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

+ resilience: avoid accepting a sourceType being completed already
+ reduce fix for 544306 to modular projects

Fixes eclipse-jdt#3273

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/Compiler.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
@@ -335,6 +335,14 @@ public void accept(IBinaryType binaryType, PackageBinding packageBinding, Access
 	 */
 	@Override
 	public void accept(ICompilationUnit sourceUnit, AccessRestriction accessRestriction) {
+		if (this.lookupEnvironment.unitBeingCompleted != null) {
+			// resilience for https://github.com/eclipse-jdt/eclipse.jdt.core/issues/3273
+			// NEVER accept a sourceUnit that is already being completed
+			char[] fileName1 = this.lookupEnvironment.unitBeingCompleted.compilationResult.fileName;
+			char[] fileName2 = sourceUnit.getFileName();
+			if (CharOperation.equals(fileName1, fileName2) && !CharOperation.equals(fileName1, TypeConstants.MODULE_INFO_FILE_NAME))
+				return;
+		}
 		// Switch the current policy and compilation result for this unit to the requested one.
 		CompilationResult unitResult =
 			new CompilationResult(sourceUnit, this.totalUnits, this.totalUnits, this.options.maxProblemsPerUnit);

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

@@ -1573,17 +1573,23 @@ enum Kind { Good, Bad }
 					"""
 					package common.test;
 					import static common.pack1.C1.*; // this import pulls in classes from the other project
+					import common.pack1.C1;
 					public class Client {
 						String s = CONST1;
+						C1<?> c1;
 					}
 					""");
 
 			IJavaElement[] types = { project2.findType("common.test.Client") };
 			ASTParser astParser = ASTParser.newParser(AST.getJLSLatest());
 			astParser.setProject(project2);
 			IBinding[] bindings = astParser.createBindings(types, null);
-			System.out.println(bindings);
-			// TODO add useful assertions once we reach here
+			assertEquals(1, bindings.length);
+			ITypeBinding type = (ITypeBinding) bindings[0];
+			IVariableBinding c1 = type.getDeclaredFields()[0];
+			IModuleBinding module = c1.getType().getModule();
+			assertNotNull(module);
+			assertEquals("first", 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, 2020 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
@@ -3741,6 +3741,14 @@ 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, 2021 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
@@ -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())) {
+		if (!Objects.equals(project, root.getJavaProject()) && project.isModular()) {
 			IClasspathEntry classpathEntry2 = rootToEntry.apply(root);
 			if (classpathEntry2 instanceof ClasspathEntry) {
 				if (!((ClasspathEntry) classpathEntry2).isModular()) {