8262117: jextract crashes with javac compilation error "class u is al…

…ready defined"

src/jdk.incubator.jextract/share/classes/jdk/internal/jextract/impl/JavaSourceBuilder.java

@@ -205,7 +205,14 @@ String build() {
      */
     final String uniqueNestedClassName(String name) {
         name = Utils.javaSafeIdentifier(name);
-        return nestedClassNames.add(name.toLowerCase()) ? name : (name + "$" + nestedClassNameCount++);
+        var notSeen = nestedClassNames.add(name.toLowerCase());
+        var notEnclosed = !isEnclosedBySameName(name.toLowerCase());
+        return notSeen && notEnclosed? name : (name + "$" + nestedClassNameCount++);
+    }
+
+    // is the name enclosed enclosed by a class of the same name?
+    boolean isEnclosedBySameName(String name) {
+        return false;
     }
 
     protected void emitPackagePrefix() {

src/jdk.incubator.jextract/share/classes/jdk/internal/jextract/impl/NestedClassBuilder.java

@@ -45,6 +45,11 @@ protected String mods() {
                 "public " : "public static ";
     }
 
+    @Override
+    boolean isEnclosedBySameName(String name) {
+        return className().equals(name) || enclosing.isEnclosedBySameName(name);
+    }
+
     @Override
     String fullName() {
         return enclosing.className() + "." + className();

test/jdk/tools/jextract/Test8262117.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2021, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.lang.reflect.Method;
+import java.nio.file.Path;
+import jdk.incubator.foreign.NativeScope;
+import org.testng.annotations.Test;
+import static org.testng.Assert.assertNull;
+import static org.testng.Assert.assertNotNull;
+import static org.testng.Assert.assertTrue;
+
+/*
+ * @test
+ * @modules jdk.incubator.jextract
+ * @library /test/lib
+ * @build JextractToolRunner
+ * @bug 8262117
+ * @summary jextract crashes with javac compilation error "class u is already defined"
+ * @run testng/othervm -Dforeign.restricted=permit Test8262117
+ */
+public class Test8262117 extends JextractToolRunner {
+    @Test
+    public void testNameClash() {
+        Path test8262117Output = getOutputFilePath("test8262117_gen");
+        Path test8262117H = getInputFilePath("test8262117.h");
+        run("-d", test8262117Output.toString(), test8262117H.toString()).checkSuccess();
+        try(Loader loader = classLoader(test8262117Output)) {
+            Class<?> cls = loader.loadClass("test8262117_h");
+            assertNotNull(cls);
+
+            assertNotNull(loader.loadClass("test8262117_h$u"));
+            assertNotNull(loader.loadClass("test8262117_h$u$outer$u$0"));
+            assertNotNull(loader.loadClass("test8262117_h$v"));
+            assertNotNull(loader.loadClass("test8262117_h$v$v$0"));
+        } finally {
+            deleteDir(test8262117Output);
+        }
+    }
+}

test/jdk/tools/jextract/test8262117.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2021, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+
+union {
+   struct {
+      union {
+         struct { int x; } inner;
+      } u;
+   } outer;
+} u;
+
+
+union {
+    union {
+       int x; long y;
+    } v;
+} v;