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

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

Thomas Gummerer <t.gummerer@gmail.com> 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.

> 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 <liu.denton@gmail.com>
> Signed-off-by: Thomas Gummerer <t.gummerer@gmail.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);
> +	}

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.

>  	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" &&