Prevent theme copies from being uploaded

[poena]

Problem:
Copies of themes that are already in the theme directory gets uploaded by mistake by users who does not know what the theme upload form is for.

We have tried to change the text on the upload page to prevent this, but it is not helping.

Suggested solution:
Even when uploaders change the name of the theme, they usually leave the Theme URI unchanged.

We can compare the Theme URI with existing themes, and stop the upload if the theme URI is a duplicate.
We can also include an exception where the upload can be allowed if the theme author is the same as the uploader.

[dd32]

4039.diff​ is an implementation of this, however..

Blocking this doesn't actually fix the problem, the uploader has most likely already changed the Theme Name (as they were blocked on uploading, and directed them to change it) and is now attempting to upload with a changed Name, but not URI.

All this change will do, is prompt them to change the Theme URI too, and then upload into the review queues with even less data available to say "This is a duplicate".

I'm not against implementing this, but as part of it, I think we need to reconsider the text displayed when it fails the Theme Name in use by another author too.

Ideally, failing either that check, or this check, would display an even firmer "Are you sure you're in the right place?" notice, but I'm not sure on the wording right now.

[dd32]

For reference, the only text displayed on the actual upload screen in the event of a duplicative theme name upload is this:

There is already a theme called Twenty Ten by a different author. Please change the name of your theme in style.css and upload it again.

[joyously]

How about if the text is more explicit: "Duplicates of themes are not allowed in the repository. Are you sure you are in the right place?"

[tellyworth]

Yeah let's try this with text similar to @joyously 's suggestion. Ideally with some kind of stats or logging, so we know how often it happens.

If it still happens often, one option might be a time-out for users who upload a dupe. If they don't already have a published theme, disable the upload form for that user for a few hours.

[poena]

Yes I agree, or "give up" and move the link somewhere else, maybe to the bottom of the page?

[dingo_d]

Can we implement the patch @dd32 suggested but with text that @joyously suggested?

As for the statistics I think this queue gives a good overview of duplicates:

​https://themes.trac.wordpress.org/query?status=closed&resolution=not-approved&col=id&col=summary&col=owner&col=resolution&col=type&col=priority&col=time&desc=1&order=time

[dd32]

In 10431:

Theme Directory: Block duplicate Theme URI's (except when by the current author) and add a "Are you sure you want to upload this here" type message for those who are lost.

Fixes #4039.

[dd32]

In 10432:

Theme Directory: Only use URL rather than URI in the user-facing text.

See r10431.
See #4039.