Add import destructuring and amends/extends of classes within modules

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

@@ -1325,11 +1325,22 @@ public PklRootNode visitModule(Module mod) {
 
     var extendsOrAmendsClause = moduleDecl != null ? moduleDecl.getExtendsOrAmendsDecl() : null;
 
-    var supermoduleNode =
-        extendsOrAmendsClause == null
-            ? resolveBaseModuleClass(
-                org.pkl.core.runtime.Identifier.MODULE, BaseModule::getModuleClass)
-            : doVisitImport(false, extendsOrAmendsClause, extendsOrAmendsClause.getUrl());
+    ExpressionNode supermoduleNode;
+    if (extendsOrAmendsClause == null) {
+      supermoduleNode =
+          resolveBaseModuleClass(
+              org.pkl.core.runtime.Identifier.MODULE, BaseModule::getModuleClass);
+    } else {
+      supermoduleNode = doVisitImport(false, extendsOrAmendsClause, extendsOrAmendsClause.getUrl());
+      if (extendsOrAmendsClause.getParentTypeName() != null) {
+        supermoduleNode =
+            ReadPropertyNodeGen.create(
+                createSourceSection(extendsOrAmendsClause),
+                org.pkl.core.runtime.Identifier.get(
+                    extendsOrAmendsClause.getParentTypeName().getValue()),
+                supermoduleNode);
+      }
+    }
 
     var propertyNames =
         CollectionUtils.<String>newHashSet(
@@ -1421,9 +1432,12 @@ private EconomicMap<Object, ObjectMember> doVisitModuleProperties(
     var result = EconomicMaps.<Object, ObjectMember>create(totalSize);
 
     for (var _import : imports) {
-      var member = visitImportClause(_import);
-      checkDuplicateMember(member.getName(), member.getHeaderSection(), propertyNames);
-      EconomicMaps.put(result, member.getName(), member);
+      visitImportClause(_import)
+          .forEach(
+              (member) -> {
+                checkDuplicateMember(member.getName(), member.getHeaderSection(), propertyNames);
+                EconomicMaps.put(result, member.getName(), member);
+              });
     }
 
     for (var clazz : classes) {
@@ -1479,36 +1493,76 @@ private EconomicMap<Object, ObjectMember> doVisitModuleProperties(
   }
 
   @Override
-  public ObjectMember visitImportClause(ImportClause imp) {
+  public List<ObjectMember> visitImportClause(ImportClause imp) {
     var importNode = doVisitImport(imp.isGlob(), imp, imp.getImportStr());
     var moduleKey = moduleResolver.resolve(importNode.getImportUri());
     var importName =
         org.pkl.core.runtime.Identifier.property(
             imp.getAlias() != null ? imp.getAlias().getValue() : IoUtils.inferModuleName(moduleKey),
             true);
 
-    return symbolTable.enterProperty(
-        importName,
-        ConstLevel.NONE,
-        scope -> {
-          var modifiers = VmModifier.IMPORT | VmModifier.LOCAL | VmModifier.CONST;
-          if (imp.isGlob()) {
-            modifiers = modifiers | VmModifier.GLOB;
-          }
-          var result =
-              new ObjectMember(
-                  importNode.getSourceSection(),
-                  importNode.getSourceSection(),
-                  modifiers,
-                  scope.getName(),
-                  scope.getQualifiedName());
-
-          result.initMemberNode(
-              new UntypedObjectMemberNode(
-                  language, scope.buildFrameDescriptor(), result, importNode));
+    var imports =
+        new ArrayList<ObjectMember>(
+            1
+                + (imp.getDeconstructions() != null
+                    ? imp.getDeconstructions().getDeconstructions().size()
+                    : 0));
+    imports.add(
+        symbolTable.enterProperty(
+            importName,
+            ConstLevel.NONE,
+            scope -> handleImportClauseItem(imp, importNode, null, scope)));
+
+    if (imp.getDeconstructions() == null) return imports;
+    assert !imp.isGlob();
+    for (var deconstruction : imp.getDeconstructions().getDeconstructions()) {
+      var deconstructionName =
+          org.pkl.core.runtime.Identifier.property(
+              deconstruction.getAlias() != null
+                  ? deconstruction.getAlias().getValue()
+                  : deconstruction.getName().getValue(),
+              true);
+      imports.add(
+          symbolTable.enterProperty(
+              deconstructionName,
+              ConstLevel.NONE,
+              scope ->
+                  handleImportClauseItem(
+                      imp,
+                      importNode,
+                      org.pkl.core.runtime.Identifier.get(deconstruction.getName().getValue()),
+                      scope)));
+    }
+    return imports;
+  }
+
+  private ObjectMember handleImportClauseItem(
+      ImportClause imp,
+      AbstractImportNode importNode,
+      @Nullable org.pkl.core.runtime.Identifier memberName,
+      SymbolTable.PropertyScope scope) {
+    var modifiers = VmModifier.IMPORT | VmModifier.LOCAL | VmModifier.CONST;
+    if (imp.isGlob()) {
+      modifiers = modifiers | VmModifier.GLOB;
+    }
+    var result =
+        new ObjectMember(
+            importNode.getSourceSection(),
+            importNode.getSourceSection(),
+            modifiers,
+            scope.getName(),
+            scope.getQualifiedName());
+
+    result.initMemberNode(
+        new UntypedObjectMemberNode(
+            language,
+            scope.buildFrameDescriptor(),
+            result,
+            memberName == null
+                ? importNode
+                : ReadPropertyNodeGen.create(createSourceSection(imp), memberName, importNode)));
 
