknown>>`.
+Cannot find property `name` in object of type `pkl.ref#Reference<reference26#D, Listing>`.
 
 x | res = myRef.name
           ^^^^^^^^^^
 at reference26#res (file:///$snippetsDir/input/errors/reference26.pkl)
 
-Cannot find property `name` in type `Listing<unknown>`.
+Cannot find property `name` in type `Listing`.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/errors/reference7.err

@@ -1,13 +1,13 @@
 –– Pkl Error ––
-Operator `[]` is not defined for operand types `pkl.ref#Reference<reference7#D, List<unknown>>` and `String`.
-Left operand : Reference(new D {}, List<unknown>, List())
+Operator `[]` is not defined for operand types `pkl.ref#Reference<reference7#D, List>` and `String`.
+Left operand : Reference(new D {}, List, List())
 Right operand: "hi"
 
 x | test = ref.Reference(d, List, List())["hi"]
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 at reference7#test (file:///$snippetsDir/input/errors/reference7.pkl)
 
-Operator `[]` is not defined for operand types `List<unknown>` and `String`.
+Operator `[]` is not defined for operand types `List` and `String`.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr11.err

@@ -5,7 +5,7 @@ xx | typealias F<T> = List<Class<T>>
                            ^^^^^^^^
 at classTypeErr11#res22 (file:///$snippetsDir/input/types/classType.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr12.err

@@ -5,7 +5,7 @@ xx | typealias F<T> = List<Class<T>>
                            ^^^^^^^^
 at classTypeErr12#res22 (file:///$snippetsDir/input/types/classType.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr13.err

@@ -5,7 +5,7 @@ xx | typealias F<T> = List<Class<T>>
                            ^^^^^^^^
 at classTypeErr13#res22 (file:///$snippetsDir/input/types/classType.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr4.err

@@ -5,7 +5,7 @@ x | res8 = C as Class<A | B>
                 ^^^^^^^^^^^^
 at classTypeErr4#res8 (file:///$snippetsDir/input/types/classTypeErr4.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr5.err

@@ -5,7 +5,7 @@ x | res9 = C as Class<A?>
                 ^^^^^^^^^
 at classTypeErr5#res9 (file:///$snippetsDir/input/types/classTypeErr5.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr6.err

@@ -5,7 +5,7 @@ x | res10 = C as Class<"foo">
                  ^^^^^^^^^^^^
 at classTypeErr6#res10 (file:///$snippetsDir/input/types/classTypeErr6.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr7.err

@@ -5,7 +5,7 @@ x | res11 = C as Class<nothing>
                  ^^^^^^^^^^^^^^
 at classTypeErr7#res11 (file:///$snippetsDir/input/types/classTypeErr7.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/files/LanguageSnippetTests/output/types/classTypeErr8.err

@@ -5,7 +5,7 @@ x | res12 = C as Class<A(true)>
                  ^^^^^^^^^^^^^^
 at classTypeErr8#res12 (file:///$snippetsDir/input/types/classTypeErr8.pkl)
 
-A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, or an alias to one of those types.
+A `Class` type check can only succeed when its type argument is an un-parameterized class, `unknown`, `module`, `this`, or an alias to one of those types.
 
 xxx | renderer.renderDocument(value)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pkl-core/src/test/kotlin/org/pkl/core/runtime/CommandSpecParserTest.kt

@@ -651,7 +651,8 @@ class CommandSpecParserTest {
 
     val exc = assertThrows<PklException> { parse(moduleUri) }
     assertThat(exc.message).contains("foo: Foo")
-    assertThat(exc.message).contains("Command option property `foo` has unsupported type `Foo`.")
+    assertThat(exc.message)
+      .contains("Command option property `foo` has unsupported type `cmd#Foo`.")
   }
 
   @Test
@@ -805,7 +806,7 @@ class CommandSpecParserTest {
     val spec = parse(moduleUri)
     val flag = spec.options.first() as CommandSpec.Flag
 
