steefy389 wrote:

Links from index.php do work:
https://commons.wikimedia.org/w/index.php?title=File:Billete_$100_Mexico_Centenario_Reverso.png

• Also applies to inexistant page titles with a $ sign: https://commons.wikimedia.org/wiki/File:Foo_bar_$1_b.jpg
• Only happends when a number follows the $-sign: https://commons.wikimedia.org/wiki/File:Foo_bar_$a_b.jpg
• Doesn't happen locally for me on 1.19-svn
• Might be Wikimedia specific

This was to do with the PathRouter code.

The PathRouter has an extra check to make sure all parameters have been replaced:
For example this:
$router->add( "/wiki/$1", array( 'title' => "$1$2" );
Should never succeed because $2 will never be replaced. It's also just in case there is a situation where it's not a coding error and that is in fact happening because the pattern is not a proper match.

The problem was that it couldn't tell the difference between a $# or $key in the pattern that wasn't replaced and a $1 that came from the url.

I've updated the tests to include some cases I didn't think of originally. And I've fixed the issue by switching to a preg_replace_callback based system.

I bisected it to r104274 which was reverted, then bisected it again to r104689.

reclosing, looks like it was fixed while I was having lunch :-)