lambda/diamond inference: accept wildcards in lambda return types (IDEA-108955)

java/java-psi-impl/src/com/intellij/psi/impl/source/resolve/PsiResolveHelperImpl.java

@@ -1048,6 +1048,7 @@ public class PsiResolveHelperImpl implements PsiResolveHelper {
         if (expectedType == null) {
           return null;
         }
+        expectedType = GenericsUtil.eliminateWildcards(expectedType);
       } else if (parent instanceof PsiConditionalExpression) {
         if (PsiUtil.isLanguageLevel8OrHigher(parent)) {
           try {

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/highlighting/DiamondInference.java

@@ -0,0 +1,14 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+class Demo {
+    public static void main(String[] args) {
+        Function<? super String, ? extends List<String>> mappingFunction = key -> new ArrayList<>();
+    }
+
+    interface Function<T, R> {
+      public R apply(T t);
+    }
+}

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

@@ -88,6 +88,7 @@ public class LambdaHighlightingTest extends LightDaemonAnalyzerTestCase {
   public void testDeclaredTypeParameterBoundsAndUnboundedWildcard() { doTest(); }
   public void testConflictResolution() throws Exception {doTest();}
   public void testIDEA108195() throws Exception {doTest();}
+  public void testDiamondInference() throws Exception { doTest();}
 
   private void doTest() {
     doTest(false);