Subject: Re: [REGRESSION ps/stash-in-c] git stash show -v

From: Thomas Gummerer <[email-masked]>
Date: Wed, 20 Mar 2019 21:45:04 +0000

On 03/20, Junio C Hamano wrote:
> Thomas Gummerer <[email-masked]> writes:
> 
> > Subject: [PATCH] stash: setup default diff output format if necessary
> >
> > In the scripted 'git stash show' when no arguments are passed, we just
> > pass '--stat' to 'git diff'.  When any argument is passed to 'stash
> > show', we no longer pass '--stat' to 'git diff', and pass whatever
> > flags are passed directly through to 'git diff'.
> >
> > By default 'git diff' shows the patch output.  So when we a user uses
> > 'git stash show -v', they would be shown the diff, because that's the
> > default behaviour of 'git diff', but not actually directly triggered
> > by passing the '-v'.
> >
> > In the C version of 'git stash show', we try to emulate that
> > behaviour using the internal diff API.  However we forgot to set up
> > the default output format, in case it wasn't set by any of the flags
> > that were passed through.
> 
> Well explained.  It might have avoided such a bug if the code did
> not manually stuff the diffopt.* structure fields (instead, e.g.
> prepare an array of strings like {"diff", "--stat", NULL} and let
> the option parser diff_opt_parse() to do its job), but that is
> lamenting over water under the bridge.

I actually think this is still a valid point.  I'm not too familiar
with the diff API, which is why I missed this during my review in the
first place, but I feel like using 'diff_opt_parse()' is still the
right choice here.  Both to fix this bug and to avoid potential
further ones.

Let me give implementing using that a try, I have a feeling like that
might turn out to be better code.

> > So 'git stash show -v' in the builtin
> > version of stash would be completely silent, while it would show the
> > diff before.
> 
> That sounds reasonable.  Thanks for a quick diagnosis and a fix.
> 
> > Fix this by setting up the default output format for 'git diff'.
> >
> > Reported-by: Denton Liu <[email-masked]>
> > Signed-off-by: Thomas Gummerer <[email-masked]>
> > ---
> >  builtin/stash.c  |  4 ++++
> >  t/t3903-stash.sh | 18 ++++++++++++++++++
> >  2 files changed, 22 insertions(+)
> >
> > diff --git a/builtin/stash.c b/builtin/stash.c
> > index 51df092633..012662ce68 100644
> > --- a/builtin/stash.c
> > +++ b/builtin/stash.c
> > @@ -761,6 +761,10 @@ static int show_stash(int argc, const char **argv, const char *prefix)
> >  		free_stash_info(&info);
> >  		usage_with_options(git_stash_show_usage, options);
> >  	}
> > +	if (!rev.diffopt.output_format) {
> > +		rev.diffopt.output_format = DIFF_FORMAT_PATCH;
> > +		diff_setup_done(&rev.diffopt);
> > +	}
> 
> Hmph.  Does this result in setup_done() called twice?  As it would
> indicate another bug in the original code if setup_done() was never
> called, I am assuming that another setup_done() call in the same
> codeflow is already there.

No, it is not called anywhere, will fix that as well in v2.

> >  	rev.diffopt.flags.recursive = 1;
> >  	setup_diff_pager(&rev.diffopt);
> > diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
> > index 97cc71fbaf..e0a50ab267 100755
> > --- a/t/t3903-stash.sh
> > +++ b/t/t3903-stash.sh
> > @@ -612,6 +612,24 @@ test_expect_success 'stash show -p - no stashes on stack, stash-like argument' '
> >  	test_cmp expected actual
> >  '
> >  
> > +test_expect_success 'stash show -v shows diff' '
> > +	git reset --hard &&
> > +	echo foo >>file &&
> > +	STASH_ID=$(git stash create) &&
> > +	git reset --hard &&
> > +	cat >expected <<-EOF &&
> > +	diff --git a/file b/file
> > +	index 7601807..71b52c4 100644
> > +	--- a/file
> > +	+++ b/file
> > +	@@ -1 +1,2 @@
> > +	 baz
> > +	+foo
> > +	EOF
> > +	git stash show -v ${STASH_ID} >actual &&
> > +	test_cmp expected actual
> > +'
> > +
> >  test_expect_success 'drop: fail early if specified stash is not a stash ref' '
> >  	git stash clear &&
> >  	test_when_finished "git reset --hard HEAD && git stash clear" &&