build: set up typescript-eslint

michaelfaith · michaelfaith · commit 32abdfb89e13 · 2025-08-05T05:23:42.000-05:00
This change adds typescript-eslint to our config and fixes a miss in the original TypeScript migration where we weren't linting the newly renamed `ts` files.

This also addresses violations found from both sets of config changes.
diff --git a/eslint.config.ts b/eslint.config.ts
@@ -2,9 +2,9 @@ import path from 'node:path';
 import { fileURLToPath } from 'node:url';
 import js from '@eslint/js';
 import { FlatCompat } from '@eslint/eslintrc';
-import { defineConfig } from 'eslint/config';
 import markdown from 'eslint-plugin-markdown';
 import pluginN from 'eslint-plugin-n';
+import tseslint from 'typescript-eslint';
 import eslintPlugin from './lib/index.js';
 
 const dirname = path.dirname(fileURLToPath(import.meta.url));
@@ -13,14 +13,14 @@ const compat = new FlatCompat({
   recommendedConfig: js.configs.recommended,
 });
 
-export default defineConfig([
+export default tseslint.config([
   // Global ignores
   {
-    ignores: ['node_modules', 'coverage', 'dist'],
+    ignores: ['node_modules', 'coverage', 'dist', 'tests/lib/fixtures'],
   },
   // Global settings
   {
-    languageOptions: { sourceType: 'module' },
+    languageOptions: { parser: tseslint.parser, sourceType: 'module' },
   },
   ...compat.extends(
     'not-an-aardvark/node',
@@ -41,11 +41,18 @@ export default defineConfig([
       'unicorn/no-null': 'off',
       'unicorn/prefer-module': 'off',
       'unicorn/prevent-abbreviations': 'off',
+      'unicorn/no-nested-ternary': 'off',
     },
   },
+  // TypeScript rules
+  tseslint.configs.recommended.map((config) => ({
+    files: ['**/*.ts', '**/*.mts', '**/*.cts'],
+    ...config,
+    rules: { ...config.rules, 'n/no-missing-import': 'off' },
+  })),
   {
     // Apply eslint-plugin rules to our own rules/tests (but not docs).
-    files: ['lib/**/*.js', 'tests/**/*.js'],
+    files: ['lib/**/*.ts', 'tests/**/*.ts'],
     plugins: { 'eslint-plugin': eslintPlugin },
     rules: {
       ...eslintPlugin.configs.all.rules,
@@ -67,7 +74,7 @@ export default defineConfig([
   },
   {
     // Markdown JS code samples in documentation:
-    files: ['**/*.md/*.js'],
+    files: ['**/*.md/*.js', '**/*.md/*.ts'],
     plugins: { markdown },
     linterOptions: { noInlineConfig: true },
     rules: {
diff --git a/lib/index.ts b/lib/index.ts
@@ -41,24 +41,14 @@ import testCaseShorthandStrings from './rules/test-case-shorthand-strings.js';
 
 const require = createRequire(import.meta.url);
 
-const packageMetadata = require("../package.json") as {
-	name: string;
-	version: string;
+const packageMetadata = require('../package.json') as {
+  name: string;
+  version: string;
 };
 
 const PLUGIN_NAME = packageMetadata.name.replace(/^eslint-plugin-/, '');
-const CONFIG_NAMES = [
-  'all',
-  'all-type-checked',
-  'recommended',
-  'rules',
-  'tests',
-  'rules-recommended',
-  'tests-recommended',
-] as const;
-type ConfigName = (typeof CONFIG_NAMES)[number];
 
-const configFilters: Record<ConfigName, (rule: Rule.RuleModule) => boolean> = {
+const configFilters: Record<string, (rule: Rule.RuleModule) => boolean> = {
   all: (rule: Rule.RuleModule) =>
     !(
       rule.meta?.docs &&
@@ -75,7 +65,7 @@ const configFilters: Record<ConfigName, (rule: Rule.RuleModule) => boolean> = {
     configFilters.recommended(rule) && configFilters.tests(rule),
 };
 