-          return result;
-        });
+    return result;
   }
 
   @Override

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

@@ -25,6 +25,7 @@
 import org.pkl.core.ast.member.ObjectMember;
 import org.pkl.core.ast.type.UnresolvedTypeNode;
 import org.pkl.core.runtime.ModuleInfo;
+import org.pkl.core.runtime.VmClass;
 import org.pkl.core.runtime.VmLanguage;
 import org.pkl.core.runtime.VmTyped;
 import org.pkl.core.runtime.VmUtils;
@@ -78,4 +79,10 @@ protected VmTyped eval(VirtualFrame frame, VmTyped supermodule) {
 
     return module;
   }
+
+  // when using `amends Foo in "bar.pkl"`
+  @Specialization
+  protected VmTyped eval(VirtualFrame frame, VmClass superclass) {
+    return eval(frame, superclass.getPrototype());
+  }
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024-2025 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.
@@ -191,13 +191,17 @@ public TypeNode execute(VirtualFrame frame) {
         return new TypeAliasTypeNode(sourceSection, alias, new TypeNode[0]);
       }
 
-      var module = (VmTyped) type;
-      assert module.isModuleObject();
-      var clazz = module.getVmClass();
-      if (!module.isPrototype()) {
-        throw exceptionBuilder().evalError("notAModuleType", clazz.getModuleName()).build();
+      var moduleOrClass = (VmTyped) type;
+      var clazz = moduleOrClass.getVmClass();
+      if (!moduleOrClass.isPrototype()) {
+        throw exceptionBuilder()
+            .evalError(
+                "notAModuleOrClassType",
+                moduleOrClass.isModuleObject() ? "Module" : "Class",
+                clazz.getDisplayName())
+            .build();
       }
-      return TypeNode.forClass(sourceSection, module.getVmClass());
+      return TypeNode.forClass(sourceSection, clazz);
     }
   }
 

pkl-core/src/main/java/org/pkl/core/repl/ReplServer.java

@@ -222,7 +222,7 @@ private List<Object> evaluate(
           var exprNode = builder.visitExpr(expr);
           evaluateExpr(replState, exprNode, forceResults, results);
         } else if (tree instanceof ImportClause importClause) {
-          addStaticModuleProperty(builder.visitImportClause(importClause));
+          builder.visitImportClause(importClause).forEach(this::addStaticModuleProperty);
         } else if (tree instanceof ClassProperty classProperty) {
           var propertyNode = builder.visitClassProperty(classProperty);
           var property = addModuleProperty(propertyNode);

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

@@ -49,8 +49,8 @@ Cannot invoke abstract property `{0}`.
 cannotInvokeSupermethodFromHere=\
 Cannot invoke a supermethod from here.
 
-notAModuleType=\
-Module `{0}` cannot be extended or used as type because it amends another module.
+notAModuleOrClassType=\
+{0} `{1}` cannot be extended or used as type because it amends another module or class.
 
 invalidSupertype=\
 `{0}` is not a valid supertype.

pkl-core/src/test/files/LanguageSnippetTests/input-helper/modules/amendModuleClass.pkl

@@ -0,0 +1,3 @@
+amends Widget in ".../input/basic/imported.pkl"
+
+qux = 5

pkl-core/src/test/files/LanguageSnippetTests/input-helper/modules/amendModuleValue.pkl

@@ -0,0 +1,3 @@
+amends baz in ".../input/basic/imported.pkl"
+
+qux = 5

pkl-core/src/test/files/LanguageSnippetTests/input-helper/modules/extendModuleClass.pkl

@@ -0,0 +1,3 @@
+extends Widget in ".../input/basic/imported.pkl"
+
+corge = quux * qux

pkl-core/src/test/files/LanguageSnippetTests/input-helper/modules/extendModuleValue.pkl

