8328481: Implement JEP 476: Module Import Declarations (Preview)

Co-authored-by: Jim Laskey <jlaskey@openjdk.org>
Reviewed-by: mcimadamore, vromero

src/java.base/share/classes/jdk/internal/javac/PreviewFeature.java

@@ -81,6 +81,8 @@ public enum Feature {
         CLASSFILE_API,
         @JEP(number=473, title="Stream Gatherers", status="Second Preview")
         STREAM_GATHERERS,
+        @JEP(number=476, title="Module Import Declarations", status="Preview")
+        MODULE_IMPORTS,
         LANGUAGE_MODEL,
         /**
          * A key for testing.

src/jdk.compiler/share/classes/com/sun/source/tree/ImportTree.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,6 +25,8 @@
 
 package com.sun.source.tree;
 
+import jdk.internal.javac.PreviewFeature;
+
 /**
  * A tree node for an import declaration.
  *
@@ -47,6 +49,12 @@ public interface ImportTree extends Tree {
      * @return true if this is a static import
      */
     boolean isStatic();
+    /**
+     * {@return true if this is an module import declaration.}
+     * @since 23
+     */
+    @PreviewFeature(feature=PreviewFeature.Feature.MODULE_IMPORTS, reflective=true)
+    boolean isModule();
 
     /**
      * Returns the qualified identifier for the declaration(s)

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Preview.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -210,6 +210,7 @@ public boolean isPreview(Feature feature) {
             case IMPLICIT_CLASSES -> true;
             case SUPER_INIT -> true;
             case PRIMITIVE_PATTERNS -> true;
+            case MODULE_IMPORTS -> true;
             //Note: this is a backdoor which allows to optionally treat all features as 'preview' (for testing).
             //When real preview features will be added, this method can be implemented to return 'true'
             //for those selected features, and 'false' for all the others.

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Source.java

@@ -255,6 +255,7 @@ public enum Feature {
         UNNAMED_VARIABLES(JDK22, Fragments.FeatureUnnamedVariables, DiagKind.PLURAL),
         PRIMITIVE_PATTERNS(JDK23, Fragments.FeaturePrimitivePatterns, DiagKind.PLURAL),
         SUPER_INIT(JDK22, Fragments.FeatureSuperInit, DiagKind.NORMAL),
+        MODULE_IMPORTS(JDK23, Fragments.FeatureModuleImports, DiagKind.PLURAL),
         ;
 
         enum DiagKind {

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Check.java

@@ -4396,7 +4396,9 @@ public void checkFunctionalInterface(JCClassDecl tree, ClassSymbol cs) {
     }
 
     public void checkImportsResolvable(final JCCompilationUnit toplevel) {
-        for (final JCImport imp : toplevel.getImports()) {
+        for (final JCImportBase impBase : toplevel.getImports()) {
+            if (!(impBase instanceof JCImport imp))
+                continue;
             if (!imp.staticImport || !imp.qualid.hasTag(SELECT))
                 continue;
             final JCFieldAccess select = imp.qualid;
@@ -4420,8 +4422,9 @@ public void checkImportsResolvable(final JCCompilationUnit toplevel) {
 
     // Check that packages imported are in scope (JLS 7.4.3, 6.3, 6.5.3.1, 6.5.3.2)
     public void checkImportedPackagesObservable(final JCCompilationUnit toplevel) {
-        OUTER: for (JCImport imp : toplevel.getImports()) {
-            if (!imp.staticImport && TreeInfo.name(imp.qualid) == names.asterisk) {
+        OUTER: for (JCImportBase impBase : toplevel.getImports()) {
+            if (impBase instanceof JCImport imp && !imp.staticImport &&
+                TreeInfo.name(imp.qualid) == names.asterisk) {
                 TypeSymbol tsym = imp.qualid.selected.type.tsym;
                 if (tsym.kind == PCK && tsym.members().isEmpty() &&
                     !(Feature.IMPORT_ON_DEMAND_OBSERVABLE_PACKAGES.allowedInSource(source) && tsym.exists())) {

