git bug

> Dear Git Team,
> 
> I am writing to report a potential bug encountered while using the "git
> stash" command. The issue was observed during a troubleshooting. Please
> find the details below:
> 
> *Problem Description:*
> 
> The "git stash" command is not providing any feedback or indication of
> execution, even though modifications are present and the stash operation is
> attempted.
> *Steps to Reproduce:*
> 
> Make modifications to a file.
> Execute "git stash" to stash changes.
> *Expected Behavior:*
> 
> The "git stash" command should provide feedback on the stash operation,
> confirming whether it was successful or if there were any errors.
> *Additional Information:*
> The issue was initially observed when executing "git commit -a --amend" and
> pressing Ctrl+Z to exit. Subsequent attempts to use "git stash" resulted in
> an error.
> Testing with a provided ZIP file containing a problematic repository
> confirmed the issue's recurrence.
> *Investigation and Findings:*
> 
> Upon investigation, it was discovered that the use of Ctrl+Z after "git
> commit -a --amend" might be the root cause.
> Deleting a lock file left behind by the incomplete git command resolved the
> issue, indicating a potential bug in how "git stash" handles incomplete
> commands.
> *Recommendation:*

> 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).

> 
> Reported-by: moti sd <motisd8@gmail.com>
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  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
> 

> 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?

> > 
> > Reported-by: moti sd <motisd8@gmail.com>
> > Signed-off-by: Patrick Steinhardt <ps@pks.im>
> > ---
> >  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
> > 
> 
> 

> 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).

> @@ -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;
>  	}
>  

> Patrick Steinhardt <ps@pks.im> writes:
> 
> > 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.
> 
> Hopefully, they know they notice the exit status of the command, or
> do we throw the error away and exit(0) from the program?

> In any case, telling the users what did (and did not) happen is a
> good idea.
> 
> > 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).
> 
> Style may be OK, but I wonder if they should say different things,
> to hint what failed.  For example:
> 
> > @@ -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))
> 
> This failure and message comes before anything interesting happens.
> We attempted to refresh the current index and failed to write out
> the result, meaning that whatever index we had on disk did not get
> overwritten.  Is this new message enough to tell the user that we
> didn't touch the working tree or the index, which would happen if
> even some part of "stash apply" happened?  Or is it obvious that we
> did not do anything?