@@ -0,0 +1 @@
+extends baz in ".../input/basic/imported.pkl"

pkl-core/src/test/files/LanguageSnippetTests/input/basic/import4.pkl

@@ -0,0 +1,15 @@
+import "imported.pkl" as _imported, { Widget as _Widget, baz }
+import "imported2.pkl" as imported2, { baz as qux, bax as quux }
+import "pkl:test"
+
+a = _imported
+b: _imported = new {
+  foo = 7
+}
+c = baz
+d: _Widget = new {
+  qux = 5
+}
+e = test.catch(() -> new baz {}) // TODO provide a better error here than an assertion failure
+f = test.catch(() -> new qux {}) // TODO provide a better error here than an assertion failure
+g = test.catch(() -> new imported2 {}) // TODO provide a better error here than an assertion failure

pkl-core/src/test/files/LanguageSnippetTests/input/basic/import5.pkl

@@ -0,0 +1,5 @@
+import "imported.pkl" as { Widget as _Widget }
+
+class _Widget {}
+
+a = new _Widget {}

pkl-core/src/test/files/LanguageSnippetTests/input/basic/imported.pkl

@@ -1,2 +1,11 @@
 foo = bar * 2
 bar = 3
+
+open class Widget {
+  qux: Int
+  quux: Int = qux * 3
+}
+
+baz: Widget = new {
+  qux = 4
+}

pkl-core/src/test/files/LanguageSnippetTests/input/basic/imported2.pkl

@@ -0,0 +1 @@
+amends "imported.pkl"

pkl-core/src/test/files/LanguageSnippetTests/input/modules/amendModule7.pkl

@@ -0,0 +1,4 @@
+// these don't extend Module so they have no `output` property
+// thus cannot be rendered directly
+amendModuleClass = import(".../input-helper/modules/amendModuleClass.pkl")
+amendModuleValue = import(".../input-helper/modules/amendModuleValue.pkl")

pkl-core/src/test/files/LanguageSnippetTests/input/modules/extendModule2.pkl

@@ -0,0 +1,8 @@
+import "pkl:test"
+
+// these don't extend Module so they have no `output` property
+// thus cannot be rendered directly
+extendModuleClass = (import(".../input-helper/modules/extendModuleClass.pkl")) {
+  qux = 2
+}
+extendModuleValue = test.catch(() -> import(".../input-helper/modules/extendModuleValue.pkl"))

pkl-core/src/test/files/LanguageSnippetTests/output/basic/import4.pcf

@@ -0,0 +1,27 @@
+a {
+  foo = 6
+  bar = 3
+  baz {
+    qux = 4
+    quux = 12
+  }
+}
+b {
+  foo = 7
+  bar = 3
+  baz {
+    qux = 4
+    quux = 12
+  }
+}
+c {
+  qux = 4
+  quux = 12
+}
+d {
+  qux = 5
+  quux = 15
+}
+e = "Class `imported` cannot be extended or used as type because it amends another module or class."
+f = "Class `imported` cannot be extended or used as type because it amends another module or class."
+g = "Module `imported` cannot be extended or used as type because it amends another module or class."

pkl-core/src/test/files/LanguageSnippetTests/output/basic/import5.err

@@ -0,0 +1,6 @@
+–– Pkl Error ––
+Duplicate definition of member `_Widget`.
+
+x | class _Widget {}
+    ^^^^^^^^^^^^^
+at import5 (file:///$snippetsDir/input/basic/import5.pkl)

pkl-core/src/test/files/LanguageSnippetTests/output/basic/imported.pcf

@@ -1,2 +1,6 @@
 foo = 6
 bar = 3
+baz {
+  qux = 4
+  quux = 12
+}

pkl-core/src/test/files/LanguageSnippetTests/output/basic/imported2.pcf

@@ -0,0 +1,6 @@
+foo = 6
+bar = 3
+baz {
+  qux = 4
+  quux = 12
+}

pkl-core/src/test/files/LanguageSnippetTests/output/modules/amendModule7.pcf

@@ -0,0 +1,8 @@
+amendModuleClass {
+  qux = 5
+  quux = 15
+}
+amendModuleValue {
+  qux = 5
+  quux = 15
+}

pkl-core/src/test/files/LanguageSnippetTests/output/modules/amendModuleClass.err

@@ -0,0 +1,6 @@
+–– Pkl Error ––
+Cannot find property `output` in module `amendModuleClass`.
+
+Available properties in module `amendModuleClass`:
+quux
+qux

pkl-core/src/test/files/LanguageSnippetTests/output/modules/amendModuleValue.err

@@ -0,0 +1,6 @@
+–– Pkl Error ––
+Cannot find property `output` in module `amendModuleValue`.
+
+Available properties in module `amendModuleValue`:
+quux
+qux

pkl-core/src/test/files/LanguageSnippetTests/output/modules/extendModule2.pcf

@@ -0,0 +1,6 @@
+extendModuleClass {
+  qux = 2
+  quux = 6
+  corge = 12
+}
+extendModuleValue = "Class `imported#Widget` cannot be extended or used as type because it amends another module or class."