-    assertThat(flag.metavar()).isEqualTo("[json, toml, yaml]")
+    assertThat(flag.metavar()).isEqualTo("[json, yaml, toml]")
 
     val apply =
       assertThrows<CommandSpec.Option.BadValue> {

pkl-core/src/test/kotlin/org/pkl/core/runtime/VmTypeTest.kt

@@ -0,0 +1,450 @@
+/*
+ * Copyright © 2026 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.runtime
+
+import java.net.URI
+import java.nio.file.Path
+import kotlin.io.path.writeText
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Disabled
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.io.TempDir
+import org.pkl.core.Loggers
+import org.pkl.core.SecurityManagers
+import org.pkl.core.StackFrameTransformers
+import org.pkl.core.TypeParameter
+import org.pkl.core.evaluatorSettings.TraceMode
+import org.pkl.core.http.HttpClient
+import org.pkl.core.module.ModuleKey
+import org.pkl.core.module.ModuleKeyFactories
+import org.pkl.core.module.ModuleKeys.file
+import org.pkl.core.module.ModuleKeys.synthetic
+
+class VmTypeTest {
+
+  companion object {
+    val stringClass = VmType.ClassType(BaseModule.getStringClass())
+    val boolClass = VmType.ClassType(BaseModule.getBooleanClass())
+    val intClass = VmType.ClassType(BaseModule.getIntClass())
+    val numberClass = VmType.ClassType(BaseModule.getNumberClass())
+  }
+
+  private fun makeModule(rootDir: Path?, moduleKey: ModuleKey): VmTyped {
+    val securityManager =
+      SecurityManagers.standard(
+        SecurityManagers.defaultAllowedModules,
+        SecurityManagers.defaultAllowedResources,
+        SecurityManagers.defaultTrustLevels,
+        rootDir,
+      )
+    var ret: VmTyped? = null
+    VmUtils.createContext {
+        val vmContext = VmContext.get(null)
+        vmContext.initialize(
+          VmContext.Holder(
+            StackFrameTransformers.defaultTransformer,
+            securityManager,
+            HttpClient.dummyClient(),
+            ModuleResolver(
+              listOfNotNull(
+                ModuleKeyFactories.standardLibrary,
+                rootDir?.let { ModuleKeyFactories.file },
+              )
+            ),
+            ResourceManager(securityManager, listOf()),
+            Loggers.noop(),
+            mapOf(),
+            mapOf(),
+            null,
+            null,
+            null,
+            null,
+            TraceMode.COMPACT,
+            false,
+          )
+        )
+        ret = VmLanguage.get(null).loadModule(moduleKey)
+      }
+      .close()
+    return ret!!
+  }
+
+  private fun makeModule(text: String): VmTyped =
+    makeModule(null, synthetic(URI("repl:text"), text))
+
+  private fun makeModule(dir: Path, path: Path): VmTyped = makeModule(dir, file(path.toUri()))
+
+  private fun VmTyped.getTypeForProperty(property: String): VmType =
+    vmClass.getProperty(Identifier.get(property))!!.typeNode!!.typeNode.type
+
+  private fun VmTyped.getTypeForNestedProperty(prop1: String, prop2: String): VmType =
+    vmClass
+      .getProperty(Identifier.get(prop1))!!
+      .typeNode!!
+      .typeNode
+      .type
+      .vmClass!!
+      .getProperty(Identifier.get(prop2))!!
+      .typeNode!!
+      .typeNode
+      .type
+
+  /** Assert this is a subtype of [other] and [other] is a supertype of this, but not equivalent */
+  private fun VmType.sub(other: VmType) {
+    assertThat(this.isSubtypeOf(other)).`as`("%s isSubtypeOf %s", this, other).isTrue
+    assertThat(other.isSupertypeOf(this)).`as`("%s isSupertypeOf %s", other, this).isTrue
+    assertThat(other.isSubtypeOf(this)).`as`("%s isSubtypeOf %s", other, this).isFalse
+    assertThat(this.isSupertypeOf(other)).`as`("%s isSupertypeOf %s", this, other).isFalse
+    assertThat(this == other).`as`("%s == %s", this, other).isFalse
+    assertThat(other == this).`as`("%s == %s", other, this).isFalse
+  }
+
+  /**
+   * Assert this is a subtype of [other] and [other] is a supertype of this and they are equivalent
+   */
+  private fun VmType.eq(other: VmType) {
