Fix rest_is_integer validation logic

[coderGtm]

This changeset updates rest_is_integer() to avoid using floating-point conversion when determining whether a value is integer-like.

Previously, the function relied on:

round( (float) $maybe_integer ) === (float) $maybe_integer

This approach breaks for large integers because PHP floating-point values cannot precisely represent all integers above IEEE-754 precision limits (~2^53). As a result, valid large integer values — including values still valid for MySQL/MariaDB BIGINT UNSIGNED columns — could incorrectly fail REST API validation.

The updated implementation:

• avoids float conversion entirely
• validates integer-like values using string pattern matching
• preserves support for signed numeric strings
• rejects decimal and scientific-notation values
• avoids platform integer size limitations (PHP_INT_MAX)

This fixes cases where very large post IDs can cause REST API requests to fail, which may prevent the block editor from loading posts correctly when auto-increment values have been manually increased or otherwise become unusually large.

Trac ticket: https://core.trac.wordpress.org/ticket/65271

Use of AI Tools

AI assistance: Yes
Tool(s): ChatGPT
Model(s): GPT-5.5
Used for: Generating regex pattern

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[westonruter]

This is incorrectly resulting in rest_is_integer( true ) returning true, since (string) true === '1'.

It should return false: https://playground.wordpress.net/php-playground.html#eyJjb2RlIjoiPD9waHBcbnJlcXVpcmUgJy93b3JkcHJlc3Mvd3AtbG9hZC5waHAnO1xuXG52YXJfZHVtcCggcmVzdF9pc19pbnRlZ2VyKCB0cnVlICkgKTsiLCJwaHAiOiI4LjQiLCJ3cCI6IjcuMCJ9

[coderGtm]

Good catch! I fixed it.

[siliconforks]

The problem with this PR is that there's a bunch of cases where it doesn't return the same result as the old implementation.

Here is what the old implementation does:

$ wp eval 'var_dump( rest_is_integer( true ) );'
bool(false)
$ wp eval 'var_dump( rest_is_integer( "123.0" ) );'
bool(true)
$ wp eval 'var_dump( rest_is_integer( "10e-1" ) );'
bool(true)

Here is what the implementation in this PR does:

$ wp eval 'var_dump( rest_is_integer( true ) );'
bool(true)
$ wp eval 'var_dump( rest_is_integer( "123.0" ) );'
bool(false)
$ wp eval 'var_dump( rest_is_integer( "10e-1" ) );'
bool(false)

I don't think we should be trying to rewrite the entire rest_is_integer implementation from scratch - even for a simple function like rest_is_integer, there are a lot of different cases to consider, and there's going to be some risk that the new implemention behaves differently from the original.

My PR (#11893) aims to fix the bug with large integers but otherwise attempts to preserve the existing behavior of the function. I think this is the safest approach.

[coderGtm]

@siliconforks I fixed the boolean case. I am still not sure why would someone need 123.0 or 10e-1 as an integer here, considering its purpose. I'd even go as far as to say that this is an unnoticed bug that slipped under eyeballs for years and must be corrected now.

But even if it is needed, I would still prefer a regex based approach over a float approach. But that could be just me.