new inference: stop collecting constraints if target type is proper (IDEA-136412)

java/java-psi-impl/src/com/intellij/psi/impl/source/resolve/graphInference/InferenceSession.java

@@ -308,7 +308,7 @@ public class InferenceSession {
           if (calledMethod != null && PsiPolyExpressionUtil.isMethodCallPolyExpression(arg, calledMethod)) {
             collectAdditionalConstraints(additionalConstraints, (PsiCallExpression)arg);
           }
-        } else if (arg instanceof PsiLambdaExpression) {
+        } else if (arg instanceof PsiLambdaExpression && !isProperType(retrieveNonPrimitiveEqualsBounds(myInferenceVariables).substitute(parameterType))) {
           collectLambdaReturnExpression(additionalConstraints, (PsiLambdaExpression)arg, parameterType);
         }
       }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/additionalConstraints/StopCollectingAdditionalConstraintsWhenLambdaReturnTypeIsProper.java

@@ -0,0 +1,15 @@
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+class Test {
+  private List<Map<String, String>> foo(Stream<Map.Entry<String, List<String>>> stream) {
+    return then(v -> stream.collect(Collectors.toMap(Map.Entry::getKey, e -> e.getValue().toString())));
+  }
+
+  private <V> List<V> then(Function<Void, V> f) {
+    return null;
+  }
+}

java/java-tests/testSrc/com/intellij/codeInsight/daemon/lambda/NewInferenceCollectingAdditionalConstraintsTest.java

@@ -28,6 +28,10 @@ public class NewInferenceCollectingAdditionalConstraintsTest extends LightDaemon
     doTest();
   }
 
+  public void testStopCollectingAdditionalConstraintsWhenLambdaReturnTypeIsProper() throws Exception {
+    doTest();
+  }
+
   private void doTest() {
     doTest(true);
   }