method refs: ambiguity (IDEA-113078)

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

@@ -693,7 +693,6 @@ public class LambdaUtil {
   }
 
   private static int isMoreSpecific(PsiType returnType, PsiType returnType1, PsiType lambdaType) {
-    if (returnType == PsiType.VOID || returnType1 == PsiType.VOID) return 0;
     TypeKind typeKind = TypeKind.PRIMITIVE;
     if (lambdaType instanceof PsiLambdaExpressionType) {
       typeKind = areLambdaReturnExpressionsPrimitive((PsiLambdaExpressionType)lambdaType);

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/methodRef/VoidReturnTypeAmbiguity.java

@@ -0,0 +1,29 @@
+class App {
+
+    public static void main(String[] args) {
+        test(App::getLength);
+    }
+
+    private static Integer getLength(String word) {
+        return word.length();
+    }
+
+
+    private static void <warning descr="Private method 'test(App.Consumer<java.lang.String>)' is never used">test</warning>(Consumer<String> consumer) {
+        consumer.accept("Hello World");
+    }
+
+    private static void test(Function<String, Integer> function) {
+        Integer result = function.apply("Hello World");
+        System.out.println(result);
+    }
+
+    interface Function<T, R> {
+        R apply(T t);
+    }
+
+    interface Consumer<T> {
+        void accept(T t);
+    }
+}
+

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

@@ -79,6 +79,7 @@ public class MethodRefHighlightingTest extends LightDaemonAnalyzerTestCase {
   public void testMethodRefAcceptance() { doTest(); }
   public void testVarargsMethodRef() { doTest(); }
   public void testExprReceiver() { doTest(); }
+  public void testVoidReturnTypeAmbiguity() { doTest(true); }
 
   public void testTypeParameterWithExtendsList() throws Exception {
     doTest();