Enforce that abstract members are implemented

This adds a check that abstract members must be implemented.
If any members lack an implementation, an error is thrown describing
the missing members.

Also: we have a bug in `pkl:base`; class `Set` does not implement all
members of class `Collection`.

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

@@ -24,7 +24,7 @@ import org.pkl.core.ast.VmModifier;
 import org.pkl.core.runtime.*;
 
 public final class ClassProperty extends ClassMember {
-  private final @Nullable PropertyTypeNode typeNode;
+  private @Nullable PropertyTypeNode typeNode;
   private final ObjectMember initializer;
 
   public ClassProperty(
@@ -64,6 +64,11 @@ public final class ClassProperty extends ClassMember {
     return VmModifier.getMirrors(mods, false);
   }
 
+  public void lateInitTypeNodeAndModifiers(@Nullable PropertyTypeNode typeNode, int modifiers) {
+    this.typeNode = typeNode;
+    this.modifiers = modifiers;
+  }
+
   public @Nullable PropertyTypeNode getTypeNode() {
     return typeNode;
   }

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

@@ -25,7 +25,7 @@ public abstract class Member {
 
   protected final SourceSection headerSection;
 
-  protected final int modifiers;
+  protected int modifiers;
 
   protected final @Nullable Identifier name;
 

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

@@ -22,6 +22,7 @@ import com.oracle.truffle.api.dsl.Idempotent;
 import com.oracle.truffle.api.frame.FrameDescriptor;
 import com.oracle.truffle.api.source.SourceSection;
 import java.util.*;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.*;
 import org.graalvm.collections.*;
 import org.jspecify.annotations.Nullable;
@@ -84,6 +85,13 @@ public final class VmClass extends VmValue {
 
   private final Object allHiddenPropertyNamesLock = new Object();
 
+  @GuardedBy("finalizersLock")
+  private @Nullable List<Runnable> __finalizers = null;
+
+  private final Object finalizersLock = new Object();
+
+  private final AtomicInteger uninitializedSuperclassCount = new AtomicInteger(0);
+
   // Helps to overcome recursive initialization issues
   // between classes and annotations in pkl.base.
   @CompilationFinal private volatile boolean isInitialized;
@@ -150,6 +158,83 @@ public final class VmClass extends VmValue {
     prototype.lateInitParent(superclass.getPrototype());
   }
 
+  @TruffleBoundary
+  private void checkAbstractMembers() {
+    if (this.isAbstract()) return;
+    // minimize allocations in the non-error case
+    if (!hasAbstractMember()) return;
+    var abstractMembers = getAbstractMembers();
+    if (abstractMembers.size() == 1) {
+      var member = abstractMembers.get(0);
+      var message =
+          member instanceof ClassProperty
+              ? "noImplementationForAbstractProperty"
+              : "noImplementationForAbstractMethod";
+      throw new VmExceptionBuilder()
+          .evalError(message, getDisplayName(), member.getName().toString())
+          .withSourceSection(getHeaderSection())
+          .build();
+    }
+    var memberList = new StringBuilder();
+    var isFirst = true;
+    for (var member : abstractMembers) {
+      if (isFirst) {
+        isFirst = false;
+      } else {
+        memberList.append('\n');
+      }
+      memberList.append("* ");
+      if (member instanceof ClassProperty) {
+        memberList.append("property ");
+      } else {
+        memberList.append("method ");
+      }
+      memberList.append('`').append(member.getName()).append('`');
+    }
+    throw new VmExceptionBuilder()
+        .evalError("noImplementationForAbstractMembers", getDisplayName(), memberList.toString())
+        .withSourceSection(getHeaderSection())
+        .build();
+  }
+
+  private boolean hasAbstractMember() {
+    var propertyCursor = getAllProperties().getEntries();
+    while (propertyCursor.advance()) {
+      var property = propertyCursor.getValue();
+      if (property.isAbstract()) {
+        return true;
+      }
+    }
+    var methodCursor = getAllMethods().getEntries();
+    while (methodCursor.advance()) {
+      var method = methodCursor.getValue();
+      if (method.isAbstract()) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  private List<ClassMember> getAbstractMembers() {
+    assert this.superclass != null;
+    var result = new ArrayList<ClassMember>();
+    var propertyCursor = getAllProperties().getEntries();
+    while (propertyCursor.advance()) {
+      var property = propertyCursor.getValue();
+      if (property.isAbstract()) {
+        result.add(property);
+      }
+    }
+    var methodCursor = getAllMethods().getEntries();
+    while (methodCursor.advance()) {
+      var method = methodCursor.getValue();
+      if (method.isAbstract()) {
+        result.add(method);
+      }
+    }
+    return result;
+  }
+
   @TruffleBoundary
   public void addProperty(ClassProperty property) {
     prototype.addProperty(property.getInitializer());
@@ -190,8 +275,46 @@ public final class VmClass extends VmValue {
     }
   }
 
