Intention to replace add/addAll on a mutable collection with += (#1143)

idea/src/META-INF/plugin.xml

@@ -1603,6 +1603,11 @@
       <category>Kotlin</category>
     </intentionAction>
 
+    <intentionAction>
+      <className>org.jetbrains.kotlin.idea.intentions.ReplaceAddWithPlusAssignIntention</className>
+      <category>Kotlin</category>
+    </intentionAction>
+
     <localInspection implementationClass="org.jetbrains.kotlin.idea.intentions.ObjectLiteralToLambdaInspection"
                      displayName="Object literal can be converted to lambda"
                      groupPath="Kotlin"

idea/src/org/jetbrains/kotlin/idea/intentions/ReplaceAddWithPlusAssignIntention.kt

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2010-2017 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.idea.intentions
+
+import com.intellij.openapi.editor.Editor
+import org.jetbrains.kotlin.builtins.DefaultBuiltIns
+import org.jetbrains.kotlin.idea.caches.resolve.analyze
+import org.jetbrains.kotlin.psi.KtDotQualifiedExpression
+import org.jetbrains.kotlin.psi.KtPsiFactory
+import org.jetbrains.kotlin.psi.createExpressionByPattern
+import org.jetbrains.kotlin.resolve.BindingContextUtils
+import org.jetbrains.kotlin.resolve.DescriptorUtils
+import org.jetbrains.kotlin.resolve.calls.callUtil.getResolvedCall
+import org.jetbrains.kotlin.resolve.calls.resolvedCallUtil.getExplicitReceiverValue
+import org.jetbrains.kotlin.resolve.descriptorUtil.isSubclassOf
+import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
+
+class ReplaceAddWithPlusAssignIntention : SelfTargetingOffsetIndependentIntention<KtDotQualifiedExpression>(KtDotQualifiedExpression::class.java, "Replace with '+='") {
+    override fun isApplicableTo(element: KtDotQualifiedExpression): Boolean {
+        if (element.callExpression?.valueArguments?.size != 1) return false
+
+        when (element.calleeName) {
+            "add" -> text = "Replace 'add()' with '+='"
+            "addAll" -> text = "Replace 'addAll()' with '+='"
+            else -> return false
+        }
+
+        val context = element.analyze(BodyResolveMode.PARTIAL)
+        BindingContextUtils.extractVariableDescriptorFromReference(context, element.receiverExpression)?.let {
+            if (it.isVar) return false
+        } ?: return false
+
+        val resolvedCall = element.getResolvedCall(context) ?: return false
+        val receiverClass = DescriptorUtils.getClassDescriptorForType(resolvedCall.getExplicitReceiverValue()?.type ?: return false)
+        return receiverClass.isSubclassOf(DefaultBuiltIns.Instance.mutableCollection)
+    }
+
+    override fun applyTo(element: KtDotQualifiedExpression, editor: Editor?) {
+        element.replace(KtPsiFactory(element).createExpressionByPattern("$0 += $1", element.receiverExpression,
+                                                                        element.callExpression?.valueArguments?.get(0)?.getArgumentExpression() ?: return))
+    }
+}