Random Redirect: only declare the redirect function when nothing else has

[haqadn]

Proposed changes

• Only declare jetpack_matt_random_redirect() when nothing else already has, so the Random Redirect module no longer fatals on sites where a theme or plugin ships its own copy of the function.

The module was removed from the plugin in 13.6 (#38310) and restored in 16.1 (#50940). While it was gone, some themes started carrying their own copy. A theme's functions.php runs before after_setup_theme, where Jetpack loads module-extras.php, so the theme declares the function first and the plugin's copy hits Cannot redeclare jetpack_matt_random_redirect(). This was reported against 16.1-beta.2 with the panel theme active.

The declaration has to sit inside the conditional rather than behind an early return — PHP binds unconditional top-level function declarations when the file is compiled, so a runtime check placed before one never gets the chance to run.

Reviewing with whitespace hidden (?w=1) shows the real change: 8 added lines. Everything else is the existing function being indented one level.

Related product discussion/links

p1785868165462669-slack-C01U2KGS2PQ

Does this pull request change what data or activity we track or use?

No.

Testing instructions

The redeclare only happens when something else declares the function first, so you need to simulate that.

1. On a test site running this branch, confirm Random Redirect still works normally: visit https://<site>/?random on the front end. You should be redirected to a random published post.

2. Drop this into wp-content/mu-plugins/random-redirect-conflict.php to stand in for a theme that ships its own copy:

   <?php
   function jetpack_matt_random_redirect() {
       wp_die( 'conflicting copy ran' );
   }
   add_action( 'template_redirect', 'jetpack_matt_random_redirect' );

3. Reload any front-end page. On trunk this fatals with Cannot redeclare jetpack_matt_random_redirect(). On this branch the site loads normally.

4. Visit https://<site>/?random again — you should see conflicting copy ran, confirming Jetpack stepped aside and the other copy is the one running.

5. Delete the mu-plugin and confirm /?random goes back to redirecting to a random post.

Note that when another copy wins, the jetpack_random_redirect_enabled filter added in #50940 no longer applies, since that filter lives in Jetpack's implementation. That is the intended trade-off: not fataling matters more than owning the behaviour on those sites.

[github-actions]

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[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the fix/random-redirect-function-conflict branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/random-redirect-function-conflict

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/modules/theme-tools/random-redirect.php	38/51 (74.51%)	-1.49%	1 ❤️‍🩹

Full summary · PHP report · JS report

[chrisbliss18]

The changes look good. Approved.

I added unit test coverage for this issue and other potential issues in Random Redirect in #51041. The unit test finds the issue in the current code and your fix satisfies the test. Please give it a review when you have a chance.

[haqadn]

Cherry-picked to jetpack/branch-16.1 as 265c553 for 16.1-beta.3.