WP_Post::get_instance returns erroneous data for invalid input such as an array or object instead of false.

[deeptiboddapati]

Steps to reproduce the problem:

1. On any wp site which has a post with id =1 run:

$post =  WP_Post::get_instance(array("a","b"));

print_r($post); //will print the post with id = 1 (most probably hello world)

2. It does the same thing with objects

$obj = (object) array("a","b");
$post =  WP_Post::get_instance($obj);
print_r($post);

3. floats it rounds down to the nearest int and tries to get that post

$post =  WP_Post::get_instance(3.5);
returns post with id = 3

4. If you pass in a boolean it returns the first post for true and false for false.

$post =  WP_Post::get_instance(true); //returns post id =1
$post =  WP_Post::get_instance(false); //returns false

[deeptiboddapati]

Test class for WP_Post:get_instance showing where it fails.

[deeptiboddapati]

Adds a line to check if the input param is an int,bool or float and returns false if it isn't.

[swissspidy]

Similar: #33372

[deeptiboddapati]

That ticket was really good to read. It helped me notice that the patch missed numeric strings such as '1' or '1.4'. In that ticket they used is_scalar but that returns true for 'apple' as well as '1'. I used is_numeric in this redone patch since it returns true for '1.36546' or '3' but not for '3rd' or 'apple'.

Additionally negative integers don't seem to be a problem. They return false because the ID field in wp_posts is unsigned and as a result there are no posts with negative IDs. The code handles it the same as it would if there were no post with that number.

[deeptiboddapati]

changed so it accepts numeric strings like '1' or '1.3231'

[deeptiboddapati]

Added coverage for numeric strings in testclass

[boonebgorges]

@deeptiboddapati Thank you for the patch and for the tests!

It seems incorrect to me that 1.4 should be rounded down to 1. That may be how things currently work, but it definitely feels wrong. I assume that backward compatibility will be covered by ensuring that get_post( 1.0 ) does match post 1 (but not get_post( 1.5 ))

[boonebgorges]

In 38381:

Don't improperly cast IDs when fetching post, user, or term objects.

Blindly casting passed IDs to integers can generate false positives
when the ID is cast to 1.

Props deeptiboddapati.
Fixes #37738.

[johnjamesjacoby]

There are reports coming in via Slack that this caused issues with plugins that weren't prepared to correctly handle the newer, quality-controlled return values. After a quick chat, I'm reopening this so we can: revert this to stop that plugin breakage, and look into a better solution in 4.8 or beyond.

[boonebgorges]

In 39992:

Revert to pre-4.7 behavior for fetching object instances by id.

This changeset reverts [38381], which caused inconsistencies in the way the
REST API fetches posts and other objects.

See #38792, #37738.

[boonebgorges]

In 39993:

Revert to pre-4.7 behavior for fetching object instances by id.

This changeset reverts [38381], which caused inconsistencies in the way the
REST API fetches posts and other objects.

Merge of [39992] to the 4.7 branch.

See #38792, #37738.

[boonebgorges]

Making these changes in a backward-compatible way has proved difficult. Let's return to this at some point in the future.