Git's rename detection requires a stable sort #352
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…ears/next See gitgitgadget#352 Signed-off-by: Johannes Schindelin <[email protected]>
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The `qsort()` function is not guaranteed to be stable, i.e. it does not promise to maintain the order of items it is told to consider equal. In contrast, the `git_sort()` function we carry in `compat/qsort.c` _is_ stable, by virtue of implementing a merge sort algorithm. In preparation for using a stable sort in Git's rename detection, move the stable sort into `libgit.a` so that it is compiled in unconditionally, and rename it to `git_stable_qsort()`. Note: this also makes the hack obsolete that was introduced in fe21c6b (mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8), 2018-10-30), where we included `compat/qsort.c` directly in `compat/mingw.c` to use the stable sort. Signed-off-by: Johannes Schindelin <[email protected]>
During Git's rename detection, the file names are sorted. At the moment, this job is performed by `qsort()`. As that function is not guaranteed to implement a stable sort algorithm, this can lead to inconsistent and/or surprising behavior: a rename might be detected differently depending on the platform where Git was run. The `qsort()` in MS Visual C's runtime does _not_ implement a stable sort algorithm, and it even leads to an inconsistency leading to a test failure in t3030.35 "merge-recursive remembers the names of all base trees": a different code path than on Linux is taken in the rename detection of an ambiguous rename between either `e` to `a` or `a~Temporary merge branch 2_0` to `a` during a recursive merge, unexpectedly resulting in a clean merge. Let's use the stable sort provided by `git_stable_qsort()` to avoid this inconsistency. Signed-off-by: Johannes Schindelin <[email protected]>
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…ears/next See gitgitgadget#352 Signed-off-by: Johannes Schindelin <[email protected]>
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This patch series was integrated into pu via git@aaf27a8. |
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…ears/next See gitgitgadget#352 Signed-off-by: Johannes Schindelin <[email protected]>
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This patch series was integrated into pu via git@016da89. |
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This patch series was integrated into pu via git@9c79a23. |
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This patch series was integrated into pu via git@b699e49. |
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This patch series was integrated into pu via git@772cad0. |
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With the
en/merge-recursive-cleanuppatches already having advanced tonext, the problem I discovered when rebasing Git for Windows' branch thicket becomes quite relevant now: t3030.35 fails consistently in the MSVC build & test (this part of the Azure Pipeline will be upstreamed later).The solution: use a stable sort.
Note: this patch series is based on top of
en/merge-recursive-cleanup.Changes since v1:
git_stable_qsort(), as per Junio's suggestion.