Re: [PATCH] commit: write out cache-tree information

[off-list ref] writes:

From: Thomas Rast <redacted>

While write-tree has code to write out the cache-tree information
(since we have to compute it anyway if the cache is stale), commit
lost this capability when it became a builtin and moved away from
using write-tree.

Earlier the code read from the index, made sure that it is not unmerged by
running cache_tere_update(), before running prepare-commit-msg hook. The
hook used to see the index that was read in this codepath which is the
same as what pre-commit left us.

Why run an extra I/O here? The index file could be quite large, and I do
not want people to writing it out without good reason.

The tree object that is committed is taken from active_cache_tree->sha1 in
cmd_commit() and not from the cache tree you are writing out to the index
file.