+  private void onInitialized(Runnable runnable) {
+    synchronized (finalizersLock) {
+      if (this.__finalizers == null) {
+        this.__finalizers = new ArrayList<>();
+      }
+      this.__finalizers.add(runnable);
+    }
+  }
+
   // Note: Superclasses may not have finished their initialization when this method is called.
   public void notifyInitialized() {
+    var sc = superclass;
+    var isAllInitialized = true;
+    var uninitializedCount = 0;
+    while (sc != null) {
+      if (!sc.isInitialized) {
+        sc.onInitialized(
+            () -> {
+              var count = uninitializedSuperclassCount.decrementAndGet();
+              if (count == 0) {
+                checkAbstractMembers();
+              }
+            });
+        uninitializedCount++;
+        isAllInitialized = false;
+      }
+      sc = sc.superclass;
+    }
+    uninitializedSuperclassCount.set(uninitializedCount);
+    if (isAllInitialized) {
+      checkAbstractMembers();
+    }
+    lock:
+    synchronized (finalizersLock) {
+      if (__finalizers == null) break lock;
+      for (var finalizer : __finalizers) {
+        finalizer.run();
+      }
+      this.__finalizers = null;
+    }
     isInitialized = true;
   }
 
@@ -735,13 +858,27 @@ public final class VmClass extends VmValue {
     for (var property : EconomicMaps.getValues(declaredProperties)) {
       if (property.isLocal()) continue;
 
-      // A property is considered a class property definition
-      // if it has a type annotation or has no superdefinition (ad-hoc case).
+      // A property is considered a class property definition if any of the following are true:
+      //
+      // 1. It has a type annotation.
+      // 2. It has no superdefinition.
+      // 3. It is not abstract but its superclass is.
+      //
       // Otherwise, it is considered an object property definition,
       // which means it affects the class prototype but not the class itself.
       // An example for the latter is when `Module.output` is overridden with `output { ... }`.
-      if (property.getTypeNode() != null || !EconomicMaps.containsKey(result, property.getName())) {
+      if (property.getTypeNode() != null) {
         EconomicMaps.put(result, property.getName(), property);
+      } else {
+        var existingProperty = EconomicMaps.get(result, property.getName());
+        if (existingProperty != null && existingProperty.isAbstract() && !this.isAbstract()) {
+          property.lateInitTypeNodeAndModifiers(
+              existingProperty.getTypeNode(),
+              existingProperty.getModifiers() & ~VmModifier.ABSTRACT);
+          EconomicMaps.put(result, property.getName(), property);
+        } else if (existingProperty == null) {
+          EconomicMaps.put(result, property.getName(), property);
+        }
       }
     }
 

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

@@ -1176,3 +1176,13 @@ Cannot follow redirect from ''https:'' URL to ''http:'' URL.\
 \n\
 HTTP Request: `GET {0}`\n\
 Redirected to: `{1}`
+
+noImplementationForAbstractProperty=\
+Class `{0}` should either be declared `abstract`, or should implement property `{1}`.
+
+noImplementationForAbstractMethod=\
+Class `{0}` should either be declared `abstract`, or should implement method `{1}`.
+
+noImplementationForAbstractMembers=\
+Class `{0}` should either be declared `abstract`, or implement the following members:\n\
+{1}

pkl-core/src/test/files/LanguageSnippetTests/input-helper/classes/AbstractModule.pkl

@@ -0,0 +1,3 @@
+abstract module Foo
+
+abstract bar: Int

pkl-core/src/test/files/LanguageSnippetTests/input/errors/abstractMemberNotImplemented1.pkl

@@ -0,0 +1,19 @@
+abstract class AbstractProperty {
+  abstract foo: Int
+}
+
+abstract class AbstractMethod {
+  abstract function foo(): Int
+}
+
+abstract class AbstractPropertiesAndMethods {
+  abstract foo: Int
+  abstract bar: Int
+  abstract function foo(): Int
+  abstract function bar(): Int
+}
+
+class MyClass extends AbstractProperty {
+}
+
+foo: MyClass

pkl-core/src/test/files/LanguageSnippetTests/input/errors/abstractMemberNotImplemented2.pkl

@@ -0,0 +1,9 @@
+abstract class AbstractMethod {
+  abstract function foo(): Int
+}
+
+class MyClass extends AbstractMethod {
+}
+
+foo: MyClass
+

pkl-core/src/test/files/LanguageSnippetTests/input/errors/abstractMemberNotImplemented3.pkl

