IDEA-128948 Smart type completion should propose generic parameter type

java/java-impl/src/com/intellij/codeInsight/CodeInsightUtil.java

@@ -16,6 +16,7 @@
 package com.intellij.codeInsight;
 
 import com.intellij.codeInsight.completion.AllClassesGetter;
+import com.intellij.codeInsight.completion.CompletionUtil;
 import com.intellij.codeInsight.completion.JavaCompletionUtil;
 import com.intellij.codeInsight.completion.PrefixMatcher;
 import com.intellij.lang.Language;
@@ -33,21 +34,21 @@ import com.intellij.psi.*;
 import com.intellij.psi.search.GlobalSearchScope;
 import com.intellij.psi.search.searches.ClassInheritorsSearch;
 import com.intellij.psi.tree.IElementType;
-import com.intellij.psi.util.PsiTreeUtil;
-import com.intellij.psi.util.PsiUtil;
-import com.intellij.psi.util.PsiUtilCore;
-import com.intellij.psi.util.TypeConversionUtil;
+import com.intellij.psi.util.*;
 import com.intellij.psi.util.proximity.PsiProximityComparator;
 import com.intellij.refactoring.util.RefactoringUtil;
 import com.intellij.util.Consumer;
 import com.intellij.util.FilteredQuery;
 import com.intellij.util.Processor;
 import com.intellij.util.Query;
-import com.intellij.psi.util.FileTypeUtils;
+import com.intellij.util.containers.ContainerUtil;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Set;
 
 public class CodeInsightUtil {
   @Nullable
@@ -283,6 +284,11 @@ public class CodeInsightUtil {
 
     final Processor<PsiClass> inheritorsProcessor =
       createInheritorsProcessor(context, baseType, arrayDim, getRawSubtypes, consumer, baseClass, baseSubstitutor);
+
+    addContextTypeArguments(context, baseType, inheritorsProcessor);
+
+    if (baseClass.hasModifierProperty(PsiModifier.FINAL)) return;
+
     if (matcher.getPrefix().length() > 2) {
       AllClassesGetter.processJavaClasses(matcher, context.getProject(), scope, new Processor<PsiClass>() {
         @Override
@@ -307,6 +313,30 @@ public class CodeInsightUtil {
 
   }
 
+  private static void addContextTypeArguments(final PsiElement context,
+                                              final PsiClassType baseType,
+                                              final Processor<PsiClass> inheritorsProcessor) {
+    ApplicationManager.getApplication().runReadAction(new Runnable() {
+      @Override
+      public void run() {
+        Set<String> usedNames = ContainerUtil.newHashSet();
+        PsiElementFactory factory = JavaPsiFacade.getElementFactory(context.getProject());
+        PsiElement each = context;
+        while (true) {
+          PsiTypeParameterListOwner typed = PsiTreeUtil.getParentOfType(each, PsiTypeParameterListOwner.class);
+          if (typed == null) break;
+          for (PsiTypeParameter parameter : typed.getTypeParameters()) {
+            if (baseType.isAssignableFrom(factory.createType(parameter)) && usedNames.add(parameter.getName())) {
+              inheritorsProcessor.process(CompletionUtil.getOriginalOrSelf(parameter));
+            }
+          }
+
+          each = typed;
+        }
+      }
+    });
+  }
+
   public static Processor<PsiClass> createInheritorsProcessor(final PsiElement context, final PsiClassType baseType,
                                                                final int arrayDim,
                                                                final boolean getRawSubtypes,

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

@@ -278,10 +278,12 @@ public class JavaCompletionSorting {
 
     @NotNull
     @Override
-    public Comparable weigh(@NotNull LookupElement item) {
+    public MyResult weigh(@NotNull LookupElement item) {
       final Object object = item.getObject();
 
       if (object instanceof PsiClass) {
+        if (object instanceof PsiTypeParameter) return MyResult.typeParameter;
+
         if (myTypeParameter != null && object.equals(PsiUtil.resolveClassInType(TypeConversionUtil.typeParameterErasure(myTypeParameter)))) {
           return MyResult.exactlyExpected;
         }
@@ -340,6 +342,7 @@ public class JavaCompletionSorting {
 
     private enum MyResult {
       expectedNoSelect,
+      typeParameter,
       exactlyDefault,
       ofDefaultType,
       exactlyExpected,

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

@@ -229,10 +229,7 @@ public class JavaInheritorsGetter extends CompletionProvider<CompletionParameter
 
     //long
     for (final PsiClassType type : expectedClassTypes) {
-      final PsiClass psiClass = type.resolve();
-      if (psiClass != null && !psiClass.hasModifierProperty(PsiModifier.FINAL)) {
-        CodeInsightUtil.processSubTypes(type, parameters.getPosition(), false, matcher, consumer);
-      }
+      CodeInsightUtil.processSubTypes(type, parameters.getPosition(), false, matcher, consumer);
     }
   }
 

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

@@ -158,8 +158,9 @@ public class JavaSmartCompletionContributor extends CompletionContributor {
             @Override
             public void consume(PsiType type) {
               final PsiClass psiClass = PsiUtil.resolveClassInType(type);
-              if (psiClass == null) return;
+              if (psiClass == null || psiClass instanceof PsiTypeParameter) return;
 
+              //noinspection SuspiciousMethodCalls
               if (expectedClassTypes.contains(type)) return;
 
               result.addElement(createInstanceofLookupElement(psiClass, parameterizedTypes));

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

@@ -307,3 +307,4 @@ public interface JVMElementFactory {
    */
   boolean isValidLocalVariableName(@NotNull String name);
 }
+

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

@@ -0,0 +1,8 @@
+class StringEx<T extends String> {
+}
+class Outer<T extends String> {
+  static class CompletionTest<T extends String> {
+    private StringEx<<caret>> myString;
+  }
+}
+

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

@@ -777,6 +777,11 @@ public class SmartTypeCompletionTest extends LightFixtureCompletionTestCase {
     myFixture.assertPreferredCompletionItems(0, "i", "z", "zz", "i, z, zz");
   }
 
+  public void testSuggestTypeParametersInTypeArgumentList() {
+    configureByTestName();
+    myFixture.assertPreferredCompletionItems(0, "T", "String");
+  }
+
   public void testWrongAnonymous() throws Throwable {
     configureByTestName();
     select();