functional type erasure: check if resulted type functional (IDEA-142341)

java/java-psi-api/src/com/intellij/psi/PsiTypeVisitor.java

@@ -78,14 +78,14 @@ public class PsiTypeVisitor<A> {
   public A visitLambdaExpressionType(PsiLambdaExpressionType lambdaExpressionType) {
     final PsiLambdaExpression lambdaExpression = lambdaExpressionType.getExpression();
     final PsiType interfaceType = lambdaExpression.getFunctionalInterfaceType();
-    if (interfaceType != null) return interfaceType.accept(this);
+    if (interfaceType != null && LambdaUtil.isFunctionalType(interfaceType)) return interfaceType.accept(this);
     return visitType(lambdaExpressionType);
   }
   
   public A visitMethodReferenceType(PsiMethodReferenceType methodReferenceType) {
     final PsiMethodReferenceExpression expression = methodReferenceType.getExpression();
     final PsiType interfaceType = expression.getFunctionalInterfaceType();
-    if (interfaceType != null) return interfaceType.accept(this);
+    if (interfaceType != null && LambdaUtil.isFunctionalType(interfaceType)) return interfaceType.accept(this);
     return visitType(methodReferenceType);
   }
 }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/overloadResolution/FunctionalExpressionTypeErasure.java

@@ -0,0 +1,39 @@
+interface Functional {
+  void a(String s);
+}
+
+interface NonFunctional {
+  void b(String s);
+  void c();
+}
+
+interface P<<warning descr="Type parameter 'T' is never used">T</warning>> {
+  void subscribe(Functional f);
+  void subscribe(NonFunctional nf);
+}
+
+class Test {
+  void foo(P p) {
+    p.subscribe(s -> {});
+  }
+}
+
+interface FunctionalExact {
+  void a();
+}
+
+interface NonFunctionalExact {
+  void b();
+  void c();
+}
+
+interface PExact<<warning descr="Type parameter 'T' is never used">T</warning>> {
+  void subscribe(FunctionalExact f);
+  void subscribe(NonFunctionalExact nf);
+}
+
+class TestExact {
+  void foo(PExact p) {
+    p.subscribe(() -> {});
+  }
+}

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

@@ -130,6 +130,10 @@ public class OverloadResolutionTest extends LightDaemonAnalyzerTestCase {
     doTest();
   }
 
+  public void testFunctionalExpressionTypeErasure() throws Exception {
+    doTest();
+  }
+
   private void doTest() {
     doTest(true);
   }