completion of constructor refs (IDEA-145281)

java/java-impl/src/com/intellij/codeInsight/completion/FunctionalExpressionCompletionProvider.java

@@ -134,6 +134,23 @@ public class FunctionalExpressionCompletionProvider extends CompletionProvider<C
               collectVariantsByReceiver(prioritize, functionalInterfaceType, params, originalPosition, substitutor, expectedReturnType, result);
             }
             collectThisVariants(functionalInterfaceType, params, originalPosition, substitutor, expectedReturnType, result);
+            final PsiClass psiClass = PsiUtil.resolveClassInType(expectedReturnType);
+            if (psiClass != null) {
+              if (expectedReturnType.getArrayDimensions() == 0) {
+                final PsiMethod[] constructors = psiClass.getConstructors();
+                for (PsiMethod psiMethod : constructors) {
+                  if (areParameterTypesAppropriate(psiMethod, params, substitutor, 0)) {
+                    result.add(createConstructorReferenceLookup(functionalInterfaceType, expectedReturnType));
+                  }
+                }
+                if (constructors.length == 0 && params.length == 0) {
+                  result.add(createConstructorReferenceLookup(functionalInterfaceType, expectedReturnType));
+                }
+              }
+              else if (params.length == 1 && PsiType.INT.equals(params[0].getType())){
+                result.add(createConstructorReferenceLookup(functionalInterfaceType, expectedReturnType));
+              }
+            }
           }
         }
       }
@@ -141,6 +158,14 @@ public class FunctionalExpressionCompletionProvider extends CompletionProvider<C
     return result;
   }
 
+  private static LookupElement createConstructorReferenceLookup(PsiType functionalInterfaceType, PsiType expectedReturnType) {
+    return LookupElementBuilder
+                      .create(expectedReturnType.getPresentableText() + "::new")
+                      .withTypeText(functionalInterfaceType.getPresentableText())
+                      .withIcon(AllIcons.Nodes.MethodReference)
+                      .withAutoCompletionPolicy(AutoCompletionPolicy.NEVER_AUTOCOMPLETE);
+  }
+
   private static void collectThisVariants(PsiType functionalInterfaceType,
                                           PsiParameter[] params,
                                           PsiElement originalPosition,

java/java-tests/testSrc/com/intellij/codeInsight/daemon/lambda/Normal8CompletionTest.groovy

@@ -148,6 +148,42 @@ class Test88 {
 }
 """
   }
+  
+  public void "test constructor ref without start"() {
+    myFixture.configureByText "a.java", """
+interface Foo9 {
+  Bar test(int p);
+}
+
+class Bar {
+  public Bar(int p) {}
+}
+
+class Test88 {
+  {
+    Foo9 f = <caret>;
+  }
+}
+"""
+    def items = myFixture.completeBasic()
+    assert items.find {LookupElementPresentation.renderElement(it).itemText.contains('Bar::new')}
+  }
+  
+  public void "test new array ref"() {
+    myFixture.configureByText "a.java", """
+interface Foo9<T> {
+  T test(int p);
+}
+
+class Test88 {
+  {
+    Foo9<String[]> f = <caret>;
+  }
+}
+"""
+    def items = myFixture.completeBasic()
+    assert items.find {LookupElementPresentation.renderElement(it).itemText.contains('String[]::new')}
+  }
 
   public void testCollectorsToList() {
     configureByTestName()