+    assertThat(this.isSubtypeOf(other)).`as`("%s isSubtypeOf %s", this, other).isTrue
+    assertThat(other.isSupertypeOf(this)).`as`("%s isSupertypeOf %s", other, this).isTrue
+    assertThat(other.isSubtypeOf(this)).`as`("%s isSubtypeOf %s", other, this).isTrue
+    assertThat(this.isSupertypeOf(other)).`as`("%s isSupertypeOf %s", this, other).isTrue
+    assertThat(this == other).`as`("%s == %s", this, other).isTrue
+    assertThat(other == this).`as`("%s == %s", other, this).isTrue
+  }
+
+  /** Assert this is a subtype of [other] and [other] is a subtype of this, but not equivalent */
+  private fun VmType.bidi(other: VmType) {
+    assertThat(this.isSubtypeOf(other)).`as`("%s isSubtypeOf %s", this, other).isTrue
+    assertThat(other.isSupertypeOf(this)).`as`("%s isSupertypeOf %s", other, this).isTrue
+    assertThat(other.isSubtypeOf(this)).`as`("%s isSubtypeOf %s", other, this).isTrue
+    assertThat(this.isSupertypeOf(other)).`as`("%s isSupertypeOf %s", this, other).isTrue
+    assertThat(this == other).`as`("%s == %s", this, other).isFalse
+    assertThat(other == this).`as`("%s == %s", other, this).isFalse
+  }
+
+  @Test
+  fun `unknown - equality (referential)`() {
+    VmType.UnknownType.INSTANCE.eq(VmType.UnknownType.INSTANCE)
+  }
+
+  @Test
+  fun `unknown - subtype and supertype of everything`() {
+    VmType.UnknownType.INSTANCE.bidi(VmType.ClassType(BaseModule.getStringClass()))
+  }
+
+  @Test
+  fun `nothing - equality (referential)`() {
+    VmType.NothingType.INSTANCE.eq(VmType.NothingType.INSTANCE)
+  }
+
+  @Test
+  fun `nothing - subtype of everything`() {
+    VmType.NothingType.INSTANCE.sub(VmType.ClassType(BaseModule.getStringClass()))
+    VmType.NothingType.INSTANCE.sub(VmType.StringLiteralType("foo"))
+  }
+
+  @Test
+  fun `final self - equality`(@TempDir tempDir: Path) {
+    val modPath = tempDir.resolve("test.pkl")
+    modPath.writeText(
+      """
+      module mod
+      import "test.pkl" as Declared
+
+      hidden moduleType: module
+      hidden moduleType2: module
+      hidden thisType: this
+      hidden thisType2: this
+      hidden declaredType: Declared
+      """
+        .trimIndent()
+    )
+    val mod = makeModule(tempDir, modPath)
+
+    assertThat(mod.vmClass.isOpen).isFalse
+    mod.getTypeForProperty("moduleType").eq(mod.getTypeForProperty("moduleType2"))
+    mod.getTypeForProperty("moduleType").eq(mod.getTypeForProperty("thisType"))
+    mod.getTypeForProperty("moduleType").eq(mod.getTypeForProperty("declaredType"))
+    mod.getTypeForProperty("thisType").eq(mod.getTypeForProperty("thisType2"))
+    mod.getTypeForProperty("thisType").eq(mod.getTypeForProperty("declaredType"))
+  }
+
+  @Test
+  fun `non-final self - equality`() {
+    val mod =
+      makeModule(
+        """
+        open module mod
+
+        hidden moduleType: module
+        hidden moduleType2: module
+        hidden thisType: this
+        hidden thisType2: this
+        """
+          .trimIndent()
+      )
+
+    assertThat(mod.vmClass.isOpen).isTrue
+    mod.getTypeForProperty("moduleType").eq(mod.getTypeForProperty("moduleType2"))
+    mod.getTypeForProperty("moduleType").eq(mod.getTypeForProperty("thisType"))
+    mod.getTypeForProperty("thisType").eq(mod.getTypeForProperty("thisType2"))
+  }
+
+  @Test
+  fun `non-final self - comparison to extended type`(@TempDir tempDir: Path) {
+    val parentPath = tempDir.resolve("parent.pkl")
+    parentPath.writeText(
+      """
+      open module parent
+
+      moduleType: module
+      thisType: this
+      """
+        .trimIndent()
+    )
+
+    val modPath = tempDir.resolve("test.pkl")
+    modPath.writeText(
+      """
+      open module mod
+      extends "parent.pkl"
+      import "parent.pkl" as Parent
+
+      parent: Parent
+      child: Child
+
+      moduleType2: module
+      thisType2: this
+
+      open class Child extends module {
+        // no moduleType3 because module type usage in class bodies is deprecated
+        thisType3: this
+      }
+      """
+        .trimIndent()
