Java: When generating return statement where the returned type is an array suggest Collection.toArray() if there's no better option (IDEA-163341)

java/java-impl/src/com/intellij/codeInsight/daemon/impl/quickfix/AddReturnFix.java

@@ -16,13 +16,16 @@
 package com.intellij.codeInsight.daemon.impl.quickfix;
 
 import com.intellij.codeInsight.daemon.QuickFixBundle;
+import com.intellij.codeInsight.daemon.impl.analysis.JavaGenericsUtil;
 import com.intellij.codeInsight.intention.IntentionAction;
 import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.project.Project;
 import com.intellij.psi.*;
+import com.intellij.psi.util.InheritanceUtil;
 import com.intellij.psi.util.PsiTypesUtil;
 import com.intellij.util.containers.ContainerUtil;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -82,9 +85,33 @@ public class AddReturnFix implements IntentionAction {
         return variable.getName();
       }
     }
+    // then try to find a conversion of local variable to the required type
+    for (PsiVariable variable : variables) {
+      String conversion = getConversionToType(variable, type);
+      if (conversion != null) {
+        return conversion;
+      }
+    }
     return PsiTypesUtil.getDefaultValueOfType(type);
   }
 
+  private String getConversionToType(@NotNull PsiVariable variable, @Nullable PsiType type) {
+    PsiType varType = variable.getType();
+    if (type instanceof PsiArrayType && InheritanceUtil.isInheritor(varType, CommonClassNames.JAVA_UTIL_COLLECTION)) {
+      PsiType collectionItemType = JavaGenericsUtil.getCollectionItemType(varType, myMethod.getResolveScope());
+      if (collectionItemType != null) {
+        PsiType arrayComponentType = ((PsiArrayType)type).getComponentType();
+        if (arrayComponentType.isAssignableFrom(collectionItemType)) {
+          if (arrayComponentType.equalsToText(CommonClassNames.JAVA_LANG_OBJECT)) {
+            return variable.getName() + ".toArray()";
+          }
+          return variable.getName() + ".toArray(new " + arrayComponentType.getCanonicalText() + "[0])";
+        }
+      }
+    }
+    return null;
+  }
+
   private static PsiVariable[] getDeclaredVariables(PsiMethod method) {
     List<PsiVariable> variables = new ArrayList<>();
     PsiStatement[] statements = method.getBody().getStatements();

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/addReturn/afterArray1.java

@@ -0,0 +1,9 @@
+// "Add 'return' statement" "true"
+import java.util.*;
+class T {
+    String[] f() {
+        List<String> list = new ArrayList<>();
+        list.add("a");
+        return <caret><selection>list.toArray(new String[0])</selection>;
+    }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/addReturn/afterArray2.java

@@ -0,0 +1,9 @@
+// "Add 'return' statement" "true"
+import java.util.*;
+class T {
+    Object[] f() {
+        Set set = new HashSet();
+        set.add("a");
+        return <caret><selection>set.toArray()</selection>;
+    }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/addReturn/afterArray3.java

@@ -0,0 +1,11 @@
+// "Add 'return' statement" "true"
+import java.util.*;
+class T {
+    A[] f() {
+        Queue<B> queue = new ArrayDeque<>();
+        queue.add(new B());
+        return <caret><selection>queue.toArray(new A[0])</selection>;
+    }
+}
+class A {}
+class B extends A {}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/addReturn/beforeArray1.java

@@ -0,0 +1,8 @@
+// "Add 'return' statement" "true"
+import java.util.*;
+class T {
+    String[] f() {
+        List<String> list = new ArrayList<>();
+        list.add("a");
+        <caret>}
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/addReturn/beforeArray2.java

@@ -0,0 +1,8 @@
+// "Add 'return' statement" "true"
+import java.util.*;
+class T {
+    Object[] f() {
+        Set set = new HashSet();
+        set.add("a");
+        <caret>}
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/addReturn/beforeArray3.java

@@ -0,0 +1,10 @@
+// "Add 'return' statement" "true"
+import java.util.*;
+class T {
+    A[] f() {
+        Queue<B> queue = new ArrayDeque<>();
+        queue.add(new B());
+        <caret>}
+}
+class A {}
+class B extends A {}