feature: @putout/plugin-remove-useless-variables: assignment: add

Author: coderaiser

packages/plugin-remove-useless-variables/.putout.json

@@ -1,6 +1,7 @@
 {
     "match": {
-        "README.md": {
+        "*.md": {
+            "putout/declare": "off",
             "promises/remove-useless-async": "off"
         }
     }

packages/plugin-remove-useless-variables/README.md

@@ -13,6 +13,7 @@ npm i @putout/plugin-remove-useless-variables -D
 
 ## Rules
 
+- ✅ [assignment](#assignmentn);
 - ✅ [declaration](#declaration);
 - ✅ [destruct](#destruct);
 - ✅ [duplicate](#duplicate);
@@ -24,6 +25,7 @@ npm i @putout/plugin-remove-useless-variables -D
 ```json
 {
     "rules": {
+        "remove-useless-variables/assignment": "on",
         "remove-useless-variables/rename": "on",
         "remove-useless-variables/remove": "on",
         "remove-useless-variables/destruct": "on",
@@ -35,6 +37,22 @@ npm i @putout/plugin-remove-useless-variables -D
 }
 ```
 
+## assignment
+
+Checkout in 🐊[**Putout Editor**](https://putout.cloudcmd.io/#/gist/a2f7fe5e2c294443576f95dce6fde67e/342492c8b9de8e36e469c8f543fc0f2b7d2df73c).
+
+### ❌ Example of incorrect code
+
+```js
+while (!(files = readDirectory(parentDir)).length) {}
+```
+
+### ✅ Example of correct code
+
+```js
+while (!readDirectory(parentDir).length) {}
+```
+
 ## rename
 
 ### ❌ Example of incorrect code

packages/plugin-remove-useless-variables/lib/assignment/fixture/assignment-fix.js

@@ -0,0 +1,23 @@
+function notReferenced() {
+    let files = [];
+    
+    while (!readDirectory(parentDir)) {}}
+
+function referenced() {
+    let files = [];
+    
+    while (!(files = readDirectory(parentDir)).length) {}
+    
+    console.log(files);
+}
+
+function notIdentifier() {
+    let files = [];
+    
+    while (!(files.x = readDirectory(parentDir)).length) {}}
+
+function notDeclared() {
+    while (!(files = readDirectory(parentDir)).length) {}
+    
+    console.log(files);
+}

packages/plugin-remove-useless-variables/lib/assignment/fixture/assignment.js

@@ -0,0 +1,28 @@
+function notReferenced() {
+    let files = [];
+
+    while (!(files = readDirectory(parentDir)).length) {
+    }
+}
+
+function referenced() {
+    let files = [];
+
+    while (!(files = readDirectory(parentDir)).length) {
+    }
+    
+    console.log(files);
+}
+
+function notIdentifier() {
+    let files = [];
+
+    while (!(files.x = readDirectory(parentDir)).length) {
+    }
+}
+
+function notDeclared() {
+    while (!(files = readDirectory(parentDir)).length) {
+    }
+    console.log(files);
+}

packages/plugin-remove-useless-variables/lib/assignment/index.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const {types, operator} = require('putout');
+
+const {getBinding} = operator;
+const {isIdentifier} = types;
+
+module.exports.report = () => `Avoid useless assign`;
+
+module.exports.match = () => ({
+    '(__a = __b).__c': ({__a}, path) => {
+        if (!isIdentifier(__a))
+            return false;
+        
+        const binding = getBinding(path, __a.name);
+        
+        if (!binding)
+            return false;
+        
+        const {references} = binding;
+        
+        return !references;
+    },
+});
+
+module.exports.replace = () => ({
+    '(__a = __b).__c': '__b',
+});

packages/plugin-remove-useless-variables/lib/assignment/index.spec.js

@@ -0,0 +1,20 @@
+'use strict';
+
+const {createTest} = require('@putout/test');
+const plugin = require('.');
+
+const test = createTest(__dirname, {
+    plugins: [
+        ['assignment', plugin],
+    ],
+});
+
+test('remove-useless-variables: assignment: report', (t) => {
+    t.report('assignment', `Avoid useless assign`);
+    t.end();
+});
+
+test('remove-useless-variables: assignment: transform', (t) => {
+    t.transform('assignment');
+    t.end();
+});

packages/plugin-remove-useless-variables/lib/index.js

@@ -5,11 +5,13 @@ const remove = require('./remove');
 const destruct = require('./destruct');
 const declaration = require('./declaration');
 const duplicate = require('./duplicate');
+const assignment = require('./assignment');
 
 module.exports.rules = {
     rename,
     remove,
     destruct,
     declaration,
     duplicate,
+    assignment,
 };

packages/plugin-remove-useless-variables/test/fixture/assignment-fix.js

@@ -0,0 +1,23 @@
+function notReferenced() {
+    let files = [];
+    
+    while (!readDirectory(parentDir)) {}}
+
+function referenced() {
+    let files = [];
+    
+    while (!(files = readDirectory(parentDir)).length) {}
+    
+    console.log(files);
+}
+
+function notIdentifier() {
+    let files = [];
+    
+    while (!(files.x = readDirectory(parentDir)).length) {}}
+
+function notDeclared() {
+    while (!(files = readDirectory(parentDir)).length) {}
+    
+    console.log(files);
+}

packages/plugin-remove-useless-variables/test/fixture/assignment.js

@@ -0,0 +1,28 @@
+function notReferenced() {
+    let files = [];
+
+    while (!(files = readDirectory(parentDir)).length) {
+    }
+}
+
+function referenced() {
+    let files = [];
+
+    while (!(files = readDirectory(parentDir)).length) {
+    }
+    
+    console.log(files);
+}
+
+function notIdentifier() {
+    let files = [];
+
+    while (!(files.x = readDirectory(parentDir)).length) {
+    }
+}
+
+function notDeclared() {
+    while (!(files = readDirectory(parentDir)).length) {
+    }
+    console.log(files);
+}

packages/plugin-remove-useless-variables/test/remove-useless-variables.js

@@ -78,3 +78,8 @@ test('plugin-remove-useless-variables: transform: duplicate', (t) => {
     t.transform('duplicate');
     t.end();
 });
+
+test('plugin-remove-useless-variables: transform: assignment', (t) => {
+    t.transform('assignment');
+    t.end();
+});