Extract rule: template-simple-modifiers

README.md

@@ -245,6 +245,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-obsolete-elements](docs/rules/template-no-obsolete-elements.md)                                 | disallow obsolete HTML elements                                              |    |    |    |
 | [template-no-outlet-outside-routes](docs/rules/template-no-outlet-outside-routes.md)                         | disallow {{outlet}} outside of route templates                               |    |    |    |
 | [template-no-page-title-component](docs/rules/template-no-page-title-component.md)                           | disallow usage of ember-page-title component                                 |    |    |    |
+| [template-simple-modifiers](docs/rules/template-simple-modifiers.md)                                         | require simple modifier syntax                                               |    |    |    |
 | [template-simple-unless](docs/rules/template-simple-unless.md)                                               | require simple conditions in unless blocks                                   |    |    |    |
 | [template-splat-attributes-only](docs/rules/template-splat-attributes-only.md)                               | disallow ...spread other than ...attributes                                  |    |    |    |
 | [template-style-concatenation](docs/rules/template-style-concatenation.md)                                   | disallow string concatenation in inline styles                               |    |    |    |

docs/rules/template-simple-modifiers.md

@@ -0,0 +1,60 @@
+# ember/template-simple-modifiers
+
+<!-- end auto-generated rule header -->
+
+Require simple modifier syntax.
+
+This rule strongly advises against passing complex statements or conditionals to the
+first argument of the `{{modifier}}` helper. Instead, the first argument should be
+either:
+
+- a string literal such as `{{(modifier "track-interaction")}}`
+- a path expression such as `{{(modifier this.trackInteraction)}}`
+
+A common issue this rule catches is declaring the modifier name conditionally, which
+works because `modifier` ignores `null` and `undefined`, but makes the intent much
+harder to read. Prefer placing the conditional around the modifier invocation instead.
+
+## Examples
+
+This rule **forbids** the following:
+
+```gjs
+<template>
+  <div
+    {{(modifier
+      (unless this.hasBeenClicked 'track-interaction')
+      'click'
+      customizeData=this.customizeClickData
+    )}}
+  ></div>
+</template>
+```
+
+```gjs
+<template>
+  <div {{(modifier)}}></div>
+</template>
+```
+
+This rule **allows** the following:
+
+```gjs
+<template>
+  <div
+    {{(unless
+      this.hasBeenClicked
+      (modifier 'track-interaction' 'click' customizeData=this.customizeClickData)
+    )}}
+  ></div>
+</template>
+```
+
+## Why?
+
+Using complex expressions as the modifier name reduces readability and makes it harder
+to understand which modifier is being applied.
+
+## References
+
+- [Ember.js Guides - Modifiers](https://guides.emberjs.com/release/components/template-lifecycle-dom-and-modifiers/#toc_event-handlers)

lib/rules/template-simple-modifiers.js

@@ -0,0 +1,62 @@
+function isModifierHelper(node) {
+  return node.path?.original === 'modifier';
+}
+
+function isValidFirstParam(node) {
+  return (
+    node.type === 'GlimmerStringLiteral' || (node.type === 'GlimmerPathExpression' && node.original)
+  );
+}
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'require simple modifier syntax',
+      category: 'Best Practices',
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-simple-modifiers.md',
+      templateMode: 'both',
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      invalidFirstArgument:
+        'The modifier helper should have a string or a variable name containing the modifier name as a first argument.',
+    },
+    originallyFrom: {
+      name: 'ember-template-lint',
+      rule: 'lib/rules/simple-modifiers.js',
+      docs: 'docs/rule/simple-modifiers.md',
+      tests: 'test/unit/rules/simple-modifiers-test.js',
+    },
+  },
+
+  create(context) {
+    return {
+      // This catches {{(modifier ...)}} expressions
+      GlimmerSubExpression(node) {
+        if (!isModifierHelper(node)) {
+          return;
+        }
+
+        const firstParam = node.params?.[0];
+
+        if (!firstParam) {
+          context.report({
+            node,
+            messageId: 'invalidFirstArgument',
+          });
+          return;
+        }
+
+        if (!isValidFirstParam(firstParam)) {
+          context.report({
+            node: firstParam,
+            messageId: 'invalidFirstArgument',
+          });
+        }
+      },
+    };
+  },
+};

tests/lib/rules/template-simple-modifiers.js

@@ -0,0 +1,89 @@
+const rule = require('../../../lib/rules/template-simple-modifiers');
+const RuleTester = require('eslint').RuleTester;
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('template-simple-modifiers', rule, {
+  valid: [
+    '<template><div {{(modifier "track-interaction" @controlName)}}></div></template>',
+    '<template><div {{(modifier trackInteraction @controlName)}}></div></template>',
+    '<template><div {{(modifier this.trackInteraction @controlName)}}></div></template>',
+    '<template><div {{my-modifier}}></div></template>',
+
+    '<template><div {{(modifier @trackInteraction @controlName)}}></div></template>',
+    '<template><div {{(if @isActionVisible (modifier "track-interaction" eventName=myEventName eventBody=myEventbody))}}></div></template>',
+    '<template><div {{(my-modifier (unless this.hasBeenClicked "track-interaction") "click" customizeData=this.customizeClickData)}}></div></template>',
+    '<template><MyComponent @people={{array "Tom Dale" "Yehuda Katz" this.myOtherPerson}} /></template>',
+    '<template><div {{(if this.foo (modifier "foo-bar"))}}></div></template>',
+  ],
+  invalid: [
+    {
+      code: '<template><div {{(modifier)}}></div></template>',
+      output: null,
+      errors: [
+        {
+          message:
+            'The modifier helper should have a string or a variable name containing the modifier name as a first argument.',
+        },
+      ],
+    },
+
+    {
+      code: '<template><div {{(modifier (unless this.hasBeenClicked "track-interaction") "click" customizeData=this.customizeClickData)}}></div></template>',
+      output: null,
+      errors: [
+        {
+          message:
+            'The modifier helper should have a string or a variable name containing the modifier name as a first argument.',
+        },
+      ],
+    },
+  ],
+});
+
+const hbsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser/hbs'),
+  parserOptions: {
+    ecmaVersion: 2022,
+    sourceType: 'module',
+  },
+});
+
+hbsRuleTester.run('template-simple-modifiers', rule, {
+  valid: [
+    '<div {{(modifier "track-interaction" @controlName)}}></div>',
+    '<div {{(modifier trackInteraction @controlName)}}></div>',
+    '<div {{(modifier this.trackInteraction @controlName)}}></div>',
+    '<div {{(modifier @trackInteraction @controlName)}}></div>',
+    '<div {{(if @isActionVisible (modifier "track-interaction" eventName=myEventName eventBody=myEventbody))}}></div>',
+    '<div {{(my-modifier (unless this.hasBeenClicked "track-interaction") "click" customizeData=this.customizeClickData)}}></div>',
+    '<div {{my-modifier}}></div>',
+    '<MyComponent @people={{array "Tom Dale" "Yehuda Katz" this.myOtherPerson}} />',
+    '<div {{(if this.foo (modifier "foo-bar"))}}></div>',
+  ],
+  invalid: [
+    {
+      code: '<div {{(modifier (unless this.hasBeenClicked "track-interaction") "click" customizeData=this.customizeClickData)}}></div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'The modifier helper should have a string or a variable name containing the modifier name as a first argument.',
+        },
+      ],
+    },
+    {
+      code: '<div {{(modifier)}}></div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'The modifier helper should have a string or a variable name containing the modifier name as a first argument.',
+        },
+      ],
+    },
+  ],
+});