java completion: remove irrelevant suggestions after Unresolved:: (IDEA-201798)

to enable chain completion, which only works when there are no other suggestions

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

@@ -34,6 +34,7 @@ import static com.intellij.psi.SyntaxTraverser.psiApi;
 
 public class JavaKeywordCompletion {
   public static final ElementPattern<PsiElement> AFTER_DOT = psiElement().afterLeaf(".");
+  private static final ElementPattern<PsiElement> AFTER_DOUBLE_COLON = psiElement().afterLeaf("::");
 
   static final ElementPattern<PsiElement> VARIABLE_AFTER_FINAL = psiElement().afterLeaf(PsiKeyword.FINAL).inside(PsiDeclarationStatement.class);
 
@@ -417,10 +418,12 @@ public class JavaKeywordCompletion {
   }
 
   private void addExpressionKeywords(boolean statementPosition) {
-    if (psiElement(JavaTokenType.DOUBLE_COLON).accepts(myPrevLeaf)) {
+    if (AFTER_DOUBLE_COLON.accepts(myPosition)) {
       PsiMethodReferenceExpression parent = PsiTreeUtil.getParentOfType(myPosition, PsiMethodReferenceExpression.class);
-      TailType tail = parent != null && !LambdaHighlightingUtil.insertSemicolon(parent.getParent()) ? TailType.SEMICOLON : TailType.NONE;
-      addKeyword(new OverridableSpace(createKeyword(PsiKeyword.NEW), tail));
+      if (parent != null && canUseConstructorReference(parent)) {
+        TailType tail = !LambdaHighlightingUtil.insertSemicolon(parent.getParent()) ? TailType.SEMICOLON : TailType.NONE;
+        addKeyword(new OverridableSpace(createKeyword(PsiKeyword.NEW), tail));
+      }
       return;
     }
 
@@ -442,6 +445,17 @@ public class JavaKeywordCompletion {
     }
   }
 
+  private static boolean canUseConstructorReference(PsiMethodReferenceExpression ref) {
+    PsiTypeElement qualifierType = ref.getQualifierType();
+    if (qualifierType == null) {
+      PsiElement qualifier = ref.getQualifier();
+      return qualifier instanceof PsiJavaCodeReferenceElement && ((PsiJavaCodeReferenceElement)qualifier).resolve() != null;
+    }
+
+    if (qualifierType instanceof PsiClassType) return ((PsiClassType)qualifierType).resolve() != null;
+    return qualifierType instanceof PsiArrayType;
+  }
+
   private boolean isQualifiedNewContext() {
     if (myPosition.getParent() instanceof PsiReferenceExpression) {
       PsiExpression qualifier = ((PsiReferenceExpression)myPosition.getParent()).getQualifierExpression();
@@ -644,6 +658,7 @@ public class JavaKeywordCompletion {
 
   static void addPrimitiveTypes(Consumer<? super LookupElement> result, PsiElement position, JavaCompletionSession session) {
     if (AFTER_DOT.accepts(position) ||
+        AFTER_DOUBLE_COLON.accepts(position) ||
         psiElement().inside(psiAnnotation()).accepts(position) && !expectsClassLiteral(position)) {
       return;
     }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/completion/normal/ChainedMethodReferenceWithNoPrefix.java

@@ -0,0 +1,5 @@
+class A {
+  {
+    Runnable r = Strings::<caret>
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInsight/completion/Normal8CompletionTest.groovy

@@ -340,6 +340,13 @@ class Test88 {
     checkResultByFileName()
   }
 
+  void testChainedMethodReferenceWithNoPrefix() {
+    myFixture.addClass("package bar; public class Strings {}")
+    myFixture.addClass("package foo; public class Strings { public static void goo() {} }")
+    configureByTestName()
+    myFixture.assertPreferredCompletionItems 0, 'Strings::goo'
+  }
+
   void testPreferVariableToLambda() {
     configureByTestName()
     myFixture.assertPreferredCompletionItems 0, 'output', 'out -> '