builtin/merge.c says that when we are about to perform a merge:
...the index must be in sync with the head commit. The strategies are
responsible to ensure this.
merge-recursive has always relied on unpack_trees() to enforce this
requirement, except in the case of an "Already up to date!" merge.
unpack-trees.c does not actually enforce this requirement, though. It
allows for a pair of exceptions, in cases which it refers to as #14(ALT)
and #2ALT. Documentation/technical/trivial-merge.txt can be consulted for
the precise meanings of the various case numbers and their meanings for
unpack-trees.c, but we have a high-level description of the intent behind
these two exceptions in a combined and summarized form in
Documentation/git-merge.txt:
...[merge will] abort if there are any changes registered in the index
relative to the `HEAD` commit. (One exception is when the changed index
entries are in the state that would result from the merge already.)
While this high-level description does describe conditions under which it
would be safe to allow the index to diverge from HEAD, it does not match
what is actually implemented. In particular, unpack-trees.c has no
knowledge of renames, and these two exceptions were written assuming that
no renames take place. Once renames get into the mix, it is no longer
safe to allow the index to not match for #2ALT. We could modify
unpack-trees to only allow #14(ALT) as an exception, but that would be
more strict than required for the resolve strategy (since the resolve
strategy doesn't handle renames at all). Therefore, unpack_trees.c seems
like the wrong place to fix this.
Further, if someone fixes the combination of break and rename detection
and modifies merge-recursive to take advantage of the combination, then it
will also no longer be safe to allow the index to not match for #14(ALT)
when the recursive strategy is in use. Therefore, leaving one of the
exceptions in place with the recursive merge strategy feels like we are
just leaving a latent bug in the code for folks in the future to stumble
across.
It may be possible to fix both unpack-trees and merge-recursive in a way
that implements the exception as stated in Documentation/git-merge.txt,
but it would be somewhat complex, possibly also buggy at first, and
ultimately, not all that valuable. Instead, just enforce the requirement
stated in builtin/merge.c; error out if the index does not match the HEAD
commit, just like the 'ours' and 'octopus' strategies do.
Some testcase fixups were in order:
t7611: had many tests designed to show that `git merge --abort` could
not always restore the index and working tree to the state they
were in before the merge started. The tests that were associated
with having changes in the index before the merge started are no
longer applicable, so they have been removed.
t7504: had a few tests that had stray staged changes that were not
actually part of the test under consideration
t6044: We no longer expect stray staged changes to sometimes result
in the merge continuing. Also, fix a case where a merge
didn't abort but should have.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
According to Documentation/git-merge.txt,
...[merge will] abort if there are any changes registered in the index
relative to the `HEAD` commit. (One exception is when the changed
index entries are in the state that would result from the merge
already.)
Add some tests showing that this exception, while it does accurately state
what would be a safe condition under which we could allow the merge to
proceed, is not what is actually implemented.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
`git merge-recursive` does a three-way merge between user-specified trees
base, head, and remote. Since the user is allowed to specify head, we can
not necesarily assume that head == HEAD.
Modify index_has_changes() to take an extra argument specifying the tree
to compare against. If NULL, it will compare to HEAD. We then use this
from merge-recursive to make sure we compare to the user-specified head.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In commit 65170c07d4 ("merge-recursive: avoid incorporating uncommitted
changes in a merge", 2017-12-21), it was noted that there was a special
case when merge-recursive didn't rely on unpack_trees() to enforce the
index == HEAD requirement, and thus that it needed to do that enforcement
itself. Unfortunately, it returned the wrong exit status, signalling that
the merge completed but had conflicts, rather than that it was aborted.
Fix the return code, and while we're at it, change the error message to
match what unpack_trees() would have printed.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `git merge-recursive` command allows the user to directly specify
three commits to merge -- base, head, and remote. (More than three can be
specified in the case of multiple merge bases.) Note that since the user
is allowed to specify head, it need not match HEAD.
Virtually every test and script in the current git.git codebase calls `git
merge-recursive` with head=HEAD, and likely external callers do as well,
which is why this has gone unnoticed. There is one notable
counter-example: git-stash.sh. However, git-stash called `git
merge-recursive` with an index that matches the expected merge result,
which happens to be a currently allowed exception to the "index must match
head" rule, so this never triggered an error previously.
Since we would like to tighten up the "index must match head" rule, we
need to make sure we are comparing to the correct head. Add a testcase
that demonstrates the failure when we check the wrong HEAD.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
t6044 has lots of tests for verifying that merge will abort as expected
when there are changes staged before the merge starts. However, it only
checked for non-zero exit code, which could mean that the merge ran to
completion with conflicts. Check that the merge was actually correctly
aborted, i.e. that .git/MERGE_HEAD is not present.
This changes one of the tests from expect_success to expect_failure.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
builtin/merge.c contains this important requirement for merge strategies:
/*
* At this point, we need a real merge. No matter what strategy
* we use, it would operate on the index, possibly affecting the
* working tree, and when resolved cleanly, have the desired
* tree in the index -- this means that the index must be in
* sync with the head commit. The strategies are responsible
* to ensure this.
*/
merge-recursive does not do this check directly, instead it relies on
unpack_trees() to do it. However, merge_trees() has a special check for
the merge branch exactly matching the merge base; when it detects that
situation, it returns early without calling unpack_trees(), because it
knows that the HEAD commit already has the correct result. Unfortunately,
it didn't check that the index matched HEAD, so after it returned, the
outer logic ended up creating a merge commit that included something
other than HEAD.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The recursive merge strategy has some special handling when the tree for
the merge branch exactly matches the merge base, but that code path is
missing checks for the index having changes relative to HEAD. Add a
testcase covering this scenario.
Reported-by: Andreas Krey <a.krey@gmx.de>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
With one exception, we require the index to exactly match the
current HEAD commit at the time git merge is invoked. This
expectation was even documented in git-merge.txt until commit
ebef7e5 (Documentation: simplify How Merge Works, 2010-01-23).
Most merge strategies enforced this requirement, but it turns out
not all did. The current exceptions were the following two:
* ff updates
* octopus merges
ff updates actually will error out if the staged change is to a path
modified between HEAD and the commit being merged. If the path(s)
that are staged are files unrelated to the changes between these two
commits, though, then an ff update will just keep these staged
changes around after the merge. This is the one exception we
expected to the abort-merge-if- index-doesn't-match-HEAD rule.
For octopus merges, the rule should be enforced. Unfortunately, the
current behavior of the code is to ignore the difference and use the
staged changes in place of whatever is in HEAD as it proceeds to
perform the merge. So if the staged changes can be cleanly merged
with all the other heads, then the staged changes will just be
incorported into the resulting commit. If the staged changes cannot
be cleanly merged with all the other heads, the merge is not aborted
-- merge conflicts are simply reported as if HEAD had originally
contained whatever the index did.
Add testcases that check our expectations. A subsequent commit will
correct the erroneous octopus merge behavior.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