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/TreeDiffer.java

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2018, Google LLC. All rights reserved.
- * Copyright (c) 2018, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -67,6 +67,7 @@
 import com.sun.tools.javac.tree.JCTree.JCMethodInvocation;
 import com.sun.tools.javac.tree.JCTree.JCModifiers;
 import com.sun.tools.javac.tree.JCTree.JCModuleDecl;
+import com.sun.tools.javac.tree.JCTree.JCModuleImport;
 import com.sun.tools.javac.tree.JCTree.JCNewArray;
 import com.sun.tools.javac.tree.JCTree.JCNewClass;
 import com.sun.tools.javac.tree.JCTree.JCOpens;
@@ -410,6 +411,12 @@ public void visitImport(JCImport tree) {
         result = tree.staticImport == that.staticImport && scan(tree.qualid, that.qualid);
     }
 
+    @Override
+    public void visitModuleImport(JCModuleImport tree) {
+        JCModuleImport that = (JCModuleImport) parameter;
+        result = scan(tree.module, that.module);
+    }
+
     @Override
     public void visitIndexed(JCArrayAccess tree) {
         JCArrayAccess that = (JCArrayAccess) parameter;

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/TypeEnter.java

@@ -32,16 +32,15 @@
 import javax.tools.JavaFileObject;
 
 import com.sun.tools.javac.code.*;
+import com.sun.tools.javac.code.Directive.ExportsDirective;
+import com.sun.tools.javac.code.Directive.RequiresDirective;
 import com.sun.tools.javac.code.Lint.LintCategory;
 import com.sun.tools.javac.code.Scope.ImportFilter;
-import com.sun.tools.javac.code.Scope.ImportScope;
 import com.sun.tools.javac.code.Scope.NamedImportScope;
 import com.sun.tools.javac.code.Scope.StarImportScope;
 import com.sun.tools.javac.code.Scope.WriteableScope;
 import com.sun.tools.javac.code.Source.Feature;
 import com.sun.tools.javac.comp.Annotate.AnnotationTypeMetadata;
-import com.sun.tools.javac.parser.Parser;
-import com.sun.tools.javac.parser.ParserFactory;
 import com.sun.tools.javac.tree.*;
 import com.sun.tools.javac.util.*;
 import com.sun.tools.javac.util.DefinedBy.Api;
@@ -57,7 +56,6 @@
 import static com.sun.tools.javac.code.Kinds.Kind.*;
 import static com.sun.tools.javac.code.TypeTag.CLASS;
 import static com.sun.tools.javac.code.TypeTag.ERROR;
-import com.sun.tools.javac.resources.CompilerProperties.Fragments;
 
 import static com.sun.tools.javac.code.TypeTag.*;
 import static com.sun.tools.javac.tree.JCTree.Tag.*;
@@ -114,8 +112,6 @@ public class TypeEnter implements Completer {
     private final Lint lint;
     private final TypeEnvs typeEnvs;
     private final Dependencies dependencies;
-    private final ParserFactory parserFactory;
-    private final Preview preview;
 
     public static TypeEnter instance(Context context) {
         TypeEnter instance = context.get(typeEnterKey);
@@ -143,8 +139,6 @@ protected TypeEnter(Context context) {
         lint = Lint.instance(context);
         typeEnvs = TypeEnvs.instance(context);
         dependencies = Dependencies.instance(context);
-        parserFactory = ParserFactory.instance(context);
-        preview = Preview.instance(context);
         Source source = Source.instance(context);
         allowDeprecationOnImport = Feature.DEPRECATION_ON_IMPORT.allowedInSource(source);
     }
@@ -370,9 +364,7 @@ private void resolveImports(JCCompilationUnit tree, Env<AttrContext> env) {
                 if (tree.getPackage() != null && decl == null)
                     checkClassPackageClash(tree.getPackage());
 
-                for (JCImport imp : tree.getImports()) {
-                    doImport(imp);
-                }
+                handleImports(tree.getImports());
 
                 if (decl != null) {
                     DiagnosticPosition prevCheckDeprecatedLintPos = deferredLintHandler.setPos(decl.pos());
@@ -394,6 +386,16 @@ private void resolveImports(JCCompilationUnit tree, Env<AttrContext> env) {
             }
         }
 
