feat(eslint): Add ignore pattern for unused vars

Author: TheCodeDestroyer

.changeset/modern-grapes-sit.md

@@ -0,0 +1,5 @@
+---
+'@tcd-devkit/eslint-config': minor
+---
+
+Add more exceptions for id-length rule

.changeset/tidy-zoos-taste.md

@@ -0,0 +1,5 @@
+---
+'@tcd-devkit/eslint-config-ts': minor
+---
+
+Add ignore pattern for unused vars that start with \_

packages/eslint/eslint-config-ts/src/__tests__/rules/no-unused-vars.test.ts

@@ -0,0 +1,70 @@
+import type { Linter } from 'eslint';
+import { config as defineConfig } from 'typescript-eslint';
+import { describe, expect, it } from 'vitest';
+
+import { getLintMessagesForRule } from '@tcd-devkit/internal-utils/test';
+import type { GetLintMessagesOptions } from '@tcd-devkit/internal-utils/test';
+
+import { tsConfig } from '#ts.linter';
+import type { CustomRule } from '#ts.rules';
+
+const safeTsConfig = defineConfig(tsConfig, {
+  languageOptions: {
+    parserOptions: {
+      projectService: true,
+      tsconfigRootDir: process.cwd(),
+    },
+  },
+}) as Linter.Config[];
+
+const ruleId: CustomRule = '@typescript-eslint/no-unused-vars';
+
+const lintTextOptions: GetLintMessagesOptions = {
+  eslintOptions: {
+    cwd: import.meta.dirname,
+  },
+  lintTextOptions: {
+    filePath: './fixtures/fixture.ts',
+  },
+};
+
+describe(`${ruleId} rule`, () => {
+  it('should FAIL when a variable is unused', async () => {
+    const code = `const x = 1;`;
+    const messages = await getLintMessagesForRule(
+      safeTsConfig,
+      code,
+      ruleId,
+      lintTextOptions,
+    );
+
+    expect(messages).toHaveLength(1);
+  });
+
+  it('should PASS when all variables are used', async () => {
+    const code = `
+      const y = 1;
+      console.log(y);
+    `;
+    const messages = await getLintMessagesForRule(
+      safeTsConfig,
+      code,
+      ruleId,
+      lintTextOptions,
+    );
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should PASS for unused variables with ignore pattern', async () => {
+    const code = `const _x = 1;`;
+    const messages = await getLintMessagesForRule(
+      safeTsConfig,
+      code,
+      ruleId,
+      lintTextOptions,
+    );
+
+    expect(messages).toHaveLength(0);
+  });
+});

packages/eslint/eslint-config-ts/src/ts.rules.ts

@@ -6,6 +6,7 @@ export const tsRules = {
   'no-loop-func': ['off'],
   'no-use-before-define': ['off'],
   'no-duplicate-imports': ['off'],
+  '@typescript-eslint/no-unused-vars': ['error', { varsIgnorePattern: '^_' }],
   '@typescript-eslint/consistent-type-imports': ['error'],
   '@typescript-eslint/default-param-last': ['error'],
   '@typescript-eslint/naming-convention': ['off'],