exact method refs most specific: void compatibility

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

@@ -1106,15 +1106,15 @@ public class InferenceSession {
         return false;
       }
 
-      final boolean sPrimitive = sReturnType instanceof PsiPrimitiveType;
-      final boolean tPrimitive = tReturnType instanceof PsiPrimitiveType;
+      final boolean sPrimitive = sReturnType instanceof PsiPrimitiveType && sReturnType != PsiType.VOID;
+      final boolean tPrimitive = tReturnType instanceof PsiPrimitiveType && tReturnType != PsiType.VOID;
 
       if (sPrimitive ^ tPrimitive) {
         final PsiMember member = ((PsiMethodReferenceExpression)arg).getPotentiallyApplicableMember();
         LOG.assertTrue(member != null);
         if (member instanceof PsiMethod) {
           final PsiType methodReturnType = ((PsiMethod)member).getReturnType();
-          if (sPrimitive && methodReturnType instanceof PsiPrimitiveType ||
+          if (sPrimitive && methodReturnType instanceof PsiPrimitiveType && methodReturnType != PsiType.VOID ||
               tPrimitive && methodReturnType instanceof PsiClassType) {
             return true;
           }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/mostSpecific/VoidConflict.java

@@ -0,0 +1,46 @@
+class Test {
+
+  interface I { void i_bar(); }
+  interface I1<T> { T i1_bar(); }
+
+  private void m(I i) {System.out.println(i);}
+  private void <warning descr="Private method 'm(Test.I1<java.lang.String>)' is never used">m</warning>(I1<String> i1) {System.out.println(i1);}
+
+  void test() {
+    m(Test::foo);
+  }
+
+  public static int foo() {
+    return 0;
+  }
+}
+
+class Test1 {
+
+  interface I { void i_bar(); }
+  interface I1<T> { T i1_bar(); }
+
+  void m(I i) { System.out.println(i);}
+  void m(I1<String> i1) { System.out.println(i1);}
+
+  void test() {
+    m(Test1::foo);
+  }
+
+  public static String foo() {return "";}
+}
+
+class Test2 {
+
+  interface I { void i_bar(); }
+  interface I1<T> { T i1_bar(); }
+
+  void m(I i) { System.out.println(i);}
+  void m(I1<String> i1) { System.out.println(i1);}
+
+  void test() {
+    m(Test2::foo);
+  }
+
+  public static void foo() {}
+}

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

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2000-2014 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.codeInsight.daemon.lambda;
+
+import com.intellij.codeInsight.daemon.LightDaemonAnalyzerTestCase;
+import com.intellij.codeInspection.LocalInspectionTool;
+import com.intellij.codeInspection.unusedSymbol.UnusedSymbolLocalInspection;
+import com.intellij.openapi.projectRoots.JavaSdkVersion;
+import com.intellij.openapi.projectRoots.Sdk;
+import com.intellij.testFramework.IdeaTestUtil;
+import org.jetbrains.annotations.NonNls;
+import org.jetbrains.annotations.NotNull;
+
+public class MostSpecificResolutionTest extends LightDaemonAnalyzerTestCase {
+  @NonNls static final String BASE_PATH = "/codeInsight/daemonCodeAnalyzer/lambda/mostSpecific";
+
+  @NotNull
+  @Override
+  protected LocalInspectionTool[] configureLocalInspectionTools() {
+    return new LocalInspectionTool[]{
+      new UnusedSymbolLocalInspection(),
+    };
+  }
+
+  public void testVoidConflict() throws Exception {
+    doTest();
+  }
+
+  private void doTest() {
+    doTest(true);
+  }
+
+  private void doTest(boolean warnings) {
+    IdeaTestUtil.setTestVersion(JavaSdkVersion.JDK_1_8, getModule(), getTestRootDisposable());
+    doTestNewInference(BASE_PATH + "/" + getTestName(false) + ".java", warnings, false);
+  }
+
+  @Override
+  protected Sdk getProjectJDK() {
+    return IdeaTestUtil.getMockJdk18();
+  }
+}