Subject: Re: [PATCH v4 02/15] branch: die on error in setting up tracking branch

From: Patrick Steinhardt <[email-masked]>
Date: Mon, 8 Feb 2016 14:42:32 +0100

On Tue, Feb 02, 2016 at 12:49:26PM -0800, Junio C Hamano wrote:
> Patrick Steinhardt <[email-masked]> writes:
> 
> > The setup_tracking function calls install_branch_config, which
> > may fail writing the configuration due to a locked configuration
> > file or other error conditions. setup_tracking can also fail when
> > trying to track ambiguous information for a reference. While this
> > condition is checked for and an error code is returned, this
> > error is not checked by the caller.
> >
> > Fix both issues by dying early when error occur.
> 
> Hmph.  I think create_branch() is written in such a way that all
> die() come before the actual ref transaction attempts to create the
> branch, but this change means that we have already created the
> branch and then die without undoing the damage that is already done.
> 
> "The error is not checked by the caller" is very true, but can the
> caller do something better than just die?  I personally do not think
> it is such a big deal if we just died here, but I may have overlooked
> something.

Well, when dying here we do not record the tracking branch
configuration for the newly set up branch. This is the only thing
that we are missing as right after setting up the tracking branch
we've finished and exit the command.

That being said it's somewhat unfortunate to die here as the user
cannot simply try to repeat creating a branch and hope it works
this time as the branch has already been created and the command
would error out. Maybe we should instead die with an improved
error message hinting the user how to fix the issue, something
along the lines of

"We were unable to set the remote tracking information for the
newly created branch due to <REASON>. After fixing the underlying
problem you may set the remote tracking branch by executing `git
branch --set-upstream-to=<BRANCH>."

> > ---
> >  branch.c          | 19 +++++++++----------
> >  branch.h          |  1 +
> >  t/t3200-branch.sh |  9 ++++++++-
> >  3 files changed, 18 insertions(+), 11 deletions(-)
> >
> > diff --git a/branch.c b/branch.c
> > index 7ff3f20..7106369 100644
> > --- a/branch.c
> > +++ b/branch.c
> > @@ -64,16 +64,16 @@ void install_branch_config(int flag, const char *local, const char *origin, cons
> >  	}
> >  
> >  	strbuf_addf(&key, "branch.%s.remote", local);
> > -	git_config_set(key.buf, origin ? origin : ".");
> > +	git_config_set_or_die(key.buf, origin ? origin : ".");
> >  
> >  	strbuf_reset(&key);
> >  	strbuf_addf(&key, "branch.%s.merge", local);
> > -	git_config_set(key.buf, remote);
> > +	git_config_set_or_die(key.buf, remote);
> >  
> >  	if (rebasing) {
> >  		strbuf_reset(&key);
> >  		strbuf_addf(&key, "branch.%s.rebase", local);
> > -		git_config_set(key.buf, "true");
> > +		git_config_set_or_die(key.buf, "true");
> >  	}
> >  	strbuf_release(&key);
> >  
> > @@ -109,8 +109,8 @@ void install_branch_config(int flag, const char *local, const char *origin, cons
> >   * to infer the settings for branch.<new_ref>.{remote,merge} from the
> >   * config.
> >   */
> > -static int setup_tracking(const char *new_ref, const char *orig_ref,
> > -			  enum branch_track track, int quiet)
> > +static void setup_tracking(const char *new_ref, const char *orig_ref,
> > +			   enum branch_track track, int quiet)
> >  {
> >  	struct tracking tracking;
> >  	int config_flags = quiet ? 0 : BRANCH_CONFIG_VERBOSE;
> > @@ -118,7 +118,7 @@ static int setup_tracking(const char *new_ref, const char *orig_ref,
> >  	memset(&tracking, 0, sizeof(tracking));
> >  	tracking.spec.dst = (char *)orig_ref;
> >  	if (for_each_remote(find_tracked_branch, &tracking))
> > -		return 1;
> > +		return;
> >  
> >  	if (!tracking.matches)
> >  		switch (track) {
> > @@ -127,18 +127,17 @@ static int setup_tracking(const char *new_ref, const char *orig_ref,
> >  		case BRANCH_TRACK_OVERRIDE:
> >  			break;
> >  		default:
> > -			return 1;
> > +			return;
> >  		}
> >  
> >  	if (tracking.matches > 1)
> > -		return error(_("Not tracking: ambiguous information for ref %s"),
> > -				orig_ref);
> > +		die(_("Not tracking: ambiguous information for ref %s"),
> > +		    orig_ref);
> >  
> >  	install_branch_config(config_flags, new_ref, tracking.remote,
> >  			      tracking.src ? tracking.src : orig_ref);
> >  
> >  	free(tracking.src);
> > -	return 0;
> >  }
> >  
> >  int read_branch_desc(struct strbuf *buf, const char *branch_name)
> > diff --git a/branch.h b/branch.h
> > index 58aa45f..8ce22f8 100644
> > --- a/branch.h
> > +++ b/branch.h
> > @@ -43,6 +43,7 @@ void remove_branch_state(void);
> >  /*
> >   * Configure local branch "local" as downstream to branch "remote"
> >   * from remote "origin".  Used by git branch --set-upstream.
> > + * Dies if unable to install branch config.
> >   */
> >  #define BRANCH_CONFIG_VERBOSE 01
> >  extern void install_branch_config(int flag, const char *local, const char *origin, const char *remote);
> > diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
> > index cdaf6f6..dd776b3 100755
> > --- a/t/t3200-branch.sh
> > +++ b/t/t3200-branch.sh
> > @@ -446,6 +446,13 @@ test_expect_success '--set-upstream-to fails on a non-ref' '
> >  	test_must_fail git branch --set-upstream-to HEAD^{}
> >  '
> >  
> > +test_expect_success '--set-upstream-to fails on locked config' '
> > +	test_when_finished "rm -f .git/config.lock" &&
> > +	>.git/config.lock &&
> > +	git branch locked &&
> > +	test_must_fail git branch --set-upstream-to locked
> > +'
> > +
> >  test_expect_success 'use --set-upstream-to modify HEAD' '
> >  	test_config branch.master.remote foo &&
> >  	test_config branch.master.merge foo &&
> > @@ -579,7 +586,7 @@ test_expect_success 'avoid ambiguous track' '
> >  	git config remote.ambi1.fetch refs/heads/lalala:refs/heads/master &&
> >  	git config remote.ambi2.url lilili &&
> >  	git config remote.ambi2.fetch refs/heads/lilili:refs/heads/master &&
> > -	git branch all1 master &&
> > +	test_must_fail git branch all1 master &&
> >  	test -z "$(git config branch.all1.merge)"
> >  '