Extract rule: template-no-unnecessary-curly-parens

README.md

@@ -256,6 +256,7 @@ 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-no-unnecessary-curly-parens](docs/rules/template-no-unnecessary-curly-parens.md)                         | disallow unnecessary parentheses enclosing statements in curlies             |    | 🔧 |    |
 | [template-no-unused-block-params](docs/rules/template-no-unused-block-params.md)                                   | disallow unused block parameters in templates                                |    |    |    |
 | [template-no-valueless-arguments](docs/rules/template-no-valueless-arguments.md)                                   | disallow valueless named arguments                                           |    |    |    |
 | [template-no-whitespace-for-layout](docs/rules/template-no-whitespace-for-layout.md)                               | disallow using whitespace for layout purposes                                |    |    |    |

docs/rules/template-no-unnecessary-curly-parens.md

@@ -0,0 +1,38 @@
+# ember/template-no-unnecessary-curly-parens
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+Disallow unnecessary parentheses enclosing statements in curlies. When invoking a helper with arguments, the outer parentheses around the entire expression are unnecessary.
+
+## Examples
+
+This rule **forbids** the following:
+
+```gjs
+<template>
+  {{(concat "a" "b")}}
+</template>
+```
+
+```gjs
+<template>
+  {{(helper a="b")}}
+</template>
+```
+
+This rule **allows** the following:
+
+```gjs
+<template>
+  {{foo}}
+  {{(foo)}}
+  {{concat "a" "b"}}
+  {{concat (capitalize "foo") "-bar"}}
+</template>
+```
+
+## References
+
+- Ember's [Helper Functions](https://guides.emberjs.com/release/components/helper-functions/) guide

lib/rules/template-no-unnecessary-curly-parens.js

@@ -0,0 +1,64 @@
+function isFixableMustache(node) {
+  // Check if the mustache's "path" is actually a SubExpression with params or hash
+  // e.g., {{(helper arg)}} where the path is (helper arg)
+  return (
+    node.path?.type === 'GlimmerSubExpression' &&
+    ((node.path.params && node.path.params.length > 0) ||
+      (node.path.hash?.pairs && node.path.hash.pairs.length > 0))
+  );
+}
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow unnecessary parentheses enclosing statements in curlies',
+      category: 'Best Practices',
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-unnecessary-curly-parens.md',
+      templateMode: 'both',
+    },
+    fixable: 'code',
+    schema: [],
+    messages: {
+      noUnnecessaryCurlyParens: 'Unnecessary parentheses enclosing statement',
+    },
+    originallyFrom: {
+      name: 'ember-template-lint',
+      rule: 'lib/rules/no-unnecessary-curly-parens.js',
+      docs: 'docs/rule/no-unnecessary-curly-parens.md',
+      tests: 'test/unit/rules/no-unnecessary-curly-parens-test.js',
+    },
+  },
+
+  create(context) {
+    const sourceCode = context.sourceCode || context.getSourceCode();
+
+    return {
+      GlimmerMustacheStatement(node) {
+        if (isFixableMustache(node)) {
+          const subExpr = node.path;
+          context.report({
+            node,
+            messageId: 'noUnnecessaryCurlyParens',
+            fix(fixer) {
+              // Replace {{(helper params hash)}} with {{helper params hash}}
+              const helperName = subExpr.path?.original || '';
+              let replacement = `{{${helperName}`;
+
+              for (const param of subExpr.params || []) {
+                replacement += ` ${sourceCode.getText(param)}`;
+              }
+              for (const pair of subExpr.hash?.pairs || []) {
+                replacement += ` ${sourceCode.getText(pair)}`;
+              }
+              replacement += '}}';
+
+              return fixer.replaceText(node, replacement);
+            },
+          });
+        }
+      },
+    };
+  },
+};

tests/lib/rules/template-no-unnecessary-curly-parens.js

@@ -0,0 +1,78 @@
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const rule = require('../../../lib/rules/template-no-unnecessary-curly-parens');
+const RuleTester = require('eslint').RuleTester;
+
+const validHbs = [
+  '{{foo}}',
+  '{{this.foo}}',
+  '{{(helper)}}',
+  '{{(this.helper)}}',
+  '{{concat "a" "b"}}',
+  '{{concat (capitalize "foo") "-bar"}}',
+];
+
+const invalidHbs = [
+  {
+    code: '<FooBar @x="{{index}}X{{(someHelper foo)}}" />',
+    output: '<FooBar @x="{{index}}X{{someHelper foo}}" />',
+    errors: [{ messageId: 'noUnnecessaryCurlyParens' }],
+  },
+  {
+    code: '<FooBar @x="{{index}}XY{{(someHelper foo)}}" />',
+    output: '<FooBar @x="{{index}}XY{{someHelper foo}}" />',
+    errors: [{ messageId: 'noUnnecessaryCurlyParens' }],
+  },
+  {
+    code: '<FooBar @x="{{index}}--{{(someHelper foo)}}" />',
+    output: '<FooBar @x="{{index}}--{{someHelper foo}}" />',
+    errors: [{ messageId: 'noUnnecessaryCurlyParens' }],
+  },
+  {
+    code: '{{(concat "a" "b")}}',
+    output: '{{concat "a" "b"}}',
+    errors: [{ messageId: 'noUnnecessaryCurlyParens' }],
+  },
+  {
+    code: '{{(helper a="b")}}',
+    output: '{{helper a="b"}}',
+    errors: [{ messageId: 'noUnnecessaryCurlyParens' }],
+  },
+];
+
+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,
+  };
+}
+
+const gjsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+gjsRuleTester.run('template-no-unnecessary-curly-parens', 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-unnecessary-curly-parens', rule, {
+  valid: validHbs,
+  invalid: invalidHbs,
+});