Re: [PATCH 1/3] t/t3430: avoid undocumented git diff behavior
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Jun 9, 2020, 05:18 UTC
- Message-ID
- <xmqqr1uoizqc.fsf@gitster.c.googlers.com>
- In-Reply-To
- <414163bbc3cbdda241bedc7bc4dfb8b493071dcb.1591661021.git.gitgitgadget@gmail.com>
"Chris Torek via GitGitGadget" <gitgitgadget@gmail.com> writes:
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> From: Chris Torek <chris.torek@gmail.com> > > According to the documentation, "git diff" takes at most two commit-ish, > or an A..B style range, or an A...B style symmetric difference range. > The autosquash-and-exec test relied on "git diff HEAD^!", which works > fine for ordinary commits as the revision parse produces two commit-ish, > namely ^HEAD^ and HEAD. > > For merge commits, however, this test makes use of an undocumented > feature:
s/undocumented feature/undefined behaviour/;
The show.sh scripts wants to compute the diff against first parent, and it uses a range notation HEAD^! which happens to mean HEAD^..HEAD for a single parent commit, but it forgets that the commit it may get fed could be a merge. What the code happens to do when given "git diff ^HEAD^2 HEAD^..HEAD" is undefined behaviour and does not even ...
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> the resulting revision parse has all the parents as UNINTERESTING > followed by the HEAD commit. This looks identical to a symmetric > diff parse, which lists the merge bases as UNINTERESTING, followed by > the A (UNINTERESTING) and B revs. So the diff winds up treating it > as one, using the first oid (i.e., HEAD^) and the last (i.e., HEAD). > The documentation, however, says nothing about this usage.
...deserve to be explained in a paragraph like this, I would think.
> Since diff actually just uses HEAD^ and HEAD, call for these directly > here. That makes it possible to improve the diff code's handling of > symmetric difference arguments.
Yes, the resulting code expresses the intent much better.
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> > Signed-off-by: Chris Torek <chris.torek@gmail.com> > --- > t/t3430-rebase-merges.sh | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh > index a1bc3e20016..b454f400ebd 100755 > --- a/t/t3430-rebase-merges.sh > +++ b/t/t3430-rebase-merges.sh > @@ -420,7 +420,7 @@ test_expect_success 'with --autosquash and --exec' ' > git commit --fixup B B.t && > write_script show.sh <<-\EOF && > subject="$(git show -s --format=%s HEAD)" > - content="$(git diff HEAD^! | tail -n 1)" > + content="$(git diff HEAD^ HEAD | tail -n 1)" > echo "$subject: $content" > EOF > test_tick &&