Avoid using Object.toString() for in-language API (#1850)

This changes code so that the in-language `toString()` doesn't use
Java's `Object.toString()`.
Additionally, the existing `toString()` implementation is switched over
to using `VmValueRenderer`, which does not force (leaves `?` in place of
unforced values).

This helps improve ergonomics when working on the language (can enable
automatically calling `toString()` on debug values).

Additionally, external tools might call toString(); for example,
Truffle's compiler sometimes will stringify node fields (e.g.
when -Dengine.CompilationFailureAction=Throw) is set.

pkl-core/src/main/java/org/pkl/core/ast/builder/SymbolTable.java

@@ -386,7 +386,7 @@ public final class SymbolTable {
             || value instanceof Boolean
             || value instanceof VmDuration
             || value instanceof VmDataSize) {
-          return "[" + value + "]";
+          return "[" + VmUtils.toPklString(value) + "]";
         }
       }
 

pkl-core/src/main/java/org/pkl/core/ast/internal/ToStringNode.java

@@ -17,7 +17,6 @@ package org.pkl.core.ast.internal;
 
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.dsl.Cached;
-import com.oracle.truffle.api.dsl.Fallback;
 import com.oracle.truffle.api.dsl.Specialization;
 import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.DirectCallNode;
@@ -75,11 +74,10 @@ public abstract class ToStringNode extends UnaryExpressionNode {
     return (String) callNode.call(value, value.getVmClass().getPrototype());
   }
 
-  @Fallback
-  @Override
+  @Specialization
   @TruffleBoundary
-  protected Object fallback(Object value) {
-    return value.toString();
+  protected String evalVmValue(VmValue value) {
+    return value.toPklString();
   }
 
   protected InvokeMethodVirtualNode createInvokeNode() {

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

@@ -119,7 +119,7 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
                 .map((l) -> valueFormatter.formatStringValue(l, ""))
                 .collect(Collectors.joining("|"));
       } else {
-        renderedType = expectedType.toString();
+        renderedType = VmUtils.toPklString(expectedType);
       }
 
       if (actualValue instanceof VmNull
@@ -156,7 +156,10 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
       builder
           .append(
               ErrorMessages.createIndented(
-                  "typeMismatch", indent, renderedType, VmUtils.getClass(actualValue)))
+                  "typeMismatch",
+                  indent,
+                  renderedType,
+                  VmUtils.getClass(actualValue).toPklString()))
           .append("\n")
           .append(indent)
           .append("Value: ")
@@ -177,7 +180,7 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
     public ClassType(SourceSection sourceSection, VmClass actualClass, VmClass expectedClass) {
       super(sourceSection, actualClass);
       this.expectedClass = expectedClass;
-      renderedExpected = "Class<" + expectedClass + ">";
+      renderedExpected = "Class<" + expectedClass.toPklString() + ">";
     }
 
     public ClassType(SourceSection sourceSection, VmClass actualClass, PType expectedType) {
@@ -191,7 +194,7 @@ public abstract class VmTypeMismatchException extends ControlFlowException {
     public void buildMessage(
         AnsiStringBuilder builder, String indent, boolean withPowerAssertions) {
       var actualClass = (VmClass) actualValue;
-      var renderedActualClass = "Class<" + actualClass + ">";
+      var renderedActualClass = "Class<" + actualClass.toPklString() + ">";
 
       // give better error than "expected Class<foo.Bar>, but got Class<foo.Bar>" in case of naming
       // conflict

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

@@ -168,7 +168,7 @@ public final class VmBytes extends VmValue implements Iterable<Long> {
   }
 
   @Override
-  public String toString() {
+  public String toPklString() {
     var sb = new StringBuilder("Bytes(");
     var isFirst = true;
     for (var byt : bytes) {

