[PATCH] am: handle stray $dotest directory case

[PATCH] am: handle stray $dotest directory case

[Ramkumar Ramachandra]

The following bug has been observed since rr/rebase-autostash:

  $ git am  # no input file
  ^C
  $ git am --abort
  Resolve operation not in progress, we are not resuming.

This happens because the following test fails:

  test -d "$dotest" && test -f "$dotest/last" && test -f "$dotest/next"

and am precludes the possibility of a stray $dotest directory
existing (when $dotest/{last,next} are not present).

Fix the bug by checking for a stray $dotest directory explicitly and
removing it on --abort.

Reported-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 git-am.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/git-am.sh b/git-am.sh
index 1cf3d1d..f46a123 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -506,6 +506,11 @@ then
 	esac
 	rm -f "$dotest/dirtyindex"
 else
+	# Possible stray $dotest directory
+	if test -d "$dotest" && test t = "$abort"; then
+		clean_abort
+	fi
+
 	# Make sure we are not given --skip, --resolved, nor --abort
 	test "$skip$resolved$abort" = "" ||
 		die "$(gettext "Resolve operation not in progress, we are not resuming.")"
-- 
1.8.3.1.379.ged35616

Re: [PATCH] am: handle stray $dotest directory case

[Junio C Hamano]

Ramkumar Ramachandra <artagnon@gmail.com> writes:

> The following bug has been observed since rr/rebase-autostash:
>
>   $ git am  # no input file
>   ^C
>   $ git am --abort
>   Resolve operation not in progress, we are not resuming.
>
> This happens because the following test fails:
>
>   test -d "$dotest" && test -f "$dotest/last" && test -f "$dotest/next"
>
> and am precludes the possibility of a stray $dotest directory
> existing (when $dotest/{last,next} are not present).

Why did the original code sequence that read:

	if test -d "$dotest"
        then
		... handle skip, resolved, abort, because
                ... these can be run ONLY when we know we have
                ... started an "am" session.
		... catch new "git am mbox" invocation and error
                ... out, because that should not be allowed when
                ... we know we have started an "am" session.

had to change its guarding condition to

	if test -d "$dotest" && test -f "$dotest/last" && test -f "$dotest/next"

in the first place?  Perhaps _that_ guarding condition is what needs
to be fixed, by reverting it back to just "does $dotest exist?"

Adding a single case workaround smells like a band-aid to me.

> Fix the bug by checking for a stray $dotest directory explicitly and
> removing it on --abort.
>
> Reported-by: Junio C Hamano <gitster@pobox.com>
> Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
> ---
>  git-am.sh | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/git-am.sh b/git-am.sh
> index 1cf3d1d..f46a123 100755
> --- a/git-am.sh
> +++ b/git-am.sh
> @@ -506,6 +506,11 @@ then
>  	esac
>  	rm -f "$dotest/dirtyindex"
>  else
> +	# Possible stray $dotest directory
> +	if test -d "$dotest" && test t = "$abort"; then
> +		clean_abort
> +	fi
> +
>  	# Make sure we are not given --skip, --resolved, nor --abort
>  	test "$skip$resolved$abort" = "" ||
>  		die "$(gettext "Resolve operation not in progress, we are not resuming.")"

Re: [PATCH] am: handle stray $dotest directory case

[Ramkumar Ramachandra]

Junio C Hamano wrote:
> Perhaps _that_ guarding condition is what needs
> to be fixed, by reverting it back to just "does $dotest exist?"
>
> Adding a single case workaround smells like a band-aid to me.

Like I pointed out earlier, the original codepath is not equipped to
handle this case.  A "normal" git am --abort runs:

  git read-tree --reset -u HEAD ORIG_HEAD
  git reset ORIG_HEAD

blowing away the top commit in the scenario you outlined.

This happens because that codepath incorrectly believes that an am is
"in progress".  What this means is that it believes that some of the
am code actually got executed in the previous run, setting ORIG_HEAD
etc.  In your scenario

  % git am
  ^C

nothing is executed, and a stray directory is left behind.

If anything, I think the check for $dotest/{next,last} has made the
code more robust by correctly verifying that some code did get
executed, and that an am is indeed in progress.  The bug you have
outlined is equivalent to:

  % mkdir .git/rebase-apply
  % git am --abort

Therefore, the fix is to treat it as exactly that: a stray directory
that needs to be cleaned up in the codepath that treats it as a "fresh
run"; not going through the "normal" am --abort logic and blowing away
the top commit.

Makes sense?

