fix(linter/plugins): Return empty object for unimplemented parserServices (#15364)

## Summary

- Changed `sourceCode.parserServices` from throwing an error to
returning an empty object `{}`
- Aligns with ESLint specification for parsers that don't implement
parser services
- Prevents crashes in ESLint plugins such as
`eslint-plugin-better-tailwindcss`.

## Motivation

According to the [ESLint custom parser
documentation](https://eslint.org/docs/latest/extend/custom-parsers#parseforeslint-return-object):

> services can contain any parser-dependent services (such as type
checkers for nodes). The value of the services property is available to
rules as context.sourceCode.parserServices. **Default is an empty
object.**

The current implementation throws an error when `parserServices` is
accessed, which breaks plugins that use defensive checks like:

```typescript
if(typeof ctx.sourceCode.parserServices?.defineTemplateBodyVisitor === "function"){
  // ...
}
```

Plugin authors defensively handle:
- ✅ `parserServices` being undefined
- ✅ `defineTemplateBodyVisitor` not existing
- ❌ `parserServices` getter throwing an error (unexpected)

## Solution

Return an empty object `{}` for unimplemented parser services, which:
1. Matches ESLint's documented default behavior
2. Allows plugins' defensive checks to work correctly
3. Provides correct semantics for "not implemented"

## Test Plan

- Existing tests should continue to pass
- Plugins using defensive checks like the example above will no longer
crash

## Related

Fixes the compatibility issue with plugins like
[eslint-plugin-better-tailwindcss](https://github.com/schoero/eslint-plugin-better-tailwindcss/blob/a90cc3f547098a4293d7b0b7998bf6774f717cd2/src/utils/rule.ts#L140)

---------

Signed-off-by: magic-akari <akari.ccino@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: overlookmotel <theoverlookmotel@gmail.com>

Author: 3 people

apps/oxlint/src-js/plugins/source_code.ts

@@ -127,7 +127,7 @@ export const SOURCE_CODE = Object.freeze({
 
   // Get parser services for the file.
   get parserServices(): { [key: string]: unknown } {
-    throw new Error('`sourceCode.parserServices` not implemented yet'); // TODO
+    return {}; // TODO
   },
 
   // Get source text as array of lines, split according to specification's definition of line breaks.

apps/oxlint/test/e2e.test.ts

@@ -254,4 +254,8 @@ describe('oxlint CLI', () => {
   it('should support UTF16 characters in source code and comments with correct spans', async () => {
     await testFixture('unicode-comments');
   });
+
+  it('should return empty object for `parserServices` without throwing', async () => {
+    await testFixture('parser_services');
+  });
 });

apps/oxlint/test/fixtures/parser_services/.oxlintrc.json

@@ -0,0 +1,9 @@
+{
+  "jsPlugins": ["./plugin.ts"],
+  "categories": {
+    "correctness": "off"
+  },
+  "rules": {
+    "parser-services-plugin/check-parser-services": "error"
+  }
+}

apps/oxlint/test/fixtures/parser_services/files/index.js

@@ -0,0 +1,2 @@
+// Simple file to test parserServices access
+console.log('testing parserServices');

apps/oxlint/test/fixtures/parser_services/output.snap.md

@@ -0,0 +1,21 @@
+# Exit code
+1
+
+# stdout
+```
+  x parser-services-plugin(check-parser-services): typeof context.sourceCode.parserServices: object
+   ,-[files/index.js:1:1]
+ 1 | // Simple file to test parserServices access
+   : ^
+ 2 | console.log('testing parserServices');
+   `----
+
+Found 0 warnings and 1 error.
+Finished in Xms on 1 file using X threads.
+```
+
+# stderr
+```
+WARNING: JS plugins are experimental and not subject to semver.
+Breaking changes are possible while JS plugins support is under development.
+```

apps/oxlint/test/fixtures/parser_services/plugin.ts

@@ -0,0 +1,31 @@
+import type { Plugin, Node } from '../../../dist/index.js';
+
+const SPAN: Node = {
+  start: 0,
+  end: 0,
+  range: [0, 0],
+  loc: {
+    start: { line: 0, column: 0 },
+    end: { line: 0, column: 0 },
+  },
+};
+
+const plugin: Plugin = {
+  meta: {
+    name: 'parser-services-plugin',
+  },
+  rules: {
+    'check-parser-services': {
+      create(context) {
+        context.report({
+          message: `typeof context.sourceCode.parserServices: ${typeof context.sourceCode.parserServices}`,
+          node: SPAN,
+        });
+
+        return {};
+      },
+    },
+  },
+};
+
+export default plugin;