[v2,0/1] t6042: fix breakage on Windows

Message

Bruce Perry via GitGitGadget Jan. 17, 2019, 8:29 a.m. UTC

Unfortunately, Travis decided to change some things under the hood that
affect the Windows build. As a consequence, master has not been tested in
quite a while, even if the test runs pretended that it had been tested :-(

So imagine my surprise when master simply would refuse to pass the test
suite cleanly outside Travis, always failing at t6042, despite the fact that
Travis passed.

It turns out that two files are written too quickly in succession, running
into the issue where Git for Windows chooses not to populate the inode and
device numbers in the stat data (this is a noticeable performance
optimization). As a consequence, Git thinks the file is unchanged, and fails
to pick up a modification. And no, we cannot simply undo the performance
optimization, it would make things prohibitively slow in particular in large
worktrees, and it is not like the bug is likely to be hit in reality: for
Git to be fooled into thinking that a file is unchanged, it has to be
written with the same file size, and within a 100ns time bucket (it is
pretty improbable that there is any real-world scenario that would run into 
that, except of course our regression test suite).

This patch works around this issue by forcing Git to recognize the new file
versions as new files (which they really are: the patch simply replaces

git mv <old> <new> && mv <file> <new> && git add <new>`

by

git rm <old> && mv <file> <new> && git add <new>`

which is not shorter, but even a performance improvement (an unnoticeable
one, of course).

Changes since v1:

 * Clarified the change in the commit message.

Johannes Schindelin (1):
  t6042: work around speed optimization on Windows

 t/t6042-merge-rename-corner-cases.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)


base-commit: 77556354bb7ac50450e3b28999e3576969869068
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-109%2Fdscho%2Ffix-t6042-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-109/dscho/fix-t6042-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/109

Range-diff vs v1:

 1:  598de6652c ! 1:  55b0a641d4 t6042: work around speed optimization on Windows
     @@ -35,6 +35,12 @@
          now add the files as new files (as opposed to existing, just renamed
          files).
      
     +    Functionally, we do not change anything because we replace two `git mv
     +    <old> <new>` calls (where `<new>` is completely overwritten and `git
     +    add`ed later anyway) by `git rm <old>` calls (removing other files, too,
     +    that are also completely overwritten and `git add`ed later).
     +
     +    Reviewed-by: Elijah Newren <[e-mail]>
          Signed-off-by: Johannes Schindelin <[e-mail]>
      
       diff --git a/t/t6042-merge-rename-corner-cases.sh b/t/t6042-merge-rename-corner-cases.sh