lambda completion: strip unnecessary parenthesis, generate parameter names as for override/implement (IDEA-121947)

(cherry picked from commit 273ae0329f28a5bec42847a8739faf8a815cab37)

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

@@ -16,13 +16,16 @@
 package com.intellij.codeInsight.completion;
 
 import com.intellij.codeInsight.ExpectedTypeInfo;
+import com.intellij.codeInsight.generation.GenerateMembersUtil;
 import com.intellij.codeInsight.lookup.AutoCompletionPolicy;
 import com.intellij.codeInsight.lookup.LookupElement;
 import com.intellij.codeInsight.lookup.LookupElementBuilder;
 import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.editor.EditorModificationUtil;
+import com.intellij.openapi.project.Project;
 import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.psi.*;
+import com.intellij.psi.codeStyle.JavaCodeStyleManager;
 import com.intellij.psi.util.PsiUtil;
 import com.intellij.util.Function;
 import com.intellij.util.ProcessingContext;
@@ -43,8 +46,17 @@ public class LambdaCompletionProvider extends CompletionProvider<CompletionParam
       if (LambdaUtil.isFunctionalType(defaultType)) {
         final PsiMethod method = LambdaUtil.getFunctionalInterfaceMethod(defaultType);
         if (method != null) {
-          final PsiParameter[] params = method.getParameterList().getParameters();
-          final String paramsString = "(" + StringUtil.join(params, new Function<PsiParameter, String>() {
+          PsiParameter[] params = method.getParameterList().getParameters();
+          final Project project = method.getProject();
+          final PsiElement originalPosition = parameters.getOriginalPosition();
+          final JVMElementFactory jvmElementFactory = originalPosition != null ? JVMElementFactories.getFactory(originalPosition.getLanguage(), project) : null;
+          if (jvmElementFactory != null) {
+            final PsiSubstitutor substitutor = LambdaUtil.getSubstitutor(method, PsiUtil.resolveGenericsClassInType(defaultType));
+            final JavaCodeStyleManager codeStyleManager = JavaCodeStyleManager.getInstance(project);
+            params = GenerateMembersUtil.overriddenParameters(params, jvmElementFactory, codeStyleManager, substitutor, originalPosition);
+          }
+
+          final String paramsString = params.length == 1 ? params[0].getName() : "(" + StringUtil.join(params, new Function<PsiParameter, String>() {
             @Override
             public String fun(PsiParameter parameter) {
               return parameter.getName();

java/java-impl/src/com/intellij/codeInsight/generation/GenerateMembersUtil.java

@@ -385,10 +385,25 @@ public class GenerateMembersUtil {
                                            @NotNull PsiParameterList sourceParameterList,
                                            @NotNull PsiParameterList targetParameterList,
                                            @NotNull PsiSubstitutor substitutor, PsiElement target) {
-    PsiParameter[] parameters = sourceParameterList.getParameters();
+    final PsiParameter[] parameters = sourceParameterList.getParameters();
+    final PsiParameter[] newParameters = overriddenParameters(parameters, factory, codeStyleManager, substitutor, target);
+    for (int i = 0; i < newParameters.length; i++) {
+      final PsiParameter newParameter = newParameters[i];
+      copyOrReplaceModifierList(parameters[i], newParameter);
+      targetParameterList.add(newParameter);
+    }
+  }
+
+  public static PsiParameter[] overriddenParameters(PsiParameter[] parameters,
+                                                    @NotNull JVMElementFactory factory,
+                                                    @NotNull JavaCodeStyleManager codeStyleManager,
+                                                    @NotNull PsiSubstitutor substitutor,
+                                                    PsiElement target) {
+    PsiParameter[] result = new PsiParameter[parameters.length];
     UniqueNameGenerator generator = new UniqueNameGenerator();
 
-    for (PsiParameter parameter : parameters) {
+    for (int i = 0; i < parameters.length; i++) {
+      PsiParameter parameter = parameters[i];
       final PsiType parameterType = parameter.getType();
       final PsiType substituted = substituteType(substitutor, parameterType, (PsiMethod)parameter.getDeclarationScope());
       @NonNls String paramName = parameter.getName();
@@ -413,10 +428,9 @@ public class GenerateMembersUtil {
         paramName = generator.generateUniqueName(paramName);
       }
       generator.addExistingName(paramName);
-      final PsiParameter newParameter = factory.createParameter(paramName, substituted, target);
-      copyOrReplaceModifierList(parameter, newParameter);
-      targetParameterList.add(newParameter);
+      result[i] = factory.createParameter(paramName, substituted, target);
     }
+    return result;
   }
 
   private static void substituteThrows(@NotNull JVMElementFactory factory,

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

@@ -0,0 +1,9 @@
+interface I<T> {
+  void m(T t);
+}
+
+class Test {
+  public static void main(String[] args) {
+    I<String> i = s -> <caret>
+  }
+}

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

@@ -0,0 +1,9 @@
+interface I<T> {
+  void m(T t);
+}
+
+class Test {
+  public static void main(String[] args) {
+    I<String> i = <caret>
+  }
+}

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

@@ -0,0 +1,9 @@
+interface I {
+  void m(int x);
+}
+
+class Test {
+  public static void main(String[] args) {
+    I i = x -> <caret>
+  }
+}

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

@@ -0,0 +1,9 @@
+interface I {
+  void m(int x);
+}
+
+class Test {
+  public static void main(String[] args) {
+    I i = <caret>
+  }
+}

java/java-tests/testSrc/com/intellij/codeInsight/completion/SmartType18CompletionTest.java

@@ -73,6 +73,14 @@ public class SmartType18CompletionTest extends LightFixtureCompletionTestCase {
     doTest();
   }
 
+  public void testInLambdaPositionSingleParam() throws Exception {
+    doTest();
+  }
+
+  public void testInLambdaPositionNameSubstitution() throws Exception {
+    doTest();
+  }
+
   public void testFilteredMethodReference() throws Exception {
     doTest();
   }