8273234: extended 'for' with expression of type tvar causes the compiler to crash

Reviewed-by: jlahoda

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

@@ -1546,7 +1546,7 @@ public class Attr extends JCTree.Visitor {
                     // Check the return type of the method iterator().
                     // This is the bare minimum we need to verify to make sure code generation doesn't crash.
                     Symbol iterSymbol = rs.resolveInternalMethod(tree.pos(),
-                            loopEnv, exprType, names.iterator, List.nil(), List.nil());
+                            loopEnv, types.skipTypeVars(exprType, false), names.iterator, List.nil(), List.nil());
                     if (types.asSuper(iterSymbol.type.getReturnType(), syms.iteratorType.tsym) == null) {
                         log.error(tree.pos(),
                                 Errors.ForeachNotApplicableToType(exprType, Fragments.TypeReqArrayOrIterable));

test/langtools/tools/javac/foreach/ExprTypeIsTypeVariableTest.java

@@ -0,0 +1,49 @@
+/*
+ * 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.
+ */
+
+/*
+ * @test
+ * @bug 8273234
+ * @summary extended 'for' with expression of type tvar causes the compiler to crash
+ * @compile ExprTypeIsTypeVariableTest.java
+ */
+
+import java.util.*;
+
+class ExprTypeIsTypeVariableTest {
+    abstract class A {}
+
+    abstract class ACD<E> implements Iterable<E> {
+        public Iterator<E> iterator() {
+            return null;
+        }
+    }
+
+    abstract class ALD<E> extends ACD<E> implements List<E> {}
+
+    abstract class ASP<NT extends A> extends ALD<A> {
+        <P extends ASP<NT>> void foo(P prod) {
+            for (A sym : prod) {}
+        }
+    }
+}