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-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.