+    )
+
+    val mod = makeModule(tempDir, modPath)
+
+    mod.getTypeForProperty("moduleType").eq(mod.getTypeForNestedProperty("parent", "moduleType"))
+    mod.getTypeForProperty("thisType").eq(mod.getTypeForNestedProperty("parent", "moduleType"))
+    mod.getTypeForProperty("moduleType").eq(mod.getTypeForNestedProperty("parent", "thisType"))
+    mod.getTypeForProperty("thisType").eq(mod.getTypeForNestedProperty("parent", "thisType"))
+    mod.getTypeForProperty("moduleType2").sub(mod.getTypeForNestedProperty("parent", "moduleType"))
+    mod.getTypeForProperty("thisType2").sub(mod.getTypeForNestedProperty("parent", "moduleType"))
+    mod.getTypeForProperty("moduleType2").sub(mod.getTypeForNestedProperty("parent", "thisType"))
+    mod.getTypeForProperty("thisType2").sub(mod.getTypeForNestedProperty("parent", "thisType"))
+
+    mod
+      .getTypeForNestedProperty("child", "moduleType")
+      .eq(mod.getTypeForNestedProperty("parent", "moduleType"))
+    mod
+      .getTypeForNestedProperty("child", "thisType")
+      .eq(mod.getTypeForNestedProperty("parent", "moduleType"))
+    mod
+      .getTypeForNestedProperty("child", "moduleType")
+      .eq(mod.getTypeForNestedProperty("parent", "thisType"))
+    mod
+      .getTypeForNestedProperty("child", "thisType")
+      .eq(mod.getTypeForNestedProperty("parent", "thisType"))
+    mod
+      .getTypeForNestedProperty("child", "thisType3")
+      .sub(mod.getTypeForNestedProperty("parent", "moduleType"))
+    mod
+      .getTypeForNestedProperty("child", "thisType3")
+      .sub(mod.getTypeForNestedProperty("parent", "thisType"))
+
+    mod.getTypeForNestedProperty("child", "moduleType").eq(mod.getTypeForProperty("moduleType"))
+    mod.getTypeForNestedProperty("child", "thisType").eq(mod.getTypeForProperty("moduleType"))
+    mod.getTypeForNestedProperty("child", "moduleType").eq(mod.getTypeForProperty("thisType"))
+    mod.getTypeForNestedProperty("child", "thisType").eq(mod.getTypeForProperty("thisType"))
+    mod.getTypeForNestedProperty("child", "thisType3").sub(mod.getTypeForProperty("moduleType2"))
+    mod.getTypeForNestedProperty("child", "thisType3").sub(mod.getTypeForProperty("thisType2"))
+
+    // non-final self type subtype of declared type that is superclass of self type's "base"
+    // class types are never subtypes of non-final self types
+    mod.getTypeForProperty("moduleType").sub(mod.getTypeForProperty("parent"))
+    mod.getTypeForProperty("thisType").sub(mod.getTypeForProperty("parent"))
+    mod.getTypeForProperty("moduleType2").sub(mod.getTypeForProperty("parent"))
+    mod.getTypeForProperty("thisType2").sub(mod.getTypeForProperty("parent"))
+    mod.getTypeForNestedProperty("child", "thisType3").sub(mod.getTypeForProperty("parent"))
+  }
+
+  @Test
+  fun `string literal - equality`() {
+    VmType.StringLiteralType("foo").eq(VmType.StringLiteralType("foo"))
+  }
+
+  @Test
+  fun `string literal - subtype of String`() {
+    VmType.StringLiteralType("foo").sub(VmType.ClassType(BaseModule.getStringClass()))
+  }
+
+  @Test
+  fun `class - equality, unparameterized`() {
+    VmType.ClassType(BaseModule.getBooleanClass())
+      .eq(VmType.ClassType(BaseModule.getBooleanClass()))
+  }
+
+  @Test
+  fun `class - equality, unparameterized generic`() {
+    VmType.ClassType(BaseModule.getListClass()).eq(VmType.ClassType(BaseModule.getListClass()))
+  }
+
+  @Test
+  fun `class - equality, parameterized generic`() {
+    VmType.ClassType(BaseModule.getMappingClass(), stringClass, boolClass)
+      .eq(VmType.ClassType(BaseModule.getMappingClass(), stringClass, boolClass))
+  }
+
+  @Test
+  fun `class - subtype, unparameterized generic`() {
+    VmType.ClassType(BaseModule.getListClass())
+      .sub(VmType.ClassType(BaseModule.getCollectionClass()))
+  }
+
+  @Test
+  fun `class - subtype of any`() {
+    VmType.ClassType(BaseModule.getListClass()).sub(VmType.ClassType(BaseModule.getAnyClass()))
+    VmType.ClassType(BaseModule.getListClass(), stringClass)