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

@@ -748,7 +748,7 @@ public final class VmClass extends VmValue {
   }
 
   @Override
-  public String toString() {
+  public String toPklString() {
     return getDisplayName();
   }
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2026 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.
@@ -166,17 +166,19 @@ public abstract class VmCollection extends VmValue implements Iterable<Object> {
 
     var iter = iterator();
     var builder = new StringBuilder();
-    builder.append(iter.next());
+    // TODO: use ToStringNode
+    builder.append(VmUtils.toPklString(iter.next()));
 
     while (iter.hasNext()) {
       builder.append(separator);
-      builder.append(iter.next());
+      builder.append(VmUtils.toPklString(iter.next()));
     }
 
     return builder.toString();
   }
 
-  public final String toString() {
+  @TruffleBoundary
+  public final String toPklString() {
     return VmValueRenderer.multiLine(Integer.MAX_VALUE).render(this);
   }
 }

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

@@ -156,7 +156,7 @@ public final class VmDataSize extends VmValue implements Comparable<VmDataSize>
   }
 
   @Override
-  public String toString() {
+  public String toPklString() {
     return MathUtils.isMathematicalInteger(value) ? (long) value + "." + unit : value + "." + unit;
   }
 

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

@@ -15,6 +15,7 @@
  */
 package org.pkl.core.runtime;
 
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.CompilerDirectives.ValueType;
 import java.util.*;
 import org.jspecify.annotations.Nullable;
@@ -152,7 +153,8 @@ public final class VmDuration extends VmValue implements Comparable<VmDuration>
   }
 
   @Override
-  public String toString() {
+  @TruffleBoundary
+  public String toPklString() {
     return DurationUtils.toPklString(value, unit);
   }
 }

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

@@ -83,7 +83,7 @@ public final class VmDynamic extends VmObject {
 
     iterateAlreadyForcedMemberValues(
         (key, member, value) -> {
-          properties.put(key.toString(), VmValue.export(value));
+          properties.put(VmUtils.toPklString(key), VmValue.export(value));
           return true;
         });
 

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

@@ -199,14 +199,14 @@ public final class VmFunction extends VmObjectLike {
     return System.identityHashCode(this);
   }
 
-  @Override
-  @TruffleBoundary
-  public String toString() {
-    return VmValueRenderer.singleLine(Integer.MAX_VALUE).render(this);
-  }
-
   @Override
   public boolean isParseTimeInvisibleScope() {
     return isFunctionAmend && !hasObjectParams;
   }
+
+  @Override
+  @TruffleBoundary
+  public String toPklString() {
+    return VmValueRenderer.singleLine(Integer.MAX_VALUE).render(this);
+  }
 }

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

@@ -127,7 +127,7 @@ public final class VmIntSeq extends VmValue implements Iterable<Long> {
 
   @Override
   @TruffleBoundary
-  public String toString() {
+  public String toPklString() {
     return step == 1
         ? "IntSeq(" + start + ", " + end + ")"
         : "IntSeq(" + start + ", " + end + ").step(" + step + ")";

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

@@ -286,7 +286,8 @@ public final class VmMap extends VmValue implements Iterable<Map.Entry<Object, O
   }
 
   @TruffleBoundary
-  public String toString() {
+  @Override
+  public String toPklString() {
     return VmValueRenderer.singleLine(Integer.MAX_VALUE).render(this);
   }
 

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

@@ -87,7 +87,7 @@ public final class VmNull extends VmValue {
   }
 
   @Override
-  public String toString() {
+  public String toPklString() {
     return "null";
   }
 }

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

@@ -204,7 +204,8 @@ public abstract class VmObject extends VmObjectLike {
     force(allowUndefinedValues, true);
   }
 
-  public final String toString() {
+  @TruffleBoundary
+  public final String toPklString() {
     force(true, true);
     return VmValueRenderer.singleLine(Integer.MAX_VALUE).render(this);
   }

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

@@ -113,7 +113,7 @@ public final class VmPair extends VmValue implements Iterable<Object> {
 
   @Override
   @TruffleBoundary
-  public String toString() {
+  public String toPklString() {
     force(true);
     return VmValueRenderer.singleLine(Integer.MAX_VALUE).render(this);
   }

