Subject: Re: [PATCH v3 2/6] notes: replace pseudorefs with real refs

From: David Turner <[email-masked]>
Date: Tue, 28 Jul 2015 15:24:30 -0400

On Tue, 2015-07-28 at 12:00 -0700, Junio C Hamano wrote:
> David Turner <[email-masked]> writes:
> 
> > All-caps files like NOTES_MERGE_REF are pseudorefs, and thus are
> > per-worktree.  We don't want multiple notes merges happening at once
> > (in different worktrees), so we want to make these refs true refs.
> >
> > So, we lowercase NOTES_MERGE_REF and friends.  That way, backends
> > that distinguish between pseudorefs and real refs can correctly
> > handle notes merges.
> >
> > This will also enable us to prevent pseudorefs from being updated by
> > the ref update machinery e.g. git update-ref.
> >
> > Signed-off-by: David Turner <[email-masked]>
> > ---
> 
> This seems to do a bit more than what it claims to do.  As this kind
> of changes are very error-prone to review, I did a bulk replace of
> the three all-caps NOTES_*THING* and compared the result with what
> this patch gives to spot this:
> 
> >  	# Fail to finalize merge
> >  	test_must_fail git notes merge --commit >output 2>&1 &&
> > -	# .git/NOTES_MERGE_* must remain
> > -	test -f .git/NOTES_MERGE_PARTIAL &&
> > -	test -f .git/NOTES_MERGE_REF &&
> > -	test -f .git/NOTES_MERGE_WORKTREE/$commit_sha1 &&
> > -	test -f .git/NOTES_MERGE_WORKTREE/$commit_sha2 &&
> > -	test -f .git/NOTES_MERGE_WORKTREE/$commit_sha3 &&
> > -	test -f .git/NOTES_MERGE_WORKTREE/$commit_sha4 &&
> > +	# .git/notes_merge_* must remain
> > +	git rev-parse --verify notes_merge_partial &&
> > +	git rev-parse --verify notes_merge_ref &&
> > +	test -f .git/notes_merge_worktree/$commit_sha1 &&
> > +	test -f .git/notes_merge_worktree/$commit_sha2 &&
> > +	test -f .git/notes_merge_worktree/$commit_sha3 &&
> > +	test -f .git/notes_merge_worktree/$commit_sha4 &&
> 
> The two "rev-parse --verify" looks semi-sensible [*1*];
> notes_merge_partial is all lowercase and it refers to
> $GIT_DIR/notes_merge_partial, because they are shared across working
> tree. 
> 
> But then why are $GIT_DIR/notes_merge_worktree/* still checked with
> "test -f"?  If they are not refs or ref-like things, why should they
> be downcased?  If they are, why not "rev-parse --verify"?

They are downcased for consistency with the other notes_merge_* stuff.

> [Footnote]
> 
> *1* I say "semi-" sensible, because it looks ugly.  All ref-like
>     things immediately below $GIT_DIR/ are all-caps by convention.
>     Perhaps it is a better idea to move it under refs/; "everything
>     under refs/ is shared across working trees" is probably a much
>     better rule than "all caps but HEAD is special".

Do you mean move all current pseudorefs?  Or just the notes stuff? 

Moving MERGE_HEAD means that if someone upgrades in the middle of a
merge, they'll end up confused.  The same is true of the notes stuff,
but I imagine that many fewer people use notes than use git merge, so I
wasn't going to worry about that.  What do you think?