guava type migration: convert function variable that defined as method reference IDEA-152415

java/typeMigration/src/com/intellij/refactoring/typeMigration/rules/guava/BaseGuavaTypeConversionRule.java

@@ -101,10 +101,18 @@ public abstract class BaseGuavaTypeConversionRule extends TypeConversionRule {
       final PsiAnonymousClass anonymousClass = ((PsiNewExpression)context).getAnonymousClass();
       return anonymousClass == null ? null : findConversionForAnonymous(anonymousClass, labeler.getSettings(GuavaConversionSettings.class));
     }
-    else if (context instanceof PsiReferenceExpression) {
-      final PsiElement resolvedElement = ((PsiReferenceExpression)context).resolve();
-      if (resolvedElement instanceof PsiVariable) {
-        return findConversionForVariableReference((PsiReferenceExpression)context, (PsiVariable)resolvedElement, context);
+    else if (context instanceof PsiMethodReferenceExpression) {
+      final PsiType methodReferenceType = context.getType();
+      if (methodReferenceType != null && to != null && to.isAssignableFrom(methodReferenceType)) {
+        return new TypeConversionDescriptorBase();
+      }
+    }
+    else {
+      if (context instanceof PsiReferenceExpression) {
+        final PsiElement resolvedElement = ((PsiReferenceExpression)context).resolve();
+        if (resolvedElement instanceof PsiVariable) {
+          return findConversionForVariableReference((PsiReferenceExpression)context, (PsiVariable)resolvedElement, context);
+        }
       }
     }
     return null;

java/typeMigration/test/com/intellij/codeInsight/inspections/GuavaInspectionTest.java

@@ -286,6 +286,10 @@ public class GuavaInspectionTest extends JavaCodeInsightFixtureTestCase {
     doTestAllFile();
   }
 
+  public void testFunctionIsMethodReference() {
+    doTest();
+  }
+
   private void doTestNoQuickFixes(Class<? extends PsiElement>... highlightedElements) {
     myFixture.configureByFile(getTestName(true) + ".java");
 

java/typeMigration/testData/inspections/guava/functionIsMethodReference.java

@@ -0,0 +1,8 @@
+import com.google.common.base.Function;
+
+public class MethodReference {
+  public void context() {
+    Function<String, Integer> fun<caret>ction2 = String::length;
+
+  }
+}

java/typeMigration/testData/inspections/guava/functionIsMethodReference_after.java

@@ -0,0 +1,8 @@
+import java.util.function.Function;
+
+public class MethodReference {
+  public void context() {
+    Function<String, Integer> function2 = String::length;
+
+  }
+}