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

@@ -539,7 +539,7 @@ public final class VmReference extends VmValue {
   // in-language calls _should_ all go through `ToStringNode`.
   // however, some calls escape through to here currently (e.g. `Listing.join`).
   @Override
-  public String toString() {
+  public String toPklString() {
     var toStringMethod = getVmClass().getDeclaredMethod(Identifier.TO_STRING);
     assert toStringMethod != null;
     var callNode = DirectCallNode.create(toStringMethod.getCallTarget());

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

@@ -77,7 +77,8 @@ public final class VmRegex extends VmValue {
   }
 
   @Override
-  public String toString() {
+  @TruffleBoundary
+  public String toPklString() {
     var builder = new StringBuilder();
     builder.append("Regex(");
     ValueFormatter.withCustomStringDelimiters().formatStringValue(pattern.pattern(), "", builder);

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

@@ -308,7 +308,7 @@ public final class VmTypeAlias extends VmValue {
   }
 
   @Override
-  public String toString() {
+  public String toPklString() {
     return qualifiedName.startsWith("pkl.base#") ? simpleName : qualifiedName;
   }
 

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

@@ -98,7 +98,7 @@ public final class VmUndefinedValueException extends VmEvalException {
         }
         builder.append(Lexer.maybeQuoteIdentifier(pathPart.toString()));
       } else {
-        builder.append('[').append(pathPart).append(']');
+        builder.append('[').append(VmUtils.toPklString(pathPart)).append(']');
       }
     }
   }

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

@@ -1125,6 +1125,18 @@ public final class VmUtils {
     return value;
   }
 
+  public static String toPklString(Object value) {
+    if (value instanceof VmValue vmValue) {
+      return vmValue.toPklString();
+    }
+    return toString(value);
+  }
+
+  @TruffleBoundary
+  private static String toString(Object value) {
+    return value.toString();
+  }
+
   public static boolean isPklBug(VmStackOverflowException e) {
     // There's no good way to tell if a StackOverflowError came from Pkl, or from our
     // implementation.

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

@@ -15,9 +15,12 @@
  */
 package org.pkl.core.runtime;
 
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import org.jspecify.annotations.Nullable;
 
 public abstract class VmValue {
+  private final VmValueRenderer vmValueRenderer = VmValueRenderer.multiLine(Integer.MAX_VALUE);
+
   public abstract VmClass getVmClass();
 
   public VmTyped getPrototype() {
@@ -90,4 +93,16 @@ public abstract class VmValue {
   /** Enables calling `vmValue.equals()` when not behind a Truffle boundary. */
   @Override
   public abstract boolean equals(Object obj);
+
+  @TruffleBoundary
+  public abstract String toPklString();
+
+  /**
+   * Override default implementation because it calls {@link #hashCode()}, which will do object eval
+   * on certain types.
+   */
+  @Override
+  public final String toString() {
+    return vmValueRenderer.render(this);
+  }
 }

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

@@ -111,12 +111,12 @@ public final class VmValueRenderer {
 
     @Override
     public void visitDuration(VmDuration value) {
-      append(value);
+      append(value.toPklString());
     }
 
     @Override
     public void visitDataSize(VmDataSize value) {
-      append(value);
+      append(value.toPklString());
     }
 
     private void renderByteSize(VmDataSize size) {
@@ -169,12 +169,12 @@ public final class VmValueRenderer {
 
     @Override
     public void visitRegex(VmRegex value) {
-      append(value);
+      append(value.toPklString());
     }
 
     @Override
     public void visitIntSeq(VmIntSeq value) {
-      append(value);
+      append(value.toPklString());
     }
 
     @Override
@@ -258,12 +258,12 @@ public final class VmValueRenderer {
 
     @Override
     public void visitClass(VmClass value) {
-      append(value);
+      append(value.toPklString());
     }
 
     @Override
     public void visitTypeAlias(VmTypeAlias value) {
-      append(value);
+      append(value.toPklString());
     }
 
