Add ESLint language plugin support (#532)

* Initial plan

* Add ESLint language plugin support with YAMLLanguage implementation

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Add changeset for ESLint language plugin support

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Fix getTokensBetween signature for better type consistency

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Update add-language-plugin-support.md

* Add test cases for language plugin support

- Add tests/src/language/directive-comments.ts for ESLint directive comment functionality
- Add tests/src/language/yaml-source-code.ts for YAMLSourceCode class methods
- Tests cover eslint-disable, eslint-enable, eslint-disable-line, eslint-disable-next-line
- Tests cover inline configuration comments
- Tests cover YAMLSourceCode token and comment retrieval methods
- All 45 new tests passing, total 5153 tests pass

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Add token-store and core-rules compatibility tests

- Add tests/src/language/token-store.ts for comprehensive TokenStore testing
- Add tests/src/language/yaml-source-code-with-core-rules.ts for ESLint core rules compatibility
- TokenStore tests cover all methods: getFirstToken, getLastToken, getTokenBefore/After, getTokens, getTokensBetween, getComments
- Core rules test ensures all ESLint built-in rules don't crash with yml/yaml language
- 320 new tests added (28 TokenStore + 292 core rules tests)
- Total: 5,473 tests passing

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Fix linting errors - remove trailing whitespace

Fixed prettier/prettier errors in yaml-source-code.ts test file by removing trailing whitespace from 3 lines.

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Update add-language-plugin-support.md

* Refactor token-store tests to remove getPair helper

Removed getPair helper function and added explicit assertions to each test for navigating the AST structure (ast.body[0], doc.content, content.pairs). This makes tests more explicit and clear about what they're testing, as suggested in code review.

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Add language plugin documentation to README and user guide

Added "Languages" section to both README.md and docs/user-guide/index.md documenting the yml/yaml language identifier and how to use it in ESLint configurations. Follows the same pattern as eslint-plugin-toml documentation.

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Fix test names to accurately reflect single-rule testing

Updated test names in directive-comments.ts:
- Changed "should disable multiple rules separated by commas" to "should disable a specific rule with eslint-disable-next-line"
- Changed "should configure multiple rules in one comment" to "should configure a rule with inline config comment"

These tests only test single rules, so the names now accurately reflect their behavior.

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

* Update tests to actually test multiple rules as originally intended

Restored original test names and updated test implementations:
- "should disable multiple rules separated by commas" now tests disabling both yml/no-empty-key and yml/no-empty-mapping-value with eslint-disable-next-line
- "should configure multiple rules in one comment" now tests configuring both rules in a single inline config comment

Tests now match their descriptions and validate multi-rule directive functionality.

Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ota-meshi <16508807+ota-meshi@users.noreply.github.com>
Co-authored-by: Yosuke Ota <otameshiyo23@gmail.com>

Author: Copilot

.changeset/add-language-plugin-support.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-yml": major
+---
+
+feat: add ESLint language plugin support

README.md

@@ -150,6 +150,31 @@ eslint .
 eslint "src/**/*.{js,yaml,yml}"
 ```
 
+#### Languages
+
+This plugin provides the following language identifiers for use in ESLint configurations:
+
+- `yml/yaml` ... YAML files
+
+For example, to apply settings specifically to YAML files, you can use the `language` field in your ESLint configuration:
+
+```js
+import eslintPluginYml from 'eslint-plugin-yml';
+export default [
+  {
+    files: ["*.yaml", "*.yml", "**/*.yaml", "**/*.yml"],
+    plugins: {
+      yml: eslintPluginYml,
+    },
+    language: "yml/yaml",
+  }
+]
+```
+
+The configuration above is included in the shareable configs provided by this plugin, so using `configs` is generally recommended.
+
+See also <https://eslint.org/docs/latest/use/configure/plugins#specify-a-language>
+
 ## :computer: Editor Integrations
 
 ### Visual Studio Code

docs/user-guide/index.md

@@ -104,6 +104,31 @@ eslint .
 eslint "src/**/*.{js,yaml,yml}"
 ```
 
+#### Languages
+
+This plugin provides the following language identifiers for use in ESLint configurations:
+
+- `yml/yaml` ... YAML files
+
+For example, to apply settings specifically to YAML files, you can use the `language` field in your ESLint configuration:
+
+```js
+import eslintPluginYml from 'eslint-plugin-yml';
+export default [
+  {
+    files: ["*.yaml", "*.yml", "**/*.yaml", "**/*.yml"],
+    plugins: {
+      yml: eslintPluginYml,
+    },
+    language: "yml/yaml",
+  }
+]
+```
+
+The configuration above is included in the shareable configs provided by this plugin, so using `configs` is generally recommended.
+
+See also <https://eslint.org/docs/latest/use/configure/plugins#specify-a-language>
+
 ## :computer: Editor Integrations
 
 ### Visual Studio Code

package.json

@@ -64,6 +64,8 @@
   },
   "homepage": "https://ota-meshi.github.io/eslint-plugin-yml/",
   "dependencies": {
+    "@eslint/core": "^1.0.1",
+    "@eslint/plugin-kit": "^0.5.1",
     "debug": "^4.3.2",
     "diff-sequences": "^27.5.1",
     "escape-string-regexp": "4.0.0",

src/index.ts

@@ -1,21 +1,25 @@
+import type { Linter } from "eslint";
+import type { RuleDefinition } from "@eslint/core";
 import type { RuleModule } from "./types.js";
 import { rules as ruleList } from "./utils/rules.js";
 import base from "./configs/flat/base.js";
 import recommended from "./configs/flat/recommended.js";
 import standard from "./configs/flat/standard.js";
 import prettier from "./configs/flat/prettier.js";
 import * as meta from "./meta.js";
+import type { YAMLSourceCode, YAMLLanguageOptions } from "./language/index.js";
+import { YAMLLanguage } from "./language/index.js";
 
 const configs = {
-  base,
-  recommended,
-  standard,
-  prettier,
+  base: base as Linter.Config[],
+  recommended: recommended as Linter.Config[],
+  standard: standard as Linter.Config[],
+  prettier: prettier as Linter.Config[],
   // Keep flat/* for backward compatibility
-  "flat/base": base,
-  "flat/recommended": recommended,
-  "flat/standard": standard,
-  "flat/prettier": prettier,
+  "flat/base": base as Linter.Config[],
+  "flat/recommended": recommended as Linter.Config[],
+  "flat/standard": standard as Linter.Config[],
+  "flat/prettier": prettier as Linter.Config[],
 };
 
 const rules = ruleList.reduce(
@@ -24,9 +28,12 @@ const rules = ruleList.reduce(
     return obj;
   },
   {} as { [key: string]: RuleModule },
-);
+) as Record<string, RuleDefinition>;
 
-const plugin = { meta, configs, rules };
+const languages = {
+  yaml: new YAMLLanguage(),
+};
 
-export { meta, configs, rules };
-export default plugin;
+export type { YAMLLanguageOptions, YAMLSourceCode };
+export { meta, configs, rules, languages };
+export default { meta, configs, rules, languages };

src/language/index.ts

@@ -0,0 +1,7 @@
+/**
+ * @fileoverview YAML language plugin exports
+ */
+
+export { YAMLLanguage } from "./yaml-language.js";
+export type { YAMLLanguageOptions } from "./yaml-language.js";
+export { YAMLSourceCode } from "./yaml-source-code.js";