Prevent false positive in redirect_extraneous_paired_endpoint which needlessly redirects (into infinity)

[westonruter]

Summary

The remove_query_arg() function in WordPress is non-idempotent, meaning that if a query var is not present it can still result in a change to the URL (such as converting %20 to +):

wp> remove_query_arg('amp', '/?test=one+two+three')
=> string(20) "/?test=one+two+three"
wp> remove_query_arg('amp', '/?test=one%20two%20three')
=> string(20) "/?test=one+two+three"

This is problematic because redirect_canonical() does the opposite when it re-constructs the URL with parse_str() and rawurlencode_deep(), where rawurlencode_deep() results in spaces being encoded as %20 instead of +.

The result is an infinite redirects between URLs with + and %20 when trying to access a URL with a query string that contains spaces in it.

The fix is to check whether the URL explicitly has the query var before trying to remove it, rather than checking if the URL with the query var removed was changed. This is essentially the same thing that was done before in #5804.

Fixes #6492

Checklist

• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

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[pierlon]

Wow nice find! LGTM .