8023389: Javac fails to infer type for lambda used with intersection type and wildcards

Reviewed-by: jjg, vromero
Contributed-by: maurizio.cimadamore@oracle.com

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

@@ -2319,30 +2319,37 @@ public class Attr extends JCTree.Visitor {
         boolean needsRecovery =
                 resultInfo.checkContext.deferredAttrContext().mode == DeferredAttr.AttrMode.CHECK;
         try {
-            Type target = pt();
+            Type currentTarget = pt();
             List<Type> explicitParamTypes = null;
             if (that.paramKind == JCLambda.ParameterKind.EXPLICIT) {
                 //attribute lambda parameters
                 attribStats(that.params, localEnv);
                 explicitParamTypes = TreeInfo.types(that.params);
-                target = infer.instantiateFunctionalInterface(that, target, explicitParamTypes, resultInfo.checkContext);
             }
 
             Type lambdaType;
             if (pt() != Type.recoveryType) {
-                target = targetChecker.visit(target, that);
-                lambdaType = types.findDescriptorType(target);
+                /* We need to adjust the target. If the target is an
+                 * intersection type, for example: SAM & I1 & I2 ...
+                 * the target will be updated to SAM
+                 */
+                currentTarget = targetChecker.visit(currentTarget, that);
+                if (explicitParamTypes != null) {
+                    currentTarget = infer.instantiateFunctionalInterface(that,
+                            currentTarget, explicitParamTypes, resultInfo.checkContext);
+                }
+                lambdaType = types.findDescriptorType(currentTarget);
             } else {
-                target = Type.recoveryType;
+                currentTarget = Type.recoveryType;
                 lambdaType = fallbackDescriptorType(that);
             }
 
-            setFunctionalInfo(localEnv, that, pt(), lambdaType, target, resultInfo.checkContext);
+            setFunctionalInfo(localEnv, that, pt(), lambdaType, currentTarget, resultInfo.checkContext);
 
             if (lambdaType.hasTag(FORALL)) {
                 //lambda expression target desc cannot be a generic method
                 resultInfo.checkContext.report(that, diags.fragment("invalid.generic.lambda.target",
-                        lambdaType, kindName(target.tsym), target.tsym));
+                        lambdaType, kindName(currentTarget.tsym), currentTarget.tsym));
                 result = that.type = types.createErrorType(pt());
                 return;
             }
@@ -2376,7 +2383,7 @@ public class Attr extends JCTree.Visitor {
 
                 if (arityMismatch) {
                     resultInfo.checkContext.report(that, diags.fragment("incompatible.arg.types.in.lambda"));
-                        result = that.type = types.createErrorType(target);
+                        result = that.type = types.createErrorType(currentTarget);
                         return;
                 }
             }
@@ -2403,7 +2410,7 @@ public class Attr extends JCTree.Visitor {
                 attribStats(body.stats, localEnv);
             }
 
-            result = check(that, target, VAL, resultInfo);
+            result = check(that, currentTarget, VAL, resultInfo);
 
             boolean isSpeculativeRound =
                     resultInfo.checkContext.deferredAttrContext().mode == DeferredAttr.AttrMode.SPECULATIVE;
@@ -2414,9 +2421,9 @@ public class Attr extends JCTree.Visitor {
             checkLambdaCompatible(that, lambdaType, resultInfo.checkContext, isSpeculativeRound);
 
             if (!isSpeculativeRound) {
-                checkAccessibleTypes(that, localEnv, resultInfo.checkContext.inferenceContext(), lambdaType, target);
+                checkAccessibleTypes(that, localEnv, resultInfo.checkContext.inferenceContext(), lambdaType, currentTarget);
             }
-            result = check(that, target, VAL, resultInfo);
+            result = check(that, currentTarget, VAL, resultInfo);
         } catch (Types.FunctionDescriptorLookupError ex) {
             JCDiagnostic cause = ex.getDiagnostic();
             resultInfo.checkContext.report(that, cause);

test/tools/javac/lambda/8023389/T8023389.java

+/*
+ * Copyright (c) 2013, 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 8023389
+ * @summary Javac fails to infer type for lambda used with intersection type and wildcards
+ * @compile T8023389.java
+ */
+public class T8023389 {
+
+    static class U1 {}
+    static class X1 extends U1 {}
+
+    interface I { }
+
+    interface SAM<T> {
+        void m(T t);
+    }
+
+    /* Strictly speaking only the second of the following declarations provokes the bug.
+     * But the first line is also a useful test case.
+     */
+    SAM<? extends U1> sam1 = (SAM<? extends U1>) (X1 x) -> { };
+    SAM<? extends U1> sam2 = (SAM<? extends U1> & I) (X1 x) -> { };
+}