add_query_arg changes numerical arguments

[Lex_Robinson]

I noticed this when I used '1=1' as a default query value to prevent a ? being prepended. If an argument passed to add_query_arg is a number, it gets replaced with an incrementing value. It doesn't re-order arguments or parse non-decimal numbers.
I suspect this is being caused by array_merge on line 782 of wp-includes/functions.php

var_dump( add_query_arg( array( 'foo' => 'bar' ), '1=1' ) );
// string '0=1&foo=bar' (length=11)

var_dump( add_query_arg( array( 'a' => 'c' ), '1=1&a=b&10=10' ) );
// string '0=1&a=c&1=10' (length=12)

var_dump( add_query_arg( array( '19' => '19' ), '20=20' ) );
// string '0=20&1=19' (length=9)

var_dump( add_query_arg( array( '3e1' => '3' ), '0x1=1&a=b&010=2' ) );
// string '0x1=1&a=b&010=2&3e1=3' (length=21)

[tyxla]

I was able to reproduce this issue, too.

And @Lex_Robinson, yes, your assumption is correct here - array_merge() flattens the integer indexes. Replacing that array_merge() with array_replace() will do the job, overriding what's necessary from the old query vars, but preserving the query vars with numeric keys.

Patch coming up shortly.

[tyxla]

Fixing the disappearance of numeric keys in add_query_arg(). Including a unit test.

[DrewAPicture]

31306.patch​ still applies, unit tests pass. Moving for commit consideration.

[mordauk]

Patch applies cleanly and tests pass for me.

[wonderboymusic]

In 31966:

Respect numerical keys in add_query_arg(), use array_replace() instead of array_merge().

Adds unit test.

Props tyxla.
Fixes #31306.

[boonebgorges]

array_replace() is PHP 5.3+.

[boonebgorges]

In 31967:

Avoid the use of array_replace() in add_query_arg().

array_replace() was introduced PHP 5.3+. Instead, we walk the array manually.

See [31966].

Fixes #31306.