+      .sub(VmType.ClassType(BaseModule.getAnyClass()))
+  }
+
+  @Test
+  fun `class - subtype of unparameterized`() {
+    VmType.ClassType(BaseModule.getListClass(), stringClass)
+      .sub(VmType.ClassType(BaseModule.getListClass()))
+  }
+
+  @Test
+  fun `class - subtype, generic with substitution`() {
+    VmType.ClassType(BaseModule.getFunction1Class(), stringClass, boolClass)
+      .sub(VmType.ClassType(BaseModule.getFunctionClass(), boolClass))
+    VmType.ClassType(BaseModule.getFunction1Class(), stringClass, intClass)
+      .sub(VmType.ClassType(BaseModule.getFunctionClass(), numberClass))
+  }
+
+  @Test
+  fun `class - special cases`() {
+    VmType.AliasType(BaseModule.getCharTypeAlias()).sub(stringClass)
+    for (cls in listOf(intClass, numberClass)) {
+      VmType.AliasType(BaseModule.getInt8TypeAlias()).sub(cls)
+      VmType.AliasType(BaseModule.getInt16TypeAlias()).sub(cls)
+      VmType.AliasType(BaseModule.getInt32TypeAlias()).sub(cls)
+      VmType.AliasType(BaseModule.getUIntTypeAlias()).sub(cls)
+      VmType.AliasType(BaseModule.getUInt8TypeAlias()).sub(cls)
+      VmType.AliasType(BaseModule.getUInt16TypeAlias()).sub(cls)
+      VmType.AliasType(BaseModule.getUInt32TypeAlias()).sub(cls)
+    }
+  }
+
+  @Test
+  fun `nullable - class is subtype of nullable class`() {
+    stringClass.sub(VmType.NullableType(stringClass))
+    intClass.sub(VmType.NullableType(numberClass))
+  }
+
+  @Test
+  fun `nullable - subtype of nullable supertype`() {
+    VmType.NullableType(intClass).sub(VmType.NullableType(numberClass))
+  }
+
+  @Test
+  fun `constrained - equality (identity)`() {
+    VmType.ConstrainedType(stringClass, arrayOf("true"), 0)
+      .eq(VmType.ConstrainedType(stringClass, arrayOf("true"), 0))
+  }
+
+  @Test
+  fun `constrained - subtype when base type is supertype`() {
+    VmType.ConstrainedType(stringClass, arrayOf("true"), 0).sub(stringClass)
+    VmType.ConstrainedType(intClass, arrayOf("true"), 0).sub(numberClass)
+  }
+
+  @Test
+  fun `alias - equality`() {
+    val mod =
+      makeModule(
+        """
+        typealias A = Int
+        typealias B = A
+        typealias C = B
+
+        int: Int
+        a: A
+        b: B
+        c: C
+        """
+          .trimIndent()
+      )
+
+    mod.getTypeForProperty("int").eq(mod.getTypeForProperty("a"))
+    mod.getTypeForProperty("int").eq(mod.getTypeForProperty("b"))
+    mod.getTypeForProperty("int").eq(mod.getTypeForProperty("c"))
+    mod.getTypeForProperty("a").eq(mod.getTypeForProperty("b"))
+    mod.getTypeForProperty("a").eq(mod.getTypeForProperty("c"))
+    intClass.eq(mod.getTypeForProperty("b"))
+  }
+
+  @Test
+  fun `alias - subtype`() {
+    val mod =
+      makeModule(
+        """
+        typealias A = Int
+        typealias B = A
+        typealias C = B
+
+        int: Int
+        a: A
+        b: B
+        c: C
+        """
+          .trimIndent()
+      )
+
+    mod.getTypeForProperty("c").sub(numberClass)
+  }
+
+  @Test
+  fun `union - equality (ignores default index)`() {
+    VmType.UnionType(-1, arrayOf("foo", "bar", "baz"))
+      .eq(VmType.UnionType(0, arrayOf("foo", "bar", "baz")))
+  }
+
+  @Test
+  @Disabled("TODO: support order-independent union type equivalence")
+  fun `union - equality, order-independent`() {
+    VmType.UnionType(-1, arrayOf("foo", "bar", "baz"))
+      .eq(VmType.UnionType(-1, arrayOf("bar", "baz", "foo")))
+  }
+
+  @Test
+  fun `union - subtype when all elements are subtype`() {
+    VmType.UnionType(-1, arrayOf("foo", "bar", "baz")).sub(stringClass)
+  }
+
+  @Test
+  fun `union - subtype of union when all elements are contained in supertype`() {
+    VmType.UnionType(-1, arrayOf("foo", "bar", "baz"))
+      .sub(VmType.UnionType(-1, arrayOf("foo", "bar", "baz", "qux")))
+  }
+
+  @Test
+  fun `type variable - treated like unknown, supertype and subtype to all`() {
+    VmType.TypeVariableType(TypeParameter(TypeParameter.Variance.INVARIANT, "Foo", 0))
+      .bidi(stringClass)
+  }
+}