From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jonathan Nieder <jrnieder@gmail.com>
Subject: Re: [PATCH 2/3] do not write null sha1s to on-disk index
Date: Sat, 29 Dec 2012 02:03:46 -0800
Message-ID: <20121229100130.GA31497@elie.Belkin>
References: <20120728150132.GA25042@sigill.intra.peff.net>
 <20120728150524.GB25269@sigill.intra.peff.net>
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Cc: git@vger.kernel.org, Jens Lehmann <Jens.Lehmann@web.de>,
	Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
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Hi Peff,

Jeff King wrote:

> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -1800,6 +1800,8 @@ int write_index(struct index_state *istate, int newfd)
>  			continue;
>  		if (!ce_uptodate(ce) && is_racy_timestamp(istate, ce))
>  			ce_smudge_racily_clean_entry(ce);
> +		if (is_null_sha1(ce->sha1))
> +			return error("cache entry has null sha1: %s", ce->name);
>  		if (ce_write_entry(&c, newfd, ce, previous_name) < 0)
>  			return -1;

Quick heads up: this is tripping for me in the "git am --abort"
codepath:

  $ cd ~/src/linux
  $ git checkout v3.2.35
  $ git am -3sc /tmp/alsa-usb-audio-fix-missing-autopm-for-midi-input.patch 
  Applying: ALSA: usb-audio: Fix missing autopm for MIDI input
  Using index info to reconstruct a base tree...
  Falling back to patching base and 3-way merge...
  error: Your local changes to the following files would be overwritten by merge:
	sound/usb/midi.c
  Please, commit your changes or stash them before you can merge.
  Aborting
  Failed to merge in the changes.
  Patch failed at 0001 ALSA: usb-audio: Fix missing autopm for MIDI input
  When you have resolved this problem run "git am --resolved".
  If you would prefer to skip this patch, instead run "git am --skip".
  To restore the original branch and stop patching run "git am --abort".
  $ git am --abort
  error: cache entry has null sha1: sound/usb/midi.c
  fatal: unable to write new index file
  Unstaged changes after reset:
  M       sound/usb/midi.c
  $

Reproducible using v1.8.1-rc3 and master.  Bisects to 4337b585 (do not
write null sha1s to on-disk index, 2012-07-28).  For comparison, older
gits produced

  $ git am --abort
  Unstaged changes after reset:
  M       sound/usb/midi.c

which is also not great but at least didn't involve any obviously
invalid behavior.  Known problem?

Thanks,
Jonathan