Re: [PATCH v2] 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 --patience', they would be shown the diff as expected,
> using the patience algorithm.  '--patience' in this case only changes
> the diff algorithm, but does not cause 'git diff' to show the diff by
> itself.  The diff is shown because that's the default behaviour of
> 'git diff'.
> 
> 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.  So 'git stash show --patience' in the builtin version
> of stash would be completely silent, while it would show the diff in
> the scripted version.
> 
> The same thing would happen for other flags that only affect the way a
> patch is displayed, rather than switching to a different output format
> than the default one.
> 
> Fix this by setting up the default output format for 'git diff'.
> 
> Reported-by: Denton Liu <liu.denton@gmail.com>
> Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
> ---
> 
> Thanks Peff and Junio for your comments on the previous round.
> 
> Compared to v1, this uses the --patience flags for the tests now, and
> mentions only the --patience flag in the commit message.  While the
> original report was about -v, I do agree that --patience is more
> relevant here.
> 
> I think this also deserves some explanation of what didn't change,
> especially after what I said in [*1*].  We're still not using the
> 'diff_opt_parse()' option parser, as it doesn't understand '-v' for
> example.  'setup_revisions()' understands that, but 'diff_opt_parse()'
> doesn't, so we'd still have a change in behaviour at least there.
> After discovering that I gave up on that approach.
> 
> The other thing that was pointed out is the 'diff_setup_done()' call
> here.  'diff_setup_done()' is already called inside of
> 'setup_revisions()', so we don't need to do it again, unless we change
> the output format, which is what we are doing here.  In fact this is
> the same way it's implemented in 'builtin/diff.c'.
> 
> *1*: <20190320214504.GC32487@hank.intra.tgummerer.com>
> 
>  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);
> +	}
>  
>  	rev.diffopt.flags.recursive = 1;
>  	setup_diff_pager(&rev.diffopt);
> diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
> index 97cc71fbaf..83926ab55b 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 --patience ${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" &&
> -- 
> 2.21.0.226.g764ec437b0.dirty
>