make smart completion work in java extends/implements clauses (IDEA-38166)

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

@@ -33,6 +33,7 @@ import com.intellij.psi.filters.types.AssignableFromFilter;
 import com.intellij.psi.filters.types.AssignableToFilter;
 import com.intellij.psi.infos.CandidateInfo;
 import com.intellij.psi.util.PsiTreeUtil;
+import com.intellij.psi.util.proximity.ReferenceListWeigher;
 import com.intellij.util.*;
 import com.intellij.util.containers.ContainerUtil;
 import gnu.trove.THashSet;
@@ -79,7 +80,7 @@ public class JavaSmartCompletionContributor extends CompletionContributor {
       psiElement().withText(")").withParent(PsiTypeCastExpression.class)));
 
   @Nullable
-  private static ElementFilter getClassReferenceFilter(PsiElement element) {
+  private static ElementFilter getClassReferenceFilter(final PsiElement element, final boolean inRefList) {
     //throw new foo
     if (AFTER_THROW_NEW.accepts(element)) {
       return THROWABLES_FILTER;
@@ -98,15 +99,25 @@ public class JavaSmartCompletionContributor extends CompletionContributor {
       }
     }
 
+    // extends/implements/throws
+    if (inRefList) {
+      return new ElementExtractorFilter(new ElementFilter() {
+        @Override
+        public boolean isAcceptable(Object aClass, @Nullable PsiElement context) {
+          return aClass instanceof PsiClass && ReferenceListWeigher.INSTANCE.getApplicability((PsiClass)aClass, element) !=
+                                               ReferenceListWeigher.ReferenceListApplicability.inapplicable;
+        }
+
+        @Override
+        public boolean isClassAcceptable(Class hintClass) {
+          return true;
+        }
+      });
+    }
+
     return null;
   }
 
-  private static boolean isInsideThrowsList(PsiElement element) {
-    PsiMethod method = PsiTreeUtil.getParentOfType(element, PsiMethod.class);
-    return method != null && PsiTreeUtil.isAncestor(method.getThrowsList(), element, true);
-  }
-
-
   public JavaSmartCompletionContributor() {
     extend(CompletionType.SMART, SmartCastProvider.TYPECAST_TYPE_CANDIDATE, new SmartCastProvider());
 
@@ -125,16 +136,13 @@ public class JavaSmartCompletionContributor extends CompletionContributor {
         final PsiJavaCodeReferenceElement reference = 
           PsiTreeUtil.findElementOfClassAtOffset(element.getContainingFile(), parameters.getOffset(), PsiJavaCodeReferenceElement.class, false);
         if (reference != null) {
-          ElementFilter filter = getClassReferenceFilter(element);
-          boolean completeConstructor = filter != null;
-          if (filter == null && isInsideThrowsList(element)) {
-            filter = THROWABLES_FILTER;
-          }
+          boolean inRefList = ReferenceListWeigher.INSIDE_REFERENCE_LIST.accepts(element);
+          ElementFilter filter = getClassReferenceFilter(element, inRefList);
           if (filter != null) {
             final List<ExpectedTypeInfo> infos = Arrays.asList(getExpectedTypes(parameters));
             for (LookupElement item : completeReference(element, reference, filter, true, false, parameters, result.getPrefixMatcher())) {
               if (item.getObject() instanceof PsiClass) {
-                if (completeConstructor) {
+                if (!inRefList) {
                   item = LookupElementDecorator.withInsertHandler(item, ConstructorInsertHandler.SMART_INSTANCE);
                 }
                 result.addElement(decorate(item, infos));
@@ -150,7 +158,6 @@ public class JavaSmartCompletionContributor extends CompletionContributor {
               }
             }
           }
-
         }
       }
     });

java/java-impl/src/com/intellij/psi/util/proximity/ReferenceListWeigher.java

@@ -17,8 +17,8 @@ package com.intellij.psi.util.proximity;
 
 import com.intellij.openapi.roots.ProjectFileIndex;
 import com.intellij.openapi.vfs.VirtualFile;
+import com.intellij.patterns.ElementPattern;
 import com.intellij.patterns.PlatformPatterns;
-import com.intellij.patterns.PsiElementPattern;
 import com.intellij.psi.*;
 import com.intellij.psi.util.InheritanceUtil;
 import com.intellij.psi.util.ProximityLocation;
@@ -33,7 +33,7 @@ import static com.intellij.psi.util.proximity.ReferenceListWeigher.ReferenceList
 public class ReferenceListWeigher extends ProximityWeigher {
   public static final ReferenceListWeigher INSTANCE = new ReferenceListWeigher();
 
-  private static final PsiElementPattern.Capture<PsiElement> INSIDE_REFERENCE_LIST =
+  public static final ElementPattern<PsiElement> INSIDE_REFERENCE_LIST =
     PlatformPatterns.psiElement().withParents(PsiJavaCodeReferenceElement.class, PsiReferenceList.class);
 
   protected enum Preference {

java/java-tests/testData/codeInsight/completion/smartType/OnlyInterfacesInImplements-out.java

@@ -0,0 +1,7 @@
+public class Main implements XFooIntf<caret> {
+
+}
+
+class XFoo1 {}
+class XFoo2 {}
+interface XFooIntf {}

java/java-tests/testData/codeInsight/completion/smartType/OnlyInterfacesInImplements.java

@@ -0,0 +1,7 @@
+public class Main implements XF<caret> {
+
+}
+
+class XFoo1 {}
+class XFoo2 {}
+interface XFooIntf {}

java/java-tests/testSrc/com/intellij/codeInsight/completion/SmartTypeCompletionTest.java

@@ -1159,6 +1159,8 @@ public class SmartTypeCompletionTest extends LightFixtureCompletionTestCase {
 
   public void testSuggestCastReturnTypeByCalledMethod() { doTest(); }
 
+  public void testOnlyInterfacesInImplements() { doTest(); }
+
   public void testNonStaticField() throws Exception { doAntiTest(); }
 
   private void doActionTest() throws Exception {