java.lang.StackOverflowError during "Requesting Java AST from selection"

change of strategy:
+ better hiding of modules seen via the classpath

Fixes eclipse-jdt#3273

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/env/ICompilationUnit.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2017 IBM Corporation and others.
+ * Copyright (c) 2000, 2024 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -61,7 +61,11 @@ default boolean ignoreOptionalProblems() {
  * @return the binding representing the module.
  */
 default ModuleBinding module(LookupEnvironment environment) {
-	return environment.getModule(getModuleName());
+	if (environment.nameEnvironment instanceof IModuleAwareNameEnvironment modEnv) {
+		char[] moduleName = modEnv.isOnModulePath(this) ? getModuleName() : ModuleBinding.UNNAMED;
+		return environment.getModule(moduleName);
+	}
+	return null;
 }
 /**
  * Returns the name of the module to which this compilation unit is associated.

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/env/IModuleAwareNameEnvironment.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2016, 2017 IBM Corporation and others.
+ * Copyright (c) 2016, 2024 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -132,6 +132,16 @@ default char[][] getUniqueModulesDeclaringPackage(char[][] packageName, char[] m
 	IModule getModule(char[] moduleName);
 	char[][] getAllAutomaticModules();
 
+	/**
+	 * If this environment focusses on one IJavaProject answer if the given
+	 * compilation unit is found on the module path, rather than the class path.
+	 * @param unit compilation unit to test
+	 * @return true iff unit is on the module path.
+	 */
+	default boolean isOnModulePath(ICompilationUnit unit) {
+		return true; // TODO: should more / all implementors implement this method?
+	}
+
 	/**
 	 * Ask the name environment to perform any updates (add-exports or add-reads) to the given module.
 	 * @param module the compiler representation of the module to updates

org.eclipse.jdt.core.tests.model/src/org/eclipse/jdt/core/tests/dom/ASTConverter9Test.java

@@ -1589,7 +1589,7 @@ public class Client {
 			IVariableBinding c1 = type.getDeclaredFields()[0];
 			IModuleBinding module = c1.getType().getModule();
 			assertNotNull(module);
-			assertEquals("first", module.getName());
+			assertEquals("", module.getName());
 		} finally {
 			deleteProject("P0");
 			deleteProject("P1");

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/JavaProject.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2024 IBM Corporation and others.
+ * Copyright (c) 2000, 2020 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -3741,14 +3741,6 @@ public IModuleDescription getModuleDescription() throws JavaModelException {
 		return null;
 	}
 
-	public boolean isModular() {
-		try {
-			return getModuleDescription() != null;
-		} catch (JavaModelException e) {
-			return false;
-		}
-	}
-
 	@Override
 	public IModuleDescription getOwnModuleDescription() throws JavaModelException {
 		JavaProjectElementInfo info = (JavaProjectElementInfo) getElementInfo();

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/NameLookup.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2024 IBM Corporation and others.
+ * Copyright (c) 2000, 2021 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -904,7 +904,7 @@ static IModuleDescription getModuleDescription(JavaProject project, IPackageFrag
 		IModuleDescription module = cache.get(root);
 		if (module != null)
 			return module != NO_MODULE ? module : null;
-		if (!Objects.equals(project, root.getJavaProject()) && project.isModular()) {
+		if (!Objects.equals(project, root.getJavaProject())) {
 			IClasspathEntry classpathEntry2 = rootToEntry.apply(root);
 			if (classpathEntry2 instanceof ClasspathEntry) {
 				if (!((ClasspathEntry) classpathEntry2).isModular()) {

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/SearchableEnvironment.java

@@ -22,6 +22,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import org.eclipse.core.resources.IProject;
 import org.eclipse.core.resources.IResource;
@@ -301,6 +302,22 @@ public void findModules(char[] prefix, ISearchRequestor requestor, IJavaProject
 		this.nameLookup.seekModule(prefix, true, new SearchableEnvironmentRequestor(requestor));
 	}
 
+	@Override
+	public boolean isOnModulePath(ICompilationUnit unit) {
+		if (unit instanceof CompilationUnit cUnit) {
+			IPackageFragmentRoot root = cUnit.originalFromClone().getPackageFragmentRoot();
+			if (Objects.equals(root.getJavaProject(), this.project))
+				return true; // current project: modular if it contains module-info :)
+			IClasspathEntry entry = this.nameLookup.rootToResolvedEntries.get(root);
+			if (entry instanceof ClasspathEntry cpEntry)
+				return cpEntry.isModular();
+			return true; // out-of-band resolution / transitive dependency?
+		} else if (unit instanceof BasicCompilationUnit bUnit) {
+			return bUnit.moduleName != null;
+		}
+		return false;
+	}
+
 	/**
 	 * Find the packages that start with the given prefix.
 	 * A valid prefix is a qualified name separated by periods