Remove "Attached To" column from the attachments table

[scribu]

Before 3.5, an attachment's parent post meant "this is the post this file belongs to; it will automatically show up in the gallery". In 3.5, if it's even set, it means "this is the post this file was originally uploaded to".

After just ​seeing a user trying to insert an image into a post using the "Attached To" column (around 2:30), I'm thinking maybe we should hide that column.

[scribu]

The first patch just removes the column registration; the second removes the column implementation as well (the JS logic still remains).

[mdgl]

See also #22085. It seems we need to think more carefully about what we're doing here.

Changing the gallery shortcode to rely only on a list of IDs is fine for posts created in 3.5 or later, but for existing posts we still need to be able to find gallery images by searching for attachment children. There is also the issue of pretty permalinks for these attached children, which appear as though they "belong" to the parent post.

Attachments also don't need to be either images or in a gallery and many sites/themes may be relying on grouping such content together through the post_parent field and use of APIs such as {wp_}get_attachment_link(), {next/previous/adjacent}_image_link and so on.

So if you are trying to preserve some kind of backwards compatibility in 3.5 I suspect the post that an attachment is, erm, "attached" to is still of interest/concern to users.

Finally, don't forget #21391 kinda promised some kind of support for reparenting attachments.

[nacin]

I'd like to leave this for 3.5, but rename it to "Uploaded to".

[helenyhou]

Replying to mdgl:

Finally, don't forget #21391 kinda promised some kind of support for reparenting attachments.

#21391 says

We can get a lot of things "for free" if we move it to be a proper post type UI, including: ... Re-parenting (even if only exposed by a plugin)

[helenyhou]

22439.3.diff​ to just rename it. I think it's better to retain the column for 3.5 - de-emphasizing doesn't necessarily warrant its removal right now.

Semi-related: #20164 to make that attach-to-something box better, which I guess would also disappear if the column did.

[nacin]

In 22630:

Media Library list table: Rename 'Attached to' to 'Uploaded to'.

In 3.5, we have chosen to de-emphasize the "attaching" part of the
post-attachment relationship. Existing functionality remains the same,
but UI emphasis is now placed on "parent" being where the item was
originally uploaded.

fixes #22439.