If read_tree_trivial() succeeds and produces a tree that is already
in the object store, then the index is not written to disk, leaving
it out-of-sync with both HEAD and the working tree.
In order to write the index back out to disk after a merge,
write_index_locked() needs to be called. For most merge strategies, this
is done from try_merge_strategy(). For fast forward updates, this is
done from checkout_fast_forward(). When trivial merges work, the call to
write_index_locked() is buried a little deeper:
merge_trivial()
-> write_tree_trivial()
-> write_cache_as_tree()
-> write_index_as_tree()
-> write_locked_index()
However, it is only called when !cache_tree_fully_valid(), which is how
this bug is triggered. But that also shows why this bug doesn't affect
any other merge strategies or cases.
Add a direct call to write_index_locked() from merge_trivial() to fix
this issue. Since the indirect call to write_locked_index() was
conditional on cache_tree_fully_valid(), it won't be written twice.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Repeating a trivial merge more than once will leave the index out of
sync, despite being clean before the merge and operating on the
exact same heads as the first run. The recorded merge has the
correct tree and the working tree is brought up to date, it is just
the index that is left as it was before the merge. Every attempt to
repeat the merge beyond the first will leave the index in the same
weird out-of-sync state.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "trivial merge" codepath wants to optimize itself by making an
internal call to the read-tree machinery, but it does not read the index
before doing so, and the codepath is never exercised. Incidentally, this
failure to read the index upfront means that the safety to refuse doing
anything when the index is unmerged does not kick in, either.
These two problem are fixed by using read_cache_unmerged() that does read
the index before checking if it is unmerged at the beginning of
cmd_merge().
The primary logic of the merge, however, assumes that the process never
reads the index in-core, and the call to write_cache_as_tree() it makes
from write_tree_trivial() will always read from the on-disk index that is
prepared the strategy back-ends. This assumption is now broken by the
above fix. To fix this issue, we now call discard_cache() before calling
write_tree_trivial() when it wants to write the on-disk index as a tree.
When multiple strategies are tried, their results are evaluated by reading
the resulting index and inspecting it. The codepath needs to make a call
to read_cache() for each successful strategy, and for that to work, they
need to discard_cache() the one read by the previous round.
Also the "trivial merge" forgot that the current commit is one of the
parents of the resulting commit.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Actually this is a simple test, just to ensure merge-resolve properly
calls read-tree. read-tree itself already has more complex tests.
Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