+        private void handleImports(List<JCImportBase> imports) {
+            for (JCImportBase imp : imports) {
+                if (imp instanceof JCModuleImport mimp) {
+                    doModuleImport(mimp);
+                } else {
+                    doImport((JCImport) imp);
+                }
+            }
+        }
+
         private void checkClassPackageClash(JCPackageDecl tree) {
             // check that no class exists with same fully qualified name as
             // toplevel package
@@ -445,6 +447,57 @@ private void doImport(JCImport tree) {
             }
         }
 
+        private void doModuleImport(JCModuleImport tree) {
+            Name moduleName = TreeInfo.fullName(tree.module);
+            ModuleSymbol module = syms.getModule(moduleName);
+
+            if (module != null) {
+                if (!env.toplevel.modle.readModules.contains(module)) {
+                    if (env.toplevel.modle.isUnnamed()) {
+                        log.error(tree.pos, Errors.ImportModuleDoesNotReadUnnamed(module));
+                    } else {
+                        log.error(tree.pos, Errors.ImportModuleDoesNotRead(env.toplevel.modle,
+                                                                           module));
+                    }
+                    //error recovery, make sure the module is completed:
+                    module.getDirectives();
+                }
+
+                List<ModuleSymbol> todo = List.of(module);
+                Set<ModuleSymbol> seenModules = new HashSet<>();
+
+                while (!todo.isEmpty()) {
+                    ModuleSymbol currentModule = todo.head;
+
+                    todo = todo.tail;
+
+                    if (!seenModules.add(currentModule)) {
+                        continue;
+                    }
+
+                    for (ExportsDirective export : currentModule.exports) {
+                        if (export.modules != null && !export.modules.contains(env.toplevel.packge.modle)) {
+                            continue;
+                        }
+
+                        PackageSymbol pkg = export.getPackage();
+                        JCImport nestedImport = make.at(tree.pos)
+                                .Import(make.Select(make.QualIdent(pkg), names.asterisk), false);
+
+                        doImport(nestedImport);
+                    }
+
+                    for (RequiresDirective requires : currentModule.requires) {
+                        if (requires.isTransitive()) {
+                            todo = todo.prepend(requires.module);
+                        }
+                    }
+                }
+            } else {
+                log.error(tree.pos, Errors.ImportModuleNotFound(moduleName));
+            }
+        }
+
         Type attribImportType(JCTree tree, Env<AttrContext> env) {
             Assert.check(completionEnabled);
             Lint prevLint = chk.setLint(allowDeprecationOnImport ?

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavacParser.java

@@ -4252,6 +4252,13 @@ protected JCTree importDeclaration() {
         if (token.kind == STATIC) {
             importStatic = true;
             nextToken();
+        } else if (token.kind == IDENTIFIER && token.name() == names.module &&
+                   peekToken(TokenKind.IDENTIFIER)) {
+            checkSourceLevel(Feature.MODULE_IMPORTS);
+            nextToken();
+            JCExpression moduleName = qualident(false);
+            accept(SEMI);
+            return toP(F.at(pos).ModuleImport(moduleName));
         }
         JCExpression pid = toP(F.at(token.pos).Ident(ident()));
         do {

src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties

@@ -3218,6 +3218,9 @@ compiler.misc.feature.implicit.classes=\
 compiler.misc.feature.super.init=\
     statements before super()
 
+compiler.misc.feature.module.imports=\
+    module imports
+
 compiler.warn.underscore.as.identifier=\
     as of release 9, ''_'' is a keyword, and may not be used as an identifier
 
@@ -3528,6 +3531,18 @@ compiler.err.module.not.found=\
 compiler.warn.module.not.found=\
     module not found: {0}
 
+# 0: name
+compiler.err.import.module.not.found=\
+    imported module not found: {0}
+
+# 0: symbol
+compiler.err.import.module.does.not.read.unnamed=\
+    unnamed module does not read: {0}
+
+# 0: symbol, 1: symbol
+compiler.err.import.module.does.not.read=\
+    module {0} does not read: {1}
+
 compiler.err.too.many.modules=\
     too many module declarations found