[PATCH] read-cache.c: Ensure unmerged entries are removed

A file in the index can be left as merged and unmerged at the same time by some tools as libgit2, this causes some undesiderable behaviours in git.

I have seen, at least, these behaviours:
- git reset --hard consuming 100% CPU and never ending
- git reset --hard consuming all memory in git < 2.0
- git add/git mergetool not resolving a conflict, even if they finish
  succesfully

The state is something like this:

$ git ls-files -s 100644 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 0 conflict 100644 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 1 conflict 100644 5716ca5987cbf97d6bb54920bea6adde242d87e6 2 conflict 100644 f2e41136eac73c39554dede1fd7e67b12502d577 3 conflict

This can be caused e.g. by libgit2 doing this:
1. Merge with conflicts, without solving them
2. Force checkout

I see that this is not caused by git (I haven't been able to reproduce it only using git) but I think that git should be able to detect this situation and even handle it, specially to avoid the never-ending git resets.

The proposed patch serves as protection and autoremediation for this kind of cases. Another option would be to detect the issue and tell the user to clean the index with git read-tree --empty, but I think this would be more intrussive than the patch.

Regards, Jaime Soriano.

Jaime Soriano Pastor (1):
  read-cache.c: Ensure unmerged entries are removed

 read-cache.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)