Extract rule: template-no-inline-styles

README.md

@@ -203,6 +203,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-chained-this](docs/rules/template-no-chained-this.md)                                     | disallow redundant `this.this` in templates                     |    | 🔧 |    |
 | [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-inline-styles](docs/rules/template-no-inline-styles.md)                                   | disallow inline styles                                          |    |    |    |
 | [template-no-input-placeholder](docs/rules/template-no-input-placeholder.md)                           | disallow placeholder attribute on input elements                |    |    |    |
 | [template-no-input-tagname](docs/rules/template-no-input-tagname.md)                                   | disallow tagName attribute on {{input}} helper                  |    |    |    |
 | [template-no-log](docs/rules/template-no-log.md)                                                       | disallow {{log}} in templates                                   |    |    |    |

docs/rules/template-no-inline-styles.md

@@ -0,0 +1,40 @@
+# ember/template-no-inline-styles
+
+<!-- end auto-generated rule header -->
+
+Inline styles are not the best practice because they are hard to maintain and usually make the overall size of the project bigger. This rule forbids inline styles. Use CSS classes instead.
+
+## Examples
+
+This rule **forbids** the following:
+
+```gjs
+<template><div style='width:900px'></div></template>
+```
+
+This rule **allows** the following:
+
+```gjs
+<template><div class='wide-element'></div></template>
+```
+
+```gjs
+<template>
+  {{! allowed when `allowDynamicStyles` is enabled  }}
+  <div style={{html-safe (concat 'background-image: url(' url ')')}}></div>
+</template>
+```
+
+## Options
+
+| Name                 | Type      | Default | Description                                                                           |
+| -------------------- | --------- | ------- | ------------------------------------------------------------------------------------- |
+| `allowDynamicStyles` | `boolean` | `true`  | When `true`, allows dynamic style values (e.g. `style={{...}}` or `style="{{...}}"`). |
+
+## Related Rules
+
+- [style-concatenation](style-concatenation.md)
+
+## References
+
+- [Deprecations/binding style attributes](https://emberjs.com/deprecations/v1.x/#toc_binding-style-attributes)

lib/rules/template-no-inline-styles.js

@@ -0,0 +1,47 @@
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow inline styles',
+      category: 'Best Practices',
+      recommendedGjs: false,
+      recommendedGts: false,
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-inline-styles.md',
+    },
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          allowDynamicStyles: { type: 'boolean' },
+        },
+        additionalProperties: false,
+      },
+    ],
+    messages: { noInlineStyles: 'Inline styles are not allowed' },
+  },
+  create(context) {
+    const options = context.options[0] || {};
+    const allowDynamicStyles =
+      options.allowDynamicStyles === undefined ? true : options.allowDynamicStyles;
+
+    return {
+      GlimmerElementNode(node) {
+        const styleAttr = node.attributes?.find((a) => a.name === 'style');
+        if (!styleAttr) {
+          return;
+        }
+
+        // If allowDynamicStyles is true, skip dynamic style values (MustacheStatement/ConcatStatement)
+        if (allowDynamicStyles) {
+          const valType = styleAttr.value?.type;
+          if (valType === 'GlimmerMustacheStatement' || valType === 'GlimmerConcatStatement') {
+            return;
+          }
+        }
+
+        context.report({ node: styleAttr, messageId: 'noInlineStyles' });
+      },
+    };
+  },
+};

tests/lib/rules/template-no-inline-styles.js

@@ -0,0 +1,25 @@
+const rule = require('../../../lib/rules/template-no-inline-styles');
+const RuleTester = require('eslint').RuleTester;
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+ruleTester.run('template-no-inline-styles', rule, {
+  valid: [
+    '<template><div class="foo"></div></template>',
+    // Test cases ported from ember-template-lint
+    '<template><div></div></template>',
+    '<template><span></span></template>',
+    '<template><ul class="dummy"></ul></template>',
+    '<template><div style={{foo}}></div></template>',
+    '<template><div style={{html-safe (concat "background-image: url(" url ")")}}></div></template>',
+  ],
+  invalid: [
+    {
+      code: '<template><div style="color: red"></div></template>',
+      output: null,
+      errors: [{ messageId: 'noInlineStyles' }],
+    },
+  ],
+});