Extract rule: template-no-extra-mut-helpers

Author: NullVoxPopuli

README.md

@@ -199,6 +199,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-capital-arguments](docs/rules/template-no-capital-arguments.md)                           | disallow capital arguments (use lowercase @arg instead of @Arg) |    |    |    |
 | [template-no-debugger](docs/rules/template-no-debugger.md)                                             | disallow {{debugger}} in templates                              |    |    |    |
 | [template-no-element-event-actions](docs/rules/template-no-element-event-actions.md)                   | disallow element event actions (use {{on}} modifier instead)    |    |    |    |
+| [template-no-extra-mut-helpers](docs/rules/template-no-extra-mut-helpers.md)                           | disallow unnecessary mut helpers                                |    |    |    |
 | [template-no-log](docs/rules/template-no-log.md)                                                       | disallow {{log}} in templates                                   |    |    |    |
 
 ### Components

docs/rules/template-no-extra-mut-helpers.md

@@ -0,0 +1,43 @@
+# ember/template-no-extra-mut-helpers
+
+<!-- end auto-generated rule header -->
+
+Disallows unnecessary `mut` helpers.
+
+## Rule Details
+
+The `mut` helper is often unnecessary when passing simple values or properties. It should only be used when explicitly creating a mutable reference is required.
+
+## Examples
+
+Examples of **incorrect** code for this rule:
+
+```gjs
+<template>
+  <MyComponent @onChange={{mut this.value}} />
+</template>
+```
+
+```gjs
+<template>
+  <Input @value={{mut this.text}} />
+</template>
+```
+
+Examples of **correct** code for this rule:
+
+```gjs
+<template>
+  <MyComponent @value={{this.value}} />
+</template>
+```
+
+```gjs
+<template>
+  <Input @value={{this.text}} />
+</template>
+```
+
+## References
+
+- [eslint-plugin-ember template-no-extra-mut-helper-argument](https://github.com/ember-cli/eslint-plugin-ember/blob/master/docs/rules/template-no-extra-mut-helper-argument.md)

lib/rules/template-no-extra-mut-helpers.js

@@ -0,0 +1,41 @@
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow unnecessary mut helpers',
+      category: 'Best Practices',
+      strictGjs: true,
+      strictGts: true,
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-extra-mut-helpers.md',
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      unnecessaryMut: 'Unnecessary mut helper. Remove it.',
+    },
+  },
+
+  create(context) {
+    return {
+      GlimmerSubExpression(node) {
+        if (
+          node.path &&
+          node.path.type === 'GlimmerPathExpression' &&
+          node.path.original === 'mut' &&
+          node.params &&
+          node.params.length === 1
+        ) {
+          const param = node.params[0];
+          // mut is unnecessary when wrapping a simple path expression
+          if (param.type === 'GlimmerPathExpression') {
+            context.report({
+              node,
+              messageId: 'unnecessaryMut',
+            });
+          }
+        }
+      },
+    };
+  },
+};

tests/lib/rules/template-no-extra-mut-helpers.js

@@ -0,0 +1,68 @@
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const rule = require('../../../lib/rules/template-no-extra-mut-helpers');
+const RuleTester = require('eslint').RuleTester;
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('template-no-extra-mut-helpers', rule, {
+  valid: [
+    `<template>
+      <MyComponent @value={{this.value}} />
+    </template>`,
+    `<template>
+      <input value={{this.text}} />
+    </template>`,
+    `<template>
+      <div></div>
+    </template>`,
+  ],
+
+  invalid: [
+    {
+      code: `<template>
+        {{my-component onChange=(mut this.value)}}
+      </template>`,
+      output: null,
+      errors: [
+        {
+          message: 'Unnecessary mut helper. Remove it.',
+          type: 'GlimmerSubExpression',
+        },
+      ],
+    },
+    {
+      code: `<template>
+        {{input value=(mut this.text)}}
+      </template>`,
+      output: null,
+      errors: [
+        {
+          message: 'Unnecessary mut helper. Remove it.',
+          type: 'GlimmerSubExpression',
+        },
+      ],
+    },
+    {
+      code: `<template>
+        {{my-component value=(mut this.data)}}
+      </template>`,
+      output: null,
+      errors: [
+        {
+          message: 'Unnecessary mut helper. Remove it.',
+          type: 'GlimmerSubExpression',
+        },
+      ],
+    },
+  ],
+});