Re: [PATCH 1/2] merge: fix numerus bugs around "trivial merge" area

Junio C Hamano [off-list ref] writes:

The primary logic of the merge, however, had an assumption that the
process never read the index in-core, and write_cache_as_tree() call it
makes from write_tree_trivial() will always read from the on-disk index
the strategies created and write it out as a tree.  This assumption is now
broken by the above fix.  It now calls discard_cache() before calling
write_tree_trivial() when it wants to write the on-disk index as a tree to
fix this issue.

By the way, in the medium term, if we are serious about making an internal
call to merge_recursive() from cmd_merge(), I think we may be better off
making it the responsibility for try_merge_strategy() to leave an
committable state in the in-core index (aka "the_index") when they return
with 0 (success) status.  After calling external ones via the run_command
interface, it should do a read_cache() (after calling discard_cache() if
needed); if it calls merge_recursive(), hopefully you already have the
committable state in the in-core index.

That way, when automerge succeeds, write_tree_trivial() can write that
in-core index out and create the tree object to be committed. The
callchain to use merge_recursive() can avoid having to write to the
on-disk index, read it again and write out the tree from it.