Re: [PATCH v6 08/42] refs.c: change ref_transaction_update() to do error checking and return status

On Wed, May 14, 2014 at 4:40 PM, Jonathan Nieder [off-list ref] wrote:

Ronnie Sahlberg wrote:

quoted

Update ref_transaction_update() do some basic error checking and return
true on error. Update all callers to check ref_transaction_update() for error.
There are currently no conditions in _update that will return error but there
will be in the future.

Signed-off-by: Ronnie Sahlberg <redacted>
---
 builtin/update-ref.c | 10 ++++++----
 refs.c               |  9 +++++++--
 refs.h               | 10 +++++-----
 3 files changed, 18 insertions(+), 11 deletions(-)

Revisiting comments from [1]:

 * When I call ref_transaction_update, what does it mean that I get
   a nonzero return value?  Does it mean the _update failed and had
   no effect?  What will I want to do next: should I try again or
   print an error and exit?

It means the transaction will no longer work and must be rolled back.
See below for the updated text I added to refs.h

   Ideally I should be able to answer these questions by reading
   the signature of ref_transaction_update and the comment documenting
   it.  The comment doesn't say anything about what errors
   mean here.

I have updated the description to include :
 * Function returns 0 on success and non-zero on failure. A failure to update
 * means that the transaction as a whole has failed and will need to be
 * rolled back.

 * the error message change for the have_old && !old_sha1 case (to add
   "BUG:" so users know the impossible has happened and translators
   know not to bother with it) seems to have snuck ahead into patch 28
   (refs.c: add transaction.status and track OPEN/CLOSED/ERROR).

Done.

 * It would be easier to make sense of the error path (does the error
   message have enough information?  Will the user be bewildered?)
   if there were an example of how ref_transaction_update can fail.

   There still doesn't seem to be one by the end of the series.

This patch series got a lot longer than I initially thought so I did
not get to the point where we it would make sense
to start returning !0. :-(

The next patchseries I sent out for review does add things to _update
that will cause it to return failures.
For example, locking the ref there happens in _update instead of
_commit and then it starts make sense to
return failures back to the caller for things such as "Multiple
updates for ref '%s' not allowed."

Unfortunate but since this patch series reached >40 patches I did not
want to continue expanding on it.
This means that actually starting to use "let _update return error"
did not actually start becomming used until the second
patch series, which now is well over 30 patches in size :-(

I just felt I had to stop growing this series or it would never be finished.

The general idea still seems sensible.

Thanks,
Jonathan

[1] http://thread.gmane.org/gmane.comp.version-control.git/246437/focus=247115