-const createConfig = (configName: ConfigName): Linter.Config => ({
+const createConfig = (configName: string): Linter.Config => ({
   name: `${PLUGIN_NAME}/${configName}`,
   plugins: {
     get [PLUGIN_NAME](): ESLint.Plugin {
diff --git a/lib/rules/no-meta-schema-default.ts b/lib/rules/no-meta-schema-default.ts
@@ -83,12 +83,9 @@ const rule: Rule.RuleModule = {
 
           case 'properties': {
             if ('properties' in value && Array.isArray(value.properties)) {
-              for (const property of value.properties) {
-                if (
-                  'value' in property &&
-                  property.value.type === 'ObjectExpression'
-                ) {
-                  checkSchemaElement(property.value);
+              for (const prop of value.properties) {
+                if ('value' in prop && prop.value.type === 'ObjectExpression') {
+                  checkSchemaElement(prop.value);
                 }
               }
             }
diff --git a/lib/rules/no-missing-message-ids.ts b/lib/rules/no-missing-message-ids.ts
@@ -72,7 +72,7 @@ const rule: Rule.RuleModule = {
             collectReportViolationAndSuggestionData(reportInfo);
           for (const messageId of reportMessagesAndDataArray
             .map((obj) => obj.messageId)
-            .filter((messageId) => !!messageId)) {
+            .filter((id) => !!id)) {
             const values =
               messageId.type === 'Literal'
                 ? [messageId]
diff --git a/lib/rules/no-missing-placeholders.ts b/lib/rules/no-missing-placeholders.ts
@@ -111,7 +111,7 @@ const rule: Rule.RuleModule = {
               let match: RegExpExecArray | null;
 
               const messageText: string =
-                // @ts-expect-error
+                // @ts-expect-error -- Property 'value' does not exist on type 'ArrayExpression'.ts(2339)
                 message.value || messageStaticValue.value;
               while ((match = PLACEHOLDER_MATCHER.exec(messageText))) {
                 const matchingProperty =
diff --git a/lib/rules/no-only-tests.ts b/lib/rules/no-only-tests.ts
@@ -56,15 +56,19 @@ const rule: Rule.RuleModule = {
                           sourceCode.getTokenBefore(onlyProperty);
                         const tokenAfter =
                           sourceCode.getTokenAfter(onlyProperty);
-                        if ((tokenBefore && tokenAfter) &&
+                        if (
+                          tokenBefore &&
+                          tokenAfter &&
                           ((isCommaToken(tokenBefore) &&
                             isCommaToken(tokenAfter)) || // In middle of properties
-                          (isOpeningBraceToken(tokenBefore) &&
-                            isCommaToken(tokenAfter))) // At beginning of properties
+                            (isOpeningBraceToken(tokenBefore) &&
+                              isCommaToken(tokenAfter))) // At beginning of properties
                         ) {
                           yield fixer.remove(tokenAfter); // Remove extra comma.
                         }
-                        if ((tokenBefore && tokenAfter) &&
+                        if (
+                          tokenBefore &&
+                          tokenAfter &&
                           isCommaToken(tokenBefore) &&
                           isClosingBraceToken(tokenAfter)
                         ) {
diff --git a/lib/rules/no-unused-message-ids.ts b/lib/rules/no-unused-message-ids.ts
@@ -103,7 +103,7 @@ const rule: Rule.RuleModule = {
             collectReportViolationAndSuggestionData(reportInfo);
           for (const messageId of reportMessagesAndDataArray
             .map((obj) => obj.messageId)
-            .filter((messageId) => !!messageId)) {
+            .filter((id) => !!id)) {
             const values =
               messageId.type === 'Literal'
                 ? [messageId]
diff --git a/lib/rules/no-unused-placeholders.ts b/lib/rules/no-unused-placeholders.ts
@@ -103,7 +103,7 @@ const rule: Rule.RuleModule = {
               data.type === 'ObjectExpression'
             ) {
               const messageValue: string =
-                // @ts-expect-error
+                // @ts-expect-error -- Property 'value' does not exist on type 'SimpleCallExpression'.ts(2339)
                 message.value || messageStaticValue.value;
               // https://github.com/eslint/eslint/blob/2874d75ed8decf363006db25aac2d5f8991bd969/lib/linter.js#L986
               const PLACEHOLDER_MATCHER = /{{\s*([^{}]+?)\s*}}/g;
diff --git a/lib/rules/no-useless-token-range.ts b/lib/rules/no-useless-token-range.ts
@@ -3,14 +3,7 @@
  * @author Teddy Katz
  */
 import type { Rule } from 'eslint';
-import type {
-  CallExpression,
-  Expression,
-  MemberExpression,
-  Node,
-  Property,
-  SpreadElement,
-} from 'estree';
+import type { Expression, MemberExpression, SpreadElement } from 'estree';
 