     @Override
@@ -296,7 +296,7 @@ public final class VmValueRenderer {
     }
 
     private void append(Object value) {
-      builder.append(value);
+      builder.append(VmUtils.toPklString(value));
       checkLengthLimit();
     }
 

pkl-core/src/main/java/org/pkl/core/stdlib/base/AnyNodes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2026 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.
@@ -38,10 +38,16 @@ public final class AnyNodes {
   }
 
   public abstract static class toString extends ExternalMethod0Node {
+    @Specialization
+    @TruffleBoundary
+    protected String evalString(VmValue vmValue) {
+      return vmValue.toPklString();
+    }
+
     @Specialization
     @TruffleBoundary
     protected String evalString(Object self) {
-      return self.toString();
+      return VmUtils.toPklString(self);
     }
   }
 
@@ -50,7 +56,7 @@ public final class AnyNodes {
 
     @Specialization
     @SuppressWarnings("UnusedParameters")
-    protected VmNull eval(VmNull self, VmFunction function) {
+    protected VmNull eval(VmNull self, VmFunction ignored) {
       return self;
     }
 

pkl-core/src/main/java/org/pkl/core/stdlib/base/JsonRendererNodes.java

@@ -93,7 +93,9 @@ public final class JsonRendererNodes {
     @Override
     public void visitFloat(Double value) {
       if (value.isNaN() || value.isInfinite()) {
-        throw new VmExceptionBuilder().evalError("cannotRenderValue", value, name).build();
+        throw new VmExceptionBuilder()
+            .evalError("cannotRenderValue", VmUtils.toPklString(value), name)
+            .build();
       }
       builder.append((double) value);
     }

pkl-core/src/main/java/org/pkl/core/stdlib/base/ListingNodes.java

@@ -292,7 +292,8 @@ public final class ListingNodes {
             if (!key.equals(0L)) {
               builder.append(separator);
             }
-            builder.append(value);
+            // TODO: use ToStringNode
+            builder.append(VmUtils.toPklString(value));
             return true;
           });
       LoopNode.reportLoopCount(this, self.getLength());

pkl-core/src/main/java/org/pkl/core/stdlib/base/PcfRenderer.java

@@ -92,17 +92,17 @@ public final class PcfRenderer extends AbstractStringRenderer {
 
   @Override
   public void visitDuration(VmDuration value) {
-    builder.append(value);
+    builder.append(value.toPklString());
   }
 
   @Override
   public void visitDataSize(VmDataSize value) {
-    builder.append(value);
+    builder.append(value.toPklString());
   }
 
   @Override
   public void visitBytes(VmBytes value) {
-    builder.append(value);
+    builder.append(value.toPklString());
   }
 
   @Override
@@ -116,12 +116,12 @@ public final class PcfRenderer extends AbstractStringRenderer {
 
   @Override
   public void visitRegex(VmRegex value) {
-    builder.append(value);
+    builder.append(value.toPklString());
   }
 
   @Override
   public void visitIntSeq(VmIntSeq value) {
-    builder.append(value);
+    builder.append(value.toPklString());
   }
 
   @Override

pkl-core/src/main/java/org/pkl/core/stdlib/base/PropertiesRendererNodes.java

@@ -307,7 +307,7 @@ public final class PropertiesRendererNodes {
                 } else {
                   builder.append(
                       PropertiesUtils.renderPropertiesKeyOrValue(
-                          path.toString(), true, restrictCharset));
+                          VmUtils.toPklString(path), true, restrictCharset));
                 }
                 isFollowing.set(true);
               });

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

@@ -534,31 +534,31 @@ public final class RendererNodes {
     @Override
     public void visitIntSeq(VmIntSeq value) {
       writePropertyName();
-      builder.append(value);
+      builder.append(value.toPklString());
     }
 
     @Override
     public void visitPair(VmPair value) {
       writePropertyName();
-      builder.append(value);
+      builder.append(value.toPklString());
     }
 
     @Override
     public void visitRegex(VmRegex value) {
       writePropertyName();
-      builder.append(value);
+      builder.append(value.toPklString());
     }
 
     @Override
     public void visitNull(VmNull value) {
       writePropertyName();
-      builder.append(value);
+      builder.append(value.toPklString());
     }
 
     @Override
     public void visitReference(VmReference value) {
       writePropertyName();
-      builder.append(value);
+      builder.append(value.toPklString());
     }
 
