commit 421735d8f70b40e470d37d9f76c76319bad029a0
author Gal Paikin <paiking@google.com> Fri Jan 22 10:08:33 2021 +0100
committer Gal Paikin <paiking@google.com> Wed Jan 27 10:17:01 2021 +0000
tree 1d49bfe5fcc47630dbc06224ff6098844df1d2c7
parent e705c894d89c6afbf1e26dc47b71c1e81deba812

Allow posting the same vote on a new patchset

Currently, we don't allow adding a new vote if the exact vote already
exists. This is a reasonable behavior for voting again on the same
patchset, but it is strange across multiple patchsets, example:

1. User votes +2 on Code-Review.
2. Change owner creates a new patchset, and the vote is carried over.
3. User wants to vote +2 again, but can't, as the user already voted.

This should also be fixed in the frontend, as the frontend doesn't allow
clicking "send" at all if there are no changes (and the vote +2 was
carried over).

This bug fix is a blocker for a follow-up feature that would add a
message and new content to the "submitted" email, such that users will
know the diff between the latest approved patchset and the submitted
patchset in case of sticky votes. We allow revoting on a label such that
the "latest approved patchset" will be up to date.

It's better to allow voting on the label even multiple times on the same
patch-set, as this is more correct to adjust the timestamp of the vote
when voting again. This has some side effects:
1. Change message will be posted that the user voted.
2. Email may be different (mentioning the vote as opposed to not
mentioning the vote).
3. Events will fire with the vote (as opposed to fire without the vote).

All of those side effects are okay.

Change-Id: Ide1b122b6ac8788b42c4cc8cdfb486ac8d544375