 import { getKeyName, getSourceCodeIdentifiers } from '../utils.js';
 
diff --git a/lib/rules/require-meta-default-options.ts b/lib/rules/require-meta-default-options.ts
@@ -67,7 +67,7 @@ const rule: Rule.RuleModule = {
     }
 
     if (!metaDefaultOptions) {
-      metaNode &&
+      if (metaNode) {
         context.report({
           node: metaNode,
           messageId: 'missingDefaultOptions',
@@ -78,6 +78,7 @@ const rule: Rule.RuleModule = {
             );
           },
         });
+      }
       return {};
     }
 
@@ -93,7 +94,7 @@ const rule: Rule.RuleModule = {
       schemaProperty.type === 'ObjectExpression' &&
       schemaProperty.properties
         .filter((property) => property.type === 'Property')
-        // @ts-expect-error
+        // @ts-expect-error -- Property 'name' does not exist on type 'ArrayExpression'.ts(2339)
         .find((property) => property.key.name === 'type')?.value.value ===
         'array';
 
diff --git a/lib/rules/require-meta-docs-url.ts b/lib/rules/require-meta-docs-url.ts
@@ -120,7 +120,7 @@ const rule: Rule.RuleModule = {
           // eslint-disable-next-line unicorn/no-negated-condition -- actually more clear like this
           messageId: !urlPropNode
             ? 'missing'
-            : // eslint-disable-next-line unicorn/no-nested-ternary,unicorn/no-negated-condition -- this is fine for now
+            : // eslint-disable-next-line unicorn/no-negated-condition -- this is fine for now
               !expectedUrl
               ? 'wrongType'
               : /* otherwise */ 'mismatch',
diff --git a/lib/rules/require-meta-schema-description.ts b/lib/rules/require-meta-schema-description.ts
@@ -74,7 +74,7 @@ const rule: Rule.RuleModule = {
           continue;
         }
 
-        // @ts-expect-error
+        // @ts-expect-error == Property 'name' does not exist on type 'ClassExpression'.ts(2339)
         switch (key.name ?? key.value) {
           case 'description': {
             hadDescription = true;
diff --git a/lib/rules/test-case-shorthand-strings.ts b/lib/rules/test-case-shorthand-strings.ts
@@ -79,24 +79,29 @@ const rule: Rule.RuleModule = {
 
       let caseInfoFilter: (caseInfo: (typeof caseInfoList)[number]) => boolean;
       switch (shorthandOption) {
-        case 'as-needed':
+        case 'as-needed': {
           caseInfoFilter = (caseInfo) =>
             !caseInfo.shorthand && !caseInfo.needsLongform;
           break;
-        case 'never':
+        }
+        case 'never': {
           caseInfoFilter = (caseInfo) => caseInfo.shorthand;
           break;
-        case 'consistent':
+        }
+        case 'consistent': {
           caseInfoFilter = isConsistent
             ? () => false
             : (caseInfo) => caseInfo.shorthand;
           break;
-        case 'consistent-as-needed':
+        }
+        case 'consistent-as-needed': {
           caseInfoFilter = (caseInfo) =>
             caseInfo.shorthand === hasCaseNeedingLongform;
           break;
-        default:
-          return; // invalid option
+        }
+        default: {
+          return;
+        } // invalid option
       }
 
