commit 1063e30c58575c1a47dfa18418cb8e8cb4bf02cf
author Jonathan Nieder <jrn@google.com> Tue Apr 02 22:29:31 2019 -0700
committer Jonathan Nieder <jrn@google.com> Tue Apr 02 22:51:38 2019 -0700
tree 6062716d65b3ec280ab3a863b817797b5314ed6c
parent 1a4b6382da011031fa0a76ea3217f0244307daae

Reject changes with Change-Id above footer

Documentation/user-change-id.txt explains:

	To be picked up by Gerrit, a Change-Id line must be in the
	footer (last paragraph) of a commit message, and may be mixed
	together with Signed-off-by, Acked-by, or other such lines.

It is easy to forget to do that, producing a commit message like

	Do something great

	Change-Id: I55ca6286e3e4f4fba5d0448333fa99fc5a404a73

	Bug: 12345

Because of the blank line between the Change-Id and other trailer
line, the Change-Id is not picked up by Gerrit.  Worse, if the
repository is configured with "Require Change-Id in commit message"
set to false, then Gerrit comes up with its own change-id for the
change.  If I amend my commit in response to review comments and push
for review again, Gerrit comes up with another change-id, so my
amended version of the change shows up as a new change.

This sequence of events can be avoided by setting "Require Change-Id"
to true, but some projects like to review changes from upstreams that
don't use Gerrit.  Fortunately, even these projects don't need changes
with a Change-Id before the footer.  Treat them as an error
unconditionally, with the same advice to the user about how to clean up
that is already shown in Require Change-Id mode:

	ERROR: Change-Id must be in message footer

	Hint: run
	  git commit --amend
	and move 'Change-Id: Ixxx..' to the bottom on a separate line

As a side benefit, treating this as its own error type also allows
simplifying the error reporting for changes with no Change-Id.

Reported-by: Paul Crowley <paulcrowley@google.com>
Change-Id: Ia5d43370e075d6fc13cd9b22031436f1138e90c0