Subject: Re: [PATCH] builtin/stash: report failure to write to index

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 6 Feb 2024 06:06:37 +0100

On Mon, Feb 05, 2024 at 11:22:01PM +0100, Rubén Justo wrote:
> On 05-feb-2024 08:01:04, Patrick Steinhardt wrote:
> > The git-stash(1) command needs to write to the index for many of its
> > operations. When the index is locked by a concurrent writer it will thus
> > fail to operate, which is expected. What is not expected though is that
> > we do not print any error message at all in this case. The user can thus
> > easily miss the fact that the command didn't do what they expected it to
> > do and would be left wondering why that is.
> > 
> > Fix this bug and report failures to write to the index. Add tests for
> > the subcommands which hit the respective code paths.
> > 
> > Note that the chosen error message ("Cannot write to the index") does
> > not match our guidelines as it starts with a capitalized letter. This is
> > intentional though and matches the style of all the other messages used
> > in git-stash(1).
> 
> Your message made me curious, so I ran:
> 
>    $ git grep -E '(die|error)\(' builtin/stash.c
>    
>    builtin/stash.c:168:               die(_("'%s' is not a stash-like commit"), revision);
>    builtin/stash.c:214:               return error(_("%s is not a valid reference"), revision);
>    builtin/stash.c:261:               return error(_("git stash clear with arguments is "
>    builtin/stash.c:303:               return error(_("unable to write new index file"));
>    builtin/stash.c:487:                                       die("Failed to move %s to %s\n",
>    builtin/stash.c:523:               die(_("Unable to write index."));
>    builtin/stash.c:544:               return error(_("cannot apply a stash in the middle of a merge"));
>    builtin/stash.c:555:                               return error(_("could not generate diff %s^!."),
>    builtin/stash.c:562:                               return error(_("conflicts in index. "
>    builtin/stash.c:569:                               return error(_("could not save index tree"));
>    builtin/stash.c:610:               ret = error(_("could not write index"));
>    builtin/stash.c:630:               ret = error(_("could not restore untracked files from stash"));
>    builtin/stash.c:702:               return error(_("%s: Could not drop stash entry"),
>    builtin/stash.c:721:               return error(_("'%s' is not a stash reference"), info->revision.buf);
>    builtin/stash.c:872:                       die(_("failed to parse tree"));
>    builtin/stash.c:883:               die(_("failed to unpack trees"));
>    builtin/stash.c:1547:              if (report_path_error(ps_matched, ps)) {
>    builtin/stash.c:1763:                      die("subcommand wasn't specified; 'push' can't be assumed due to unexpected token '%s'",
>    builtin/stash.c:1773:                      die(_("options '%s' and '%s' cannot be used together"), "--pathspec-from-file", "--patch");
>    builtin/stash.c:1776:                      die(_("options '%s' and '%s' cannot be used together"), "--pathspec-from-file", "--staged");
>    builtin/stash.c:1779:                      die(_("'%s' and pathspec arguments cannot be used together"), "--pathspec-from-file");
>    builtin/stash.c:1785:              die(_("the option '%s' requires '%s'"), "--pathspec-file-nul", "--pathspec-from-file");
> 
> Certainly, there are some error messages in builtin/stash.c that do not
> follow the notes in Documentation/CodingGuideLines, but it does not seem
> to be "the style of all other messages" in git-stash.
> 
> However, your message is clear ...  What error messages are you
> considering?

That's because many of the code paths don't use either `error()` or
`die()`, but use `fprintf_ln()` instead:

$ git grep 'fprintf_ln(stderr' -- builtin/stash.c
builtin/stash.c:		fprintf_ln(stderr, _("Too many revisions specified:%s"),
builtin/stash.c:			fprintf_ln(stderr, _("No stash entries found."));
builtin/stash.c:			fprintf_ln(stderr, _("Index was not unstashed."));
builtin/stash.c:		fprintf_ln(stderr, _("No branch name specified"));
builtin/stash.c:			fprintf_ln(stderr, _("Cannot update %s with %s"),
builtin/stash.c:			fprintf_ln(stderr, _("\"git stash store\" requires one "
builtin/stash.c:			fprintf_ln(stderr, _("Cannot update %s with %s"),
builtin/stash.c:			fprintf_ln(stderr, _("No staged changes"));
builtin/stash.c:			fprintf_ln(stderr, _("No changes selected"));
builtin/stash.c:			fprintf_ln(stderr, _("You do not have "
builtin/stash.c:			fprintf_ln(stderr, _("Cannot save the current "
builtin/stash.c:				fprintf_ln(stderr, _("Cannot save "
builtin/stash.c:				fprintf_ln(stderr, _("Cannot save the current "
builtin/stash.c:				fprintf_ln(stderr, _("Cannot save the current "
builtin/stash.c:				fprintf_ln(stderr, _("Cannot save the current "
builtin/stash.c:			fprintf_ln(stderr, _("Cannot record "
builtin/stash.c:		fprintf_ln(stderr, _("Can't use --patch and --include-untracked"
builtin/stash.c:		fprintf_ln(stderr, _("Can't use --staged and --include-untracked"
builtin/stash.c:			fprintf_ln(stderr, _("Did you forget to 'git add'?"));
builtin/stash.c:			fprintf_ln(stderr, _("Cannot initialize stash"));
builtin/stash.c:			fprintf_ln(stderr, _("Cannot save the current status"));
builtin/stash.c:				fprintf_ln(stderr, _("Cannot remove "

