Inconsistent add/get/update/delete_post_meta() functions leads to deleting post metadata.

[jsmoriss]

The add_post_meta(), delete_post_meta(), and update_post_meta() functions all use wp_is_post_revision() to add/delete/update the metadata of the post, not its revision. That's fine, but the get_post_meta() function does NOT use wp_is_post_revision().

As a consequence, if you use get_post_meta() and update_post_meta() during the saving process for a revision, the post metadata ends up being overwritten/deleted: The get_post_meta() function gets the revision metadata, and then the update_post_meta() function updates the post metadata, NOT the revision metadata.

js.

[oglekler]

This needs patch, and I am also wondering if this ticket needs to be handled early.

Trac ticket: https://core.trac.wordpress.org/ticket/58763

## Description
This PR used wp_is_post_revision() function get_post_meta() function.

[oglekler]

Needs testing, I wonder if changes that made for #20564 ticket, are affecting outcome for this issue.

[nicolefurlan]

This ticket could use some testing info to make things easier for testers. @jsmoriss would you be able to add them?

[jsmoriss]

Replying to nicolefurlan:

This ticket could use some testing info to make things easier for testers. @jsmoriss would you be able to add them?

Off the top of my head, here's some code to define a post metadata key for the post (not the revision), then when a revision is restored, the post metadata is erased because get_post_meta() gets the revision metadata (which does not exist) and update_post_meta() updates the post metadata.

add_action( 'save_post', 'test_save_post', 10, 1 );

function test_save_options( $post_id ) {

        $post_type = get_post_type( $post_id );

        if ( 'revision' !== $post_type ) {

                add_post_meta( $post_id, '_test_metadata', 'OK' );      // Adds POST metadata once.

                $val = get_post_meta( $post_id, '_test_metadata', $single = true );     // Value should always be "OK".

                error_log( $post_id . ' ' . $post_type . ' _test_metadata = ' . $val . ' (value should always be "OK" )' );

                if ( empty( $val ) ) {

                        error_log( $post_id . ' ' . $post_type . ' resetting test (by deleting _test_metadata)' );

                        delete_post_meta( $post_id, '_test_metadata' );
                }

        } else {

                $val = get_post_meta( $post_id, '_test_metadata', $single = true ); // Retrieves REVISION metadata (which does not exist).

                update_post_meta( $post_id, '_test_metadata', $val ); // Updates the POST metadata (not the revision metadata).

                error_log( $post_id . ' ' . $post_type . ' _test_metadata = ' . $val . ' (post metadata value now erased)' );
        }
}

The error log output looks something like this:

[09-Oct-2023 19:44:46 UTC] 1086 page _test_metadata = OK (value should always be "OK" )
[09-Oct-2023 19:45:27 UTC] 4624 revision _test_metadata =  (post metadata value now erased)
[09-Oct-2023 19:45:27 UTC] 1086 page _test_metadata =  (value should always be "OK" )
[09-Oct-2023 19:45:27 UTC] 1086 page resetting test (by deleting _test_metadata)

js.

[nicolefurlan]

Wonderful. Thank you @jsmoriss!

This just adds unit tests on top of ​https://github.com/WordPress/wordpress-develop/pull/5216

Trac ticket: https://core.trac.wordpress.org/ticket/58763

[nicolefurlan]

This ticket was discussed in today's bug scrub.

Per @hellofromTonya:

Because of the change is touching older code, a deep dive into the code's commit history is needed. Why? To understand if it's by design, is it the root cause, when did the bug first start.

It would be great to get this into 6.5 Beta 1 to make sure there are no unknowns or side-effects.