     /**

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

@@ -508,4 +508,9 @@ examples {
     List(1, "Pigeon", 3.d).reverse()
     List().reverse()
   }
+
+  ["join()"] {
+    List(1.s, 2.s).join(", ")
+    List(1.mb, 2.gb).join(", ")
+  }
 }

pkl-core/src/test/files/LanguageSnippetTests/input/api/propertiesRenderer13.properties.pkl

@@ -0,0 +1,4 @@
+output {
+  value = Map(5.s, "value")
+  renderer = new PropertiesRenderer {}
+}

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

@@ -440,4 +440,9 @@ examples {
     Set(1, "Pigeon", 3.d).reverse()
     Set().reverse()
   }
+
+  ["join()"] {
+    Set(1.s, 2.s).join(", ")
+    Set(1.mb, 2.gb).join(", ")
+  }
 }

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

@@ -0,0 +1,3 @@
+one {
+  [5.mb] = throw("ouch")
+}

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

@@ -0,0 +1,3 @@
+one {
+  [5.s] = throw("ouch")
+}

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

@@ -438,4 +438,8 @@ examples {
     List(3.d, "Pigeon", 1)
     List()
   }
+  ["join()"] {
+    "1.s, 2.s"
+    "1.mb, 2.gb"
+  }
 }

pkl-core/src/test/files/LanguageSnippetTests/output/api/propertiesRenderer13.properties

@@ -0,0 +1 @@
+5.s = value

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

@@ -377,4 +377,8 @@ examples {
     List(3.d, "Pigeon", 1)
     List()
   }
+  ["join()"] {
+    "1.s, 2.s"
+    "1.mb, 2.gb"
+  }
 }

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

@@ -0,0 +1,14 @@
+–– Pkl Error ––
+ouch
+
+x | [5.mb] = throw("ouch")
+             ^^^^^^^^^^^^^
+at stackTraceWithDataSizeEntryName#one[5.mb] (file:///$snippetsDir/input/errors/stackTraceWithDataSizeEntryName.pkl)
+
+xxx | renderer.renderDocument(value)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at pkl.base#Module.output.text (pkl:base)
+
+xxx | if (renderer is BytesRenderer) renderer.renderDocument(value) else text.encodeToBytes("UTF-8")
+                                                                         ^^^^
+at pkl.base#Module.output.bytes (pkl:base)

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

@@ -0,0 +1,14 @@
+–– Pkl Error ––
+ouch
+
+x | [5.s] = throw("ouch")
+            ^^^^^^^^^^^^^
+at stackTraceWithDurationEntryName#one[5.s] (file:///$snippetsDir/input/errors/stackTraceWithDurationEntryName.pkl)
+
+xxx | renderer.renderDocument(value)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at pkl.base#Module.output.text (pkl:base)
+
+xxx | if (renderer is BytesRenderer) renderer.renderDocument(value) else text.encodeToBytes("UTF-8")
+                                                                         ^^^^
+at pkl.base#Module.output.bytes (pkl:base)

pkl-core/src/test/kotlin/org/pkl/core/EvaluatorTest.kt

@@ -94,6 +94,13 @@ class EvaluatorTest {
     checkModule(module)
   }
 
+  @Test
+  fun `evaluate text with dynamic entry keyed by a non-identifier value`() {
+    val module = evaluator.evaluate(text("""result = new Dynamic { [5.s] = "value" }"""))
+    val result = module.getProperty("result") as PObject
+    assertThat(result.properties).containsEntry("5.s", "value")
+  }
+
   @Test
   fun `evaluate text with relative import`() {
     val e = assertThrows<PklException> { evaluator.evaluate(text("import \"foo.bar\"")) }

pkl-core/src/test/kotlin/org/pkl/core/util/ErrorMessagesTest.kt

@@ -42,7 +42,7 @@ class ErrorMessagesTest {
 
     override fun equals(obj: Any?): Boolean = this === obj
 
-    override fun toString(): String {
+    override fun toPklString(): String {
       force(true)
       return "lazy"
     }