fix(language_server): treat empty string config path as None in language server

[Copilot]

VS Code's settings UI auto-generates "oxc.configPath": "" when users click the setting field, causing the language server to fail initializing oxlintrc config instead of falling back to .oxlintrc.json.

Changes

• Config path initialization: Match Some("") alongside None to use default config file
• Watcher patterns: Apply same logic when determining file watchers

// Before
let config_path = options.config_path.as_ref().map_or(LINT_CONFIG_FILE, |v| v);

// After  
let config_path = match options.config_path.as_deref() {
    Some("") | None => LINT_CONFIG_FILE,
    Some(v) => v,
};

Applied at both config initialization and watcher pattern registration to ensure consistent behavior.

Original prompt

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This section details on the original issue you should resolve

<issue_title>linter: [vscode] Failed to initialize oxlintrc config</issue_title>
<issue_description>### What version of Oxlint are you using?

1.35.0

What command did you run?

save changes

What does your .oxlintrc.json config file look like?

{
  "plugins": ["typescript", "unicorn", "oxc", "react"],
  "rules": {
    "no-unused-vars": "off",
    "no-unused-expressions": "off",
    "react/jsx-no-undef": "off",
    "react/jsx-no-target-blank": "off",
    "react/exhaustive-deps": "off",
    "react/rules-of-hooks": "error"
  }
}

What happened?

in vscode with settings.json oxc.configPath set to empty string

{
  "oxc.configPath": ""
}

will cause WARN oxc_language_server::linter::server_linter] Failed to initialize oxlintrc config
hence oxc config not recognized.

I looked into the code and found
https://github.com/oxc-project/oxc/blob/oxlint_v1.35.0/crates/oxc_language_server/src/linter/server_linter.rs#L58

empty string is used and not fallback to default .oxlintrc.json, so resulting Failed to initialize oxlintrc config error

but I was not meant to config oxc.configPath to an empty string, it's auto generated by a click on vscode settings UI

Code

https://github.com/oxc-project/oxc/blob/oxlint_v1.35.0/crates/oxc_language_server/src/linter/server_linter.rs#L58

I confirmed the behavior with ChatGPT.

empty string should use default fallback too:

let config_path = match options.config_path.as_deref() {
    Some("") | None => LINT_CONFIG_FILE,
    Some(v) => v,
};

</issue_description>

<agent_instructions>match on Some("") | None in the language server</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes linter: [vscode] Failed to initialize oxlintrc config #17384

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[camc314]

Merge activity

• Dec 28, 1:57 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Dec 28, 2:02 PM UTC: camc314 added this pull request to the Graphite merge queue.
• Dec 28, 2:18 PM UTC: Merged by the Graphite merge queue.

[Copilot]

Pull request overview

This PR fixes an issue where VS Code's settings UI auto-generates an empty string for oxc.configPath when users click on the setting field, causing the language server to fail loading the default .oxlintrc.json config file.

Key changes:

• Modified config path initialization to treat empty strings the same as None, falling back to the default .oxlintrc.json file
• Applied the same logic to file watcher pattern generation for consistency
• Added test coverage to verify empty string config paths behave identically to undefined config paths

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