Merge pull request #2582 from NullVoxPopuli/nvp/template-lint-extract-rule-template-no-unbound

Extract rule: template-no-unbound

Author: NullVoxPopuli

README.md

@@ -340,6 +340,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-attrs-in-components](docs/rules/template-no-attrs-in-components.md)                 | disallow attrs in component templates                     |    |    |    |
 | [template-no-link-to-positional-params](docs/rules/template-no-link-to-positional-params.md)     | disallow positional params in LinkTo component            |    |    |    |
 | [template-no-link-to-tagname](docs/rules/template-no-link-to-tagname.md)                         | disallow tagName attribute on LinkTo component            |    |    |    |
+| [template-no-unbound](docs/rules/template-no-unbound.md)                                         | disallow {{unbound}} helper                               |    |    |    |
 | [template-no-with](docs/rules/template-no-with.md)                                               | disallow {{with}} helper                                  |    |    |    |
 
 ### Ember Data

docs/rules/template-no-unbound.md

@@ -0,0 +1,31 @@
+# ember/template-no-unbound
+
+> **HBS Only**: This rule applies to classic `.hbs` template files only (loose mode). It is not relevant for `gjs`/`gts` files (strict mode), where these patterns cannot occur.
+
+<!-- end auto-generated rule header -->
+
+`{{unbound}}` is a legacy hold over from the days in which Ember's template engine was less performant. Its use today
+is vestigial, and it no longer offers performance benefits.
+
+It is also a poor practice to use it for rendering only the initial value of a property that may later change.
+
+## Examples
+
+This rule **forbids** the following:
+
+```gjs
+<template>
+  {{unbound aVar}}
+</template>
+```
+
+```gjs
+<template>
+  {{some-component foo=(unbound aVar)}}
+</template>
+```
+
+## References
+
+- [deprecations/unbound block syntax](https://deprecations.emberjs.com/v1.x/#toc_block-and-multi-argument-unbound-helper)
+- [Ember api/unbound helper](https://api.emberjs.com/ember/release/classes/Ember.Templates.helpers/methods/each?anchor=unbound)

lib/rules/template-no-unbound.js

@@ -0,0 +1,36 @@
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow {{unbound}} helper',
+      category: 'Deprecations',
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-unbound.md',
+      templateMode: 'loose',
+    },
+    schema: [],
+    messages: { unexpected: 'Unexpected {{unboundHelper}} usage.' },
+    originallyFrom: {
+      name: 'ember-template-lint',
+      rule: 'lib/rules/no-unbound.js',
+      docs: 'docs/rule/no-unbound.md',
+      tests: 'test/unit/rules/no-unbound-test.js',
+    },
+  },
+  create(context) {
+    function check(node) {
+      if (node.path?.type === 'GlimmerPathExpression' && node.path.original === 'unbound') {
+        context.report({
+          node,
+          messageId: 'unexpected',
+          data: { unboundHelper: '{{unbound}}' },
+        });
+      }
+    }
+    return {
+      GlimmerMustacheStatement: check,
+      GlimmerBlockStatement: check,
+      GlimmerSubExpression: check,
+    };
+  },
+};

tests/lib/rules/template-no-unbound.js

@@ -0,0 +1,53 @@
+const rule = require('../../../lib/rules/template-no-unbound');
+const RuleTester = require('eslint').RuleTester;
+
+const validHbs = ['{{foo}}', '{{button}}'];
+
+const invalidHbs = [
+  {
+    code: '{{unbound foo}}',
+    output: null,
+    errors: [{ message: 'Unexpected {{unbound}} usage.' }],
+  },
+  {
+    code: '{{my-thing foo=(unbound foo)}}',
+    output: null,
+    errors: [{ message: 'Unexpected {{unbound}} usage.' }],
+  },
+];
+
+function wrapTemplate(entry) {
+  if (typeof entry === 'string') {
+    return `<template>${entry}</template>`;
+  }
+
+  return {
+    ...entry,
+    code: `<template>${entry.code}</template>`,
+    output: entry.output ? `<template>${entry.output}</template>` : entry.output,
+    errors: entry.errors.map(() => ({ messageId: 'unexpected' })),
+  };
+}
+
+const gjsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+gjsRuleTester.run('template-no-unbound', rule, {
+  valid: validHbs.map(wrapTemplate),
+  invalid: invalidHbs.map(wrapTemplate),
+});
+
+const hbsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser/hbs'),
+  parserOptions: {
+    ecmaVersion: 2022,
+    sourceType: 'module',
+  },
+});
+
+hbsRuleTester.run('template-no-unbound', rule, {
+  valid: validHbs,
+  invalid: invalidHbs,
+});