Check if receiver is a module object in relativePathTo (#1650)

Closes #1649

pkl-core/src/main/java/org/pkl/core/stdlib/base/ModuleClassNodes.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.
@@ -15,6 +15,7 @@
  */
 package org.pkl.core.stdlib.base;
 
+import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.dsl.Specialization;
 import java.net.URI;
@@ -30,15 +31,16 @@ public final class ModuleClassNodes {
     @Specialization
     @TruffleBoundary
     protected VmList eval(VmObjectLike self, VmObjectLike other) {
+      if (!self.isModuleObject()) {
+        CompilerDirectives.transferToInterpreter();
+        throw exceptionBuilder().evalError("expectedModuleAsReceiver").build();
+      }
+      if (!other.isModuleObject()) {
+        CompilerDirectives.transferToInterpreter();
+        throw exceptionBuilder().evalError("expectedModuleAsArgument").build();
+      }
       var selfKey = VmUtils.getModuleInfo(self).getModuleKey();
       var selfUri = selfKey.getUri();
-
-      if (!other.isModuleObject()) {
-        throw exceptionBuilder()
-            .evalError("expectedModule")
-            // No meaningful SourceSection available, in this case.
-            .build();
-      }
       var otherKey = VmUtils.getModuleInfo(other).getModuleKey();
       var otherUri = otherKey.getUri();
 

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

@@ -203,7 +203,10 @@ Class `{0}` does not have type parameters.
 notASubclassOfTyped=\
 Class `{0}` is not a subtype of `Typed`.
 
-expectedModule=\
+expectedModuleAsReceiver=\
+Expected a module as the receiver, but got an object that amends a module.
+
+expectedModuleAsArgument=\
 Expected a module as argument, but got an object that amends a module.
 
 wrongTypeArgumentCount=\

pkl-core/src/test/files/LanguageSnippetTests/input/errors/relativePathToNotAModule1.pkl

@@ -0,0 +1,7 @@
+local objectThatAmendsModule = (module) {
+  // add a local property to force this into a new object amends;
+  // empty object amends are optimized away.
+  local qux = 1
+}
+
+res = objectThatAmendsModule.relativePathTo(module)

pkl-core/src/test/files/LanguageSnippetTests/input/errors/relativePathToNotAModule2.pkl

@@ -0,0 +1,8 @@
+local objectThatAmendsModule = (module) {
+  // add a local property to force this into a new object amends;
+  // empty object amends are optimized away.
+  local qux = 1
+}
+
+res = module.relativePathTo(objectThatAmendsModule)
+

pkl-core/src/test/files/LanguageSnippetTests/output/errors/relativePathToNotAModule1.err

@@ -0,0 +1,14 @@
+–– Pkl Error ––
+Expected a module as the receiver, but got an object that amends a module.
+
+x | res = objectThatAmendsModule.relativePathTo(module)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at relativePathToNotAModule1#res (file:///$snippetsDir/input/errors/relativePathToNotAModule1.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/relativePathToNotAModule2.err

@@ -0,0 +1,14 @@
+–– Pkl Error ––
+Expected a module as argument, but got an object that amends a module.
+
+x | res = module.relativePathTo(objectThatAmendsModule)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at relativePathToNotAModule2#res (file:///$snippetsDir/input/errors/relativePathToNotAModule2.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)