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authorLibravatar Elijah Newren <newren@gmail.com>2021-03-11 00:38:28 +0000
committerLibravatar Junio C Hamano <gitster@pobox.com>2021-03-10 22:18:05 -0800
commit2fd9eda462088b7ef992e9f5abd1658d942b3923 (patch)
tree9926343bd0f5d2033d77f9c40af59ee1b7e3488f /git-cvsexportcommit.perl
parentmerge-ort: introduce wrappers for alternate tree traversal (diff)
downloadtgif-2fd9eda462088b7ef992e9f5abd1658d942b3923.tar.xz
merge-ort: precompute whether directory rename detection is needed
The point of directory rename detection is that if one side of history renames a directory, and the other side adds new files under the old directory, then the merge can move those new files into the new directory. This leads to the following important observation: * If the other side does not add any new files under the old directory, we do not need to detect any renames for that directory. Similarly, directory rename detection had an important requirement: * If a directory still exists on one side of history, it has not been renamed on that side of history. (See section 4 of t6423 or Documentation/technical/directory-rename-detection.txt for more details). Using these two bits of information, we note that directory rename detection is only needed in cases where (1) directories exist in the merge base and on one side of history (i.e. dirmask == 3 or dirmask == 5), and (2) where there is some new file added to that directory on the side where it still exists (thus where the file has filemask == 2 or filemask == 4, respectively). This has to be done in two steps, because we have the dirmask when we are first considering the directory, and won't get the filemasks for the files within it until we recurse into that directory. So, we save dir_rename_mask = dirmask - 1 when we hit a directory that is missing on one side, and then later look for cases of filemask == dir_rename_mask One final note is that as soon as we hit a directory that needs directory rename detection, we will need to detect renames in all subdirectories of that directory as well due to the "majority rules" decision when files are renamed into different directory hierarchies. We arbitrarily use the special value of 0x07 to record when we've hit such a directory. The combination of all the above mean that we introduce a variable named dir_rename_mask (couldn't think of a better name) which has one of the following values as we traverse into a directory: * 0x00: directory rename detection not needed * 0x02 or 0x04: directory rename detection only needed if files added * 0x07: directory rename detection definitely needed We then pass this value through to add_pairs() so that it can mark location_relevant as true only when dir_rename_mask is 0x07. Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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