Re: [PATCH 1/5] rebase -r: demonstrate bug with conflicting merges

[Junio C Hamano <gitster@pobox.com>]

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> When calling `merge` on a branch that has already been merged, that
> `merge` is skipped quietly, but currently a MERGE_HEAD file is being
> left behind and will then be grabbed by the next `pick` (that did
> not want to create a *merge* commit).
>
> Demonstrate this.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  t/t3430-rebase-merges.sh | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)

For a trivially small change/fix like this, it is OK and even
preferrable to make 1+2 a single step, as applying t/ part only to
try to see the breakage (or "am"ing everything and then "diff |
apply -R" the part outside t/ for the same purpose) is easy enough.

Because the patch 2 with your method ends up showing only the test
set-up part in the context by changing _failure to _success, without
showing what end-user visible breakage the step fixed, which usually
comes near the end of the added test piece.  A single patch that
gives tests that ought to succeed would not force the readers to
switch between patches 1 and 2 while reading the fix.

Of course, the above would not apply for a more involved case where
the actual fix to the code needs to span multiple patches.

Thanks.

> diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
> index aa7bfc88ec..1f08a33687 100755
> --- a/t/t3430-rebase-merges.sh
> +++ b/t/t3430-rebase-merges.sh
> @@ -396,4 +396,20 @@ test_expect_success 'with --autosquash and --exec' '
>  	grep "G: +G" actual
>  '
>  
> +test_expect_failure '--continue after resolving conflicts after a merge' '
> +	git checkout -b already-has-g E &&
> +	git cherry-pick E..G &&
> +	test_commit H2 &&
> +
> +	git checkout -b conflicts-in-merge H &&
> +	test_commit H2 H2.t conflicts H2-conflict &&
> +	test_must_fail git rebase -r already-has-g &&
> +	grep conflicts H2.t &&

Is this making sure that the above test_must_fail succeeded because
of a conflict and not due to any other failure?  I would have used
"ls-files -u H2.t" to see if the index is unmerged, which probably
is a more direct way to test what this is trying to test, but if we
are in the conflicted state, the one side of << == >> has this
string (the other has "H2" in it, presumably?), so in practice this
should be good enough.

> +	echo resolved >H2.t &&
> +	git add -u &&

and we resolve to continue.

> +	git rebase --continue &&
> +	test_must_fail git rev-parse --verify HEAD^2 &&

Even if we made an octopus by mistake, the above will catch it,
which is good.

> +	test_path_is_missing .git/MERGE_HEAD
> +'
> +
>  test_done

And from the proposed log message, I am reading that the last two
things (i.e. resulting tip is a child with a single parent and there
is no leftover MERGE_HEAD file) fail without the fix.  

This is enough material to convince me or anybody that the bug is
worth fixing.  Thanks for being careful noticing a glitch during
your real (and otherwise unrelated to the bug) work and following
through.