lambda: void compatibility guess

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

@@ -40,7 +40,7 @@ public class LambdaHighlightingUtil {
       final PsiElement body = lambdaExpression.getBody();
       if (body instanceof PsiCodeBlock) {
         if (!LambdaUtil.getReturnExpressions(lambdaExpression).isEmpty()) return "Unexpected return value";
-      } else if (body instanceof PsiExpression) {
+      } else if (body instanceof PsiReferenceExpression || body instanceof PsiLiteralExpression) {
         final PsiType type = ((PsiExpression)body).getType();
         if (type != PsiType.VOID) {
           return "Incompatible return type " + (type == PsiType.NULL || type == null ? "<null>" : type.getPresentableText()) +" in lambda expression";

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

@@ -0,0 +1,12 @@
+public class Main {
+    interface I<T> {
+        void m(T t);
+    }
+
+    {
+        String s = "";
+        I<Object> arr1 = <error descr="Incompatible return type String in lambda expression">(t) -> s</error>;
+        I<Object> arr2 = (t) -> s.toString();
+    }
+
+}

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

@@ -220,6 +220,10 @@ public class LambdaHighlightingTest extends LightDaemonAnalyzerTestCase {
     doTest();
   }
 
+  public void testVoidCompatibility() throws Exception {
+    doTest();
+  }
+
   private void doTest() throws Exception {
     doTest(false);
   }