Re: [PATCH] am: handle stray $dotest directory case

[Junio C Hamano]

Ramkumar Ramachandra <artagnon@gmail.com> writes:

> Junio C Hamano wrote:
>> Perhaps _that_ guarding condition is what needs
>> to be fixed, by reverting it back to just "does $dotest exist?"
>>
>> Adding a single case workaround smells like a band-aid to me.
>
> Like I pointed out earlier, the original codepath is not equipped to
> handle this case.  A "normal" git am --abort runs:
>
>   git read-tree --reset -u HEAD ORIG_HEAD
>   git reset ORIG_HEAD

Hmph, when did ORIG_HEAD set, and what commit does it point at?

As "git am" reading from stdin, waiting, hasn't moved HEAD yet at
all, I think two things need to happen to fix that:

 (1) at around the call to check_patch_format and split_patches,
     clear ORIG_HEAD (this may have to be done only !$rebasing,
     though).

 (2) safe_to_abort() should make sure ORIG_HEAD exists; otherwise it
     is unsafe.

But that is entirely an independent issue (I am going to agree with
you in the end).

> blowing away the top commit in the scenario you outlined.
>
> This happens because that codepath incorrectly believes that an am is
> "in progress".  What this means is that it believes that some of the
> am code actually got executed in the previous run, setting ORIG_HEAD
> etc.  In your scenario
>
>   % git am
>   ^C
>
> nothing is executed, and a stray directory is left behind.

That is a correct observation.  But it needed a bit of thinking to
reach your conclusion that special casing this and handling --abort
in a new different codepath is the right solution.

> If anything, I think the check for $dotest/{next,last} has made the
> code more robust by correctly verifying that some code did get
> executed, and that an am is indeed in progress.  The bug you have
> outlined is equivalent to:
>
>   % mkdir .git/rebase-apply
>   % git am --abort

Yes.  Or a previous "git am" run lost "$dotest/last" by a bug and
then the user asked to "am --abort".  Either case, the best you can
do is probably to blow away .git/rebase-apply directory.

How would "am --skip", "am --resolved", or "am anothermbox" behave
in this "we already have $dotest because the user started one
session but killed it" case, which used to be covered by -d $dotest
alone but now flows to the other side of the if/else/fi codepath?
Do they need a similar treatment, or would they naturally error out
as they should?

Re: [PATCH] am: handle stray $dotest directory case

[Ramkumar Ramachandra]

Junio C Hamano wrote:
> Hmph, when did ORIG_HEAD set, and what commit does it point at?

By some unrelated previous operation (eg. pull, rebase, merge).  The
point is that at any point in "normal operation", ORIG_HEAD exists,
and usually points to @~N, for some N.  If I rm .git/ORIG_HEAD by
hand, the am --abort obviously errors out:

  $ git am --abort
  fatal: Not a valid object name ORIG_HEAD
  fatal: ambiguous argument 'ORIG_HEAD': unknown revision or path not
in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'

> As "git am" reading from stdin, waiting, hasn't moved HEAD yet at
> all, I think two things need to happen to fix that:
>
>  (1) at around the call to check_patch_format and split_patches,
>      clear ORIG_HEAD (this may have to be done only !$rebasing,
>      though).
>
>  (2) safe_to_abort() should make sure ORIG_HEAD exists; otherwise it
>      is unsafe.
>
> But that is entirely an independent issue (I am going to agree with
> you in the end).

Exactly.  It might be nice to fix those two things (are there any
observed bugs?), but it is entirely orthogonal to our issue.

> That is a correct observation.  But it needed a bit of thinking to
> reach your conclusion that special casing this and handling --abort
> in a new different codepath is the right solution.

Yeah, the commit message is lacking.

> How would "am --skip", "am --resolved", or "am anothermbox" behave
> in this "we already have $dotest because the user started one
> session but killed it" case, which used to be covered by -d $dotest
> alone but now flows to the other side of the if/else/fi codepath?
> Do they need a similar treatment, or would they naturally error out
> as they should?

am --skip and am --resolved will error out, saying "Resolve operation
not in progress, we are not resuming".  The message needs to be
tweaked.

am anothermbox will work just fine, implicitly overwriting the
existing $dotest directory.  But yeah, we could explicitly remove the
directory and allow the mkdir -p to re-create it.

I'll probably work on these follow-ups in the morning.  Thanks for poking.

Re: [PATCH] am: handle stray $dotest directory case

[Junio C Hamano]

Ramkumar Ramachandra <artagnon@gmail.com> writes:

>> But that is entirely an independent issue (I am going to agree with
>> you in the end).
>
> Exactly.  It might be nice to fix those two things (are there any
> observed bugs?), but it is entirely orthogonal to our issue.

OK.

>> That is a correct observation.  But it needed a bit of thinking to
>> reach your conclusion that special casing this and handling --abort
>> in a new different codepath is the right solution.
>
> Yeah, the commit message is lacking.

OK.  I'll queue this on 'pu', not in 'next' so that it can be
rerolled.

> I'll probably work on these follow-ups in the morning.  Thanks for poking.

Thanks.