fix: add type check in add_rest_api_headers to prevent fatal error

[Hsu-Pei-Chun]

Problem

The add_rest_api_headers method assumes $response is always a WP_REST_Response object, but the rest_pre_serve_request filter can pass false in some cases.

This causes a fatal error when WP_DEBUG is enabled or when other plugins trigger warnings that cause "headers already sent":

Fatal error: Uncaught Error: Call to a member function header() on false in wp-content/themes/761-main/functions.php on line 82

Solution

Add an instanceof check before calling the header() method:

public function add_rest_api_headers($response) {
    if ($response instanceof WP_REST_Response) {
        $response->header('X-Robots-Tag', 'noindex, nofollow');
    }
    return $response;
}

This ensures the method only attempts to add headers when $response is a valid WP_REST_Response object.

Summary by CodeRabbit

• Bug Fixes
  • Fixed REST API response header handling to prevent improper header application.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

The add_rest_api_headers function in functions.php now includes a conditional check before setting the X-Robots-Tag header. The header is only applied when the response is an instance of WP_REST_Response, adding type safety to the header modification.

Changes

Cohort / File(s)	Summary
REST API Header Guard functions.php	Added type check in add_rest_api_headers() to conditionally set X-Robots-Tag header only for WP_REST_Response instances instead of unconditionally

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A guard clause stands so tall and true,
Checking types before headers shine through,
Type safety blooms in REST API's domain,
No more unconditional header rain! ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding a type check in add_rest_api_headers to prevent a fatal error when the response is not a WP_REST_Response object.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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