fetch: delay user information post committing of transaction

In Git 2.50 and earlier, we would display failure codes and error
message as part of the status display:

  $ git fetch . v1.0.0:refs/heads/foo
    error: cannot update ref 'refs/heads/foo': trying to write non-commit object f665776185ad074b236c00751d666da7d1977dbe to branch 'refs/heads/foo'
    From .
     ! [new tag]               v1.0.0     -> foo  (unable to update local ref)

With the addition of batched updates, this information is no longer
shown to the user:

  $ git fetch . v1.0.0:refs/heads/foo
    From .
     * [new tag]               v1.0.0     -> foo
    error: cannot update ref 'refs/heads/foo': trying to write non-commit object f665776185ad074b236c00751d666da7d1977dbe to branch 'refs/heads/foo'

Since reference updates are batched and processed together at the end,
information around the outcome is not available during individual
reference parsing.

To overcome this, collate and delay the output to the end. Introduce
`ref_update_display_info` which will hold individual update's
information and also whether the update failed or succeeded. This
finally allows us to iterate over all such updates and print them to the
user.

Using an dynamic array and strmap does add some overhead to
'git-fetch(1)', but from benchmarking this seems to be not too bad:

  Benchmark 1: fetch: many refs (refformat = files, refcount = 1000, revision = master)
    Time (mean ± σ):      42.6 ms ±   1.2 ms    [User: 13.1 ms, System: 29.8 ms]
    Range (min … max):    40.1 ms …  45.8 ms    47 runs

  Benchmark 2: fetch: many refs (refformat = files, refcount = 1000, revision = HEAD)
    Time (mean ± σ):      43.1 ms ±   1.2 ms    [User: 12.7 ms, System: 30.7 ms]
    Range (min … max):    40.5 ms …  45.8 ms    48 runs

  Summary
    fetch: many refs (refformat = files, refcount = 1000, revision = master) ran
      1.01 ± 0.04 times faster than fetch: many refs (refformat = files, refcount = 1000, revision = HEAD)

Another approach would be to move the status printing logic to be
handled post the transaction being committed. That however would require
adding an iterator to the ref transaction that tracks both the outcome
(success/failure) and the original refspec information for each update,
which is more involved infrastructure work compared to the strmap
approach here.

Helped-by: Phillip Wood <phillip.wood123@gmail.com>
Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

0 files changed, 0 insertions, 0 deletions