8254571: Erroneous generic type inference in a lambda expression with a checked exception

Reviewed-by: jlahoda, mcimadamore

Author: Vicente Romero

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

@@ -1217,6 +1217,7 @@ public void visitLambda(JCLambda tree) {
                     freeArgVars.nonEmpty()) {
                 stuckVars.addAll(freeArgVars);
                 depVars.addAll(inferenceContext.freeVarsIn(descType.getReturnType()));
+                depVars.addAll(inferenceContext.freeVarsIn(descType.getThrownTypes()));
             }
             scanLambdaBody(tree, descType.getReturnType());
         }
@@ -1238,6 +1239,7 @@ public void visitReference(JCMemberReference tree) {
                     tree.getOverloadKind() != JCMemberReference.OverloadKind.UNOVERLOADED) {
                 stuckVars.addAll(freeArgVars);
                 depVars.addAll(inferenceContext.freeVarsIn(descType.getReturnType()));
+                depVars.addAll(inferenceContext.freeVarsIn(descType.getThrownTypes()));
             }
         }
 

test/langtools/tools/javac/lambda/considerExceptionTVarInStuckExprs/ConsiderExceptionTVarsInStuckExprs.java

@@ -0,0 +1,50 @@
+/*
+ * 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 8254571
+ * @summary Erroneous generic type inference in a lambda expression with a checked exception
+ * @compile ConsiderExceptionTVarsInStuckExprs.java
+ */
+
+class ConsiderExceptionTVarsInStuckExprs {
+
+    public static void test() {
+        outer(nested(x -> mightThrow()));
+        outer(nested(ConsiderExceptionTVarsInStuckExprs::mightThrow2));
+    }
+
+    static <A> void outer(Object o) {}
+
+    static <B, C, E extends Throwable> B nested(Fun<C,E> fun) {
+        return null;
+    }
+
+    interface Fun<X, Y extends Throwable> {
+        void m(X t) throws Y;
+    }
+
+    static void mightThrow() throws Exception {}
+    static <C> void mightThrow2(C c) throws Exception {}
+}