115 lines
4.8 KiB
Text
115 lines
4.8 KiB
Text
Directory rename detection
|
|
==========================
|
|
|
|
Rename detection logic in diffcore-rename that checks for renames of
|
|
individual files is aggregated and analyzed in merge-recursive for cases
|
|
where combinations of renames indicate that a full directory has been
|
|
renamed.
|
|
|
|
Scope of abilities
|
|
------------------
|
|
|
|
It is perhaps easiest to start with an example:
|
|
|
|
* When all of x/a, x/b and x/c have moved to z/a, z/b and z/c, it is
|
|
likely that x/d added in the meantime would also want to move to z/d by
|
|
taking the hint that the entire directory 'x' moved to 'z'.
|
|
|
|
More interesting possibilities exist, though, such as:
|
|
|
|
* one side of history renames x -> z, and the other renames some file to
|
|
x/e, causing the need for the merge to do a transitive rename.
|
|
|
|
* one side of history renames x -> z, but also renames all files within x.
|
|
For example, x/a -> z/alpha, x/b -> z/bravo, etc.
|
|
|
|
* both 'x' and 'y' being merged into a single directory 'z', with a
|
|
directory rename being detected for both x->z and y->z.
|
|
|
|
* not all files in a directory being renamed to the same location;
|
|
i.e. perhaps most the files in 'x' are now found under 'z', but a few
|
|
are found under 'w'.
|
|
|
|
* a directory being renamed, which also contained a subdirectory that was
|
|
renamed to some entirely different location. (And perhaps the inner
|
|
directory itself contained inner directories that were renamed to yet
|
|
other locations).
|
|
|
|
* combinations of the above; see t/t6043-merge-rename-directories.sh for
|
|
various interesting cases.
|
|
|
|
Limitations -- applicability of directory renames
|
|
-------------------------------------------------
|
|
|
|
In order to prevent edge and corner cases resulting in either conflicts
|
|
that cannot be represented in the index or which might be too complex for
|
|
users to try to understand and resolve, a couple basic rules limit when
|
|
directory rename detection applies:
|
|
|
|
1) If a given directory still exists on both sides of a merge, we do
|
|
not consider it to have been renamed.
|
|
|
|
2) If a subset of to-be-renamed files have a file or directory in the
|
|
way (or would be in the way of each other), "turn off" the directory
|
|
rename for those specific sub-paths and report the conflict to the
|
|
user.
|
|
|
|
3) If the other side of history did a directory rename to a path that
|
|
your side of history renamed away, then ignore that particular
|
|
rename from the other side of history for any implicit directory
|
|
renames (but warn the user).
|
|
|
|
Limitations -- detailed rules and testcases
|
|
-------------------------------------------
|
|
|
|
t/t6043-merge-rename-directories.sh contains extensive tests and commentary
|
|
which generate and explore the rules listed above. It also lists a few
|
|
additional rules:
|
|
|
|
a) If renames split a directory into two or more others, the directory
|
|
with the most renames, "wins".
|
|
|
|
b) Avoid directory-rename-detection for a path, if that path is the
|
|
source of a rename on either side of a merge.
|
|
|
|
c) Only apply implicit directory renames to directories if the other side
|
|
of history is the one doing the renaming.
|
|
|
|
Limitations -- support in different commands
|
|
--------------------------------------------
|
|
|
|
Directory rename detection is supported by 'merge' and 'cherry-pick'.
|
|
Other git commands which users might be surprised to see limited or no
|
|
directory rename detection support in:
|
|
|
|
* diff
|
|
|
|
Folks have requested in the past that `git diff` detect directory
|
|
renames and somehow simplify its output. It is not clear whether this
|
|
would be desirable or how the output should be simplified, so this was
|
|
simply not implemented. Further, to implement this, directory rename
|
|
detection logic would need to move from merge-recursive to
|
|
diffcore-rename.
|
|
|
|
* am
|
|
|
|
git-am tries to avoid a full three way merge, instead calling
|
|
git-apply. That prevents us from detecting renames at all, which may
|
|
defeat the directory rename detection. There is a fallback, though; if
|
|
the initial git-apply fails and the user has specified the -3 option,
|
|
git-am will fall back to a three way merge. However, git-am lacks the
|
|
necessary information to do a "real" three way merge. Instead, it has
|
|
to use build_fake_ancestor() to get a merge base that is missing files
|
|
whose rename may have been important to detect for directory rename
|
|
detection to function.
|
|
|
|
* rebase
|
|
|
|
Since am-based rebases work by first generating a bunch of patches
|
|
(which no longer record what the original commits were and thus don't
|
|
have the necessary info from which we can find a real merge-base), and
|
|
then calling git-am, this implies that am-based rebases will not always
|
|
successfully detect directory renames either (see the 'am' section
|
|
above). merged-based rebases (rebase -m) and cherry-pick-based rebases
|
|
(rebase -i) are not affected by this shortcoming, and fully support
|
|
directory rename detection.
|