Depends on D19105. Ref T13077. Fixes T12344.
The `[[ ... ]]` syntax accepts and handles characters which would require URL encoding if they appeared in URIs. For example, `[[ 100% Natural Cheese Dust ]]` is a legitimate, supported piece of remarkup syntax, and does not need to be written as `... 100%25 Natural ...`.
Likewise, `[[ BUY $DOGE ]]` is legitimate and does not need to be written as `[[ BUY %24DOGE ]]``. This piece of syntax creates a link to `/w/buy_$doge/`. This may or may not appear in your browser's URL bar as `/w/buy_%24doge/`, but internally "$" is a valid slug character and you'll see `buy_$doge` over Conduit, etc.
However, since users may reasonably copy paths from their browser URL bar, they may have unnecessary URL encoding. The syntax `[[ buy_$doge ]]` is legitimate, but a user copy/pasting may write `[[ buy_%24doge ]]` instead.
Currently, this extra URL encoding causes links to break, since `[[ buy_%24doge ]]` is a treated as link to `/w/buy_24doge/`, just like `[[ Fresh 100%AB Blood ]]` is a link to `/w/fresh_100_ab_blood/`.
To fix this:
- When the target for a link can be URL decoded, try to do lookups on both the un-decoded and decoded variations.
- If the un-decoded variation works, great: use it. This preserves behavior for all existing, working links.
- If the un-decoded variation fails but the decoded variation works, okay: we'll assume you copy-pasted a URL-encoded version and strip URL encoding.
- If both fail, same behavior as before.
Also, use a different spelling for "existent".
See T13084 for some "attacks" based on this behavior. I think the usability affordance this behavior provides greatly outweighs the very mild threat those attacks represent.