Overall, "builtin/stash.c" is a wild mixture of error styles. Some are
likely user-facing, where it might be a good idea to use `fprinf_ln()`
instead of `error()`. But some of them are closer to what we do in this
patch and likely should be converted to use `error()`, too.

I dunno, I find this to be confusing. But I spotted that there's an
instance already where we say `error("cannot write index")`, so I'll
just use that.

Patrick

> > 
> > Reported-by: moti sd <[email-masked]>
> > Signed-off-by: Patrick Steinhardt <[email-masked]>
> > ---
> >  builtin/stash.c  |  6 +++---
> >  t/t3903-stash.sh | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 55 insertions(+), 3 deletions(-)
> > 
> > diff --git a/builtin/stash.c b/builtin/stash.c
> > index b2813c614c..9df072b459 100644
> > --- a/builtin/stash.c
> > +++ b/builtin/stash.c
> > @@ -537,7 +537,7 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
> >  	repo_read_index_preload(the_repository, NULL, 0);
> >  	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET, 0, 0,
> >  					 NULL, NULL, NULL))
> > -		return -1;
> > +		return error(_("Cannot write to the index"));
> >  
> >  	if (write_index_as_tree(&c_tree, &the_index, get_index_file(), 0,
> >  				NULL))
> > @@ -1364,7 +1364,7 @@ static int do_create_stash(const struct pathspec *ps, struct strbuf *stash_msg_b
> >  	repo_read_index_preload(the_repository, NULL, 0);
> >  	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET, 0, 0,
> >  					 NULL, NULL, NULL) < 0) {
> > -		ret = -1;
> > +		ret = error(_("Cannot write to the index"));
> >  		goto done;
> >  	}
> >  
> > @@ -1555,7 +1555,7 @@ static int do_push_stash(const struct pathspec *ps, const char *stash_msg, int q
> >  
> >  	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET, 0, 0,
> >  					 NULL, NULL, NULL)) {
> > -		ret = -1;
> > +		ret = error(_("Cannot write to the index"));
> >  		goto done;
> >  	}
> >  
> > diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
> > index 3319240515..770881e537 100755
> > --- a/t/t3903-stash.sh
> > +++ b/t/t3903-stash.sh
> > @@ -1516,4 +1516,56 @@ test_expect_success 'restore untracked files even when we hit conflicts' '
> >  	)
> >  '
> >  
> > +test_expect_success 'stash create reports a locked index' '
> > +	test_when_finished "rm -rf repo" &&
> > +	git init repo &&
> > +	(
> > +		cd repo &&
> > +		test_commit A A.file &&
> > +		echo change >A.file &&
> > +		touch .git/index.lock &&
> > +
> > +		cat >expect <<-EOF &&
> > +		error: Cannot write to the index
> > +		EOF
> > +		test_must_fail git stash create 2>err &&
> > +		test_cmp expect err
> > +	)
> > +'
> > +
> > +test_expect_success 'stash push reports a locked index' '
> > +	test_when_finished "rm -rf repo" &&
> > +	git init repo &&
> > +	(
> > +		cd repo &&
> > +		test_commit A A.file &&
> > +		echo change >A.file &&
> > +		touch .git/index.lock &&
> > +
> > +		cat >expect <<-EOF &&
> > +		error: Cannot write to the index
> > +		EOF
> > +		test_must_fail git stash push 2>err &&
> > +		test_cmp expect err
> > +	)
> > +'
> > +
> > +test_expect_success 'stash apply reports a locked index' '
> > +	test_when_finished "rm -rf repo" &&
> > +	git init repo &&
> > +	(
> > +		cd repo &&
> > +		test_commit A A.file &&
> > +		echo change >A.file &&
> > +		git stash push &&
> > +		touch .git/index.lock &&
> > +
> > +		cat >expect <<-EOF &&
> > +		error: Cannot write to the index
> > +		EOF
> > +		test_must_fail git stash apply 2>err &&
> > +		test_cmp expect err
> > +	)
> > +'
> > +
> >  test_done
> > -- 
> > 2.43.GIT
> > 
> 
>