@@ -0,0 +1,10 @@
+abstract class AbstractPropertiesAndMethods {
+  abstract foo: Int
+  abstract bar: Int
+  abstract function foo(): Int
+  abstract function bar(): Int
+}
+
+class MyClass extends AbstractPropertiesAndMethods {}
+
+foo: MyClass

pkl-core/src/test/files/LanguageSnippetTests/input/errors/abstractMemberNotImplemented4.pkl

@@ -0,0 +1 @@
+extends "../../input-helper/classes/AbstractModule.pkl"

pkl-core/src/test/files/LanguageSnippetTests/output/errors/abstractMemberNotImplemented1.err

@@ -0,0 +1,10 @@
+–– Pkl Error ––
+Class `abstractMemberNotImplemented1#MyClass` should either be declared `abstract`, or should implement property `foo`.
+
+xx | class MyClass extends AbstractProperty {
+     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at abstractMemberNotImplemented1#MyClass (file:///$snippetsDir/input/errors/abstractMemberNotImplemented1.pkl)
+
+xx | foo: MyClass
+          ^^^^^^^
+at abstractMemberNotImplemented1 (file:///$snippetsDir/input/errors/abstractMemberNotImplemented1.pkl)

pkl-core/src/test/files/LanguageSnippetTests/output/errors/abstractMemberNotImplemented2.err

@@ -0,0 +1,10 @@
+–– Pkl Error ––
+Class `abstractMemberNotImplemented2#MyClass` should either be declared `abstract`, or should implement method `foo`.
+
+x | class MyClass extends AbstractMethod {
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at abstractMemberNotImplemented2#MyClass (file:///$snippetsDir/input/errors/abstractMemberNotImplemented2.pkl)
+
+x | foo: MyClass
+         ^^^^^^^
+at abstractMemberNotImplemented2 (file:///$snippetsDir/input/errors/abstractMemberNotImplemented2.pkl)

pkl-core/src/test/files/LanguageSnippetTests/output/errors/abstractMemberNotImplemented3.err

@@ -0,0 +1,14 @@
+–– Pkl Error ––
+Class `abstractMemberNotImplemented3#MyClass` should either be declared `abstract`, or implement the following members:
+* property `foo`
+* property `bar`
+* method `foo`
+* method `bar`
+
+x | class MyClass extends AbstractPropertiesAndMethods {}
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at abstractMemberNotImplemented3#MyClass (file:///$snippetsDir/input/errors/abstractMemberNotImplemented3.pkl)
+
+xx | foo: MyClass
+          ^^^^^^^
+at abstractMemberNotImplemented3 (file:///$snippetsDir/input/errors/abstractMemberNotImplemented3.pkl)

pkl-core/src/test/files/LanguageSnippetTests/output/errors/abstractMemberNotImplemented4.err

@@ -0,0 +1,6 @@
+–– Pkl Error ––
+Class `abstractMemberNotImplemented4` should either be declared `abstract`, or should implement property `bar`.
+
+x | extends "../../input-helper/classes/AbstractModule.pkl"
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at abstractMemberNotImplemented4 (file:///$snippetsDir/input/errors/abstractMemberNotImplemented4.pkl)

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

@@ -0,0 +1,10 @@
+–– Pkl Error ––
+Class `abstractMethodsNotImplemented#MyClass` either needs to be abstract, or should implement property `foo`.
+
+x | class MyClass extends MyAbstractClass {
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at abstractMethodsNotImplemented#MyClass (file:///$snippetsDir/input/errors/abstractMethodsNotImplemented.pkl)
+
+x | foo: MyClass
+         ^^^^^^^
+at abstractMethodsNotImplemented (file:///$snippetsDir/input/errors/abstractMethodsNotImplemented.pkl)

stdlib/base.pkl

@@ -3562,6 +3562,18 @@ external class Set<out Element> extends Collection<Element> {
 
   /// The difference of this set and [other].
   external function difference(other: Set): Set<Element>
+
+  function indexOf(_): Int = throw("Set does not implement `indexOf`")
+  function indexOfOrNull(_): Int? = throw("Set does not implement `indexOfOrNull`")
+
+  function lastIndexOf(_): Int = throw("Set does not implement `lastIndexOf`")
+  function lastIndexOfOrNull(_): Int? = throw("Set does not implement `lastIndexOfOrNull`")
+
+  function findIndex(_): Int = throw("Set does not implement `findIndex`")
+  function findIndexOrNull(_): Int? = throw("Set does not implement `findIndexOrNull`")
+
+  function findLastIndex(_): Int = throw("Set does not implement `findLastIndex`")
+  function findLastIndexOrNull(_): Int? = throw("Set does not implement `findLastIndexOrNull`")
 }
 
 /// Creates a map containing the given alternating [keysAndValues].