       caseInfoList.filter(caseInfoFilter).forEach((badCaseInfo) => {
@@ -112,7 +117,7 @@ const rule: Rule.RuleModule = {
               badCaseInfo.node,
               badCaseInfo.shorthand
                 ? `{code: ${sourceCode.getText(badCaseInfo.node)}}`
-                : // @ts-expect-error
+                : // @ts-expect-error -- Property 'properties' does not exist on type 'SimpleLiteral'.ts(2339)
                   sourceCode.getText(badCaseInfo.node.properties[0].value),
             );
           },
diff --git a/lib/utils.ts b/lib/utils.ts
@@ -12,7 +12,6 @@ import type {
   Identifier,
   MaybeNamedClassDeclaration,
   MaybeNamedFunctionDeclaration,
-  MemberExpression,
   ModuleDeclaration,
   Node,
   ObjectExpression,
@@ -359,7 +358,7 @@ function getRuleExportsCJS(
  */
 function findObjectPropertyValueByKeyName(
   obj: ObjectExpression,
-  keyName: String,
+  keyName: string,
 ): Property['value'] | undefined {
   const property = obj.properties.find(
     (prop) =>
diff --git a/package.json b/package.json
@@ -59,8 +59,8 @@
     "@types/estree": "^1.0.8",
     "@types/lodash": "^4.17.18",
     "@types/node": "^20.19.0",
-    "@typescript-eslint/parser": "^8.38.0",
-    "@typescript-eslint/utils": "^8.38.0",
+    "@typescript-eslint/parser": "^8.39.0",
+    "@typescript-eslint/utils": "^8.39.0",
     "@vitest/coverage-istanbul": "^3.2.4",
     "eslint": "^9.31.0",
     "eslint-config-not-an-aardvark": "^2.1.0",
@@ -83,6 +83,7 @@
     "release-it": "^17.2.0",
     "tsup": "^8.5.0",
     "typescript": "^5.9.2",
+    "typescript-eslint": "^8.39.0",
     "vitest": "^3.2.4"
   },
   "peerDependencies": {
diff --git a/tests/lib/rule-setup.ts b/tests/lib/rule-setup.ts
@@ -47,7 +47,7 @@ describe('rule setup is correct', () => {
           const file = readFileSync(filePath, 'utf8');
 
           assert.ok(
-            file.includes("const rule: Rule.RuleModule"),
+            file.includes('const rule: Rule.RuleModule'),
             'is defined as type RuleModule',
           );
         });
@@ -68,7 +68,13 @@ describe('rule setup is correct', () => {
   });
 
   it('should have documentation for all rules', () => {
-    const filePath = path.join(import.meta.dirname, '..', '..', 'docs', 'rules');
+    const filePath = path.join(
+      import.meta.dirname,
+      '..',
+      '..',
+      'docs',
+      'rules',
+    );
     const files = readdirSync(filePath);
 
     assert.deepStrictEqual(
diff --git a/tests/lib/rules/require-meta-type.ts b/tests/lib/rules/require-meta-type.ts
@@ -76,15 +76,13 @@ ruleTester.run('require-meta-type', rule, {
     `,
     'module.exports = {};', // No rule.
     // No `create` function.
-    {
-      code: `
+    `
         const create = {};
         module.exports = {
           meta: {},
           create,
         };
       `,
-    },
   ],
 
   invalid: [
diff --git a/tests/lib/utils.ts b/tests/lib/utils.ts
@@ -36,9 +36,11 @@ type MockRuleInfo = {
     id?: { name: string };
     type: string;
   };
-  meta?: {
-    type: string;
-  } | undefined;
+  meta?:
+    | {
+        type: string;
+      }
+    | undefined;
   isNewStyle: boolean;
 };
 
@@ -1794,9 +1796,7 @@ describe('utils', () => {
       },
       {
         code: `module.exports = { meta: FOO, create(context) {} };`,
-        getResult() {
-          return undefined;
-        }, // returns undefined
+        getResult() {}, // returns undefined
       },
       {
         code: `module.exports = { create(context) {} };`,
diff --git a/types/estree.d.ts b/types/estree.d.ts
@@ -1,4 +1,4 @@
-import { Program as EstreeProgram } from 'estree';
+import type { Expression, Identifier, Node } from 'estree';
 
 /**
  * This file augments the `estree` types to include a couple of types that are not built-in to `estree` that we're using.

Original file line number	Diff line number	Diff line change
`@@ -83,12 +83,9 @@ const rule: Rule.RuleModule = {`
`83`	`83`
`84`	`84`	`case 'properties': {`
`85`	`85`	`if ('properties' in value && Array.isArray(value.properties)) {`
`86`		`- for (const property of value.properties) {`
`87`		`- if (`
`88`		`- 'value' in property &&`
`89`		`- property.value.type === 'ObjectExpression'`
`90`		`- ) {`
`91`		`- checkSchemaElement(property.value);`
	`86`	`+ for (const prop of value.properties) {`
	`87`	`+ if ('value' in prop && prop.value.type === 'ObjectExpression') {`
	`88`	`+ checkSchemaElement(prop.value);`
`92`	`89`	`}`
`93`	`90`	`}`
`94`	`91`	`}`