Cache high-resolution mtimes for improved detection of modified files in v7
(and direct mode).
Including on Windows.
With back-compat support so old low-res mtimes won't break anything, and
so the new information also won't break old versions of git-annex.
I've seen intermittent failures of the test suite with v6 for a long time,
it seems to have possibly gotten worse with the changes around v7. Or just
being unlucky; all tests failed today.
Seen on amd64 and i386 builders, repeatedly but intermittently:
unused: FAIL (4.86s)
Test.hs:928:
git diff did not show changes to unlocked file
And I think other such failures, all involving v7/v6 mode tests.
I managed to reproduce the unused failure with --keep-failures,
and inside the repo, git diff was indeed not showing any changes for
the modified unlocked file.
The two stats will be the same other than mtime; the old and new files have
the same size and inode, since the test case writes to the file and then
overwrites it.
Indeed, notice the identical timestamps:
builder@orca:~/gitbuilder/build/.t/tmprepo335$ echo 1 > foo; stat foo; echo 2 > foo; stat foo
File: foo
Size: 2 Blocks: 8 IO Block: 4096 regular file
Device: 801h/2049d Inode: 3546179 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ builder) Gid: ( 1000/ builder)
Access: 2018-10-29 22:14:10.894942036 +0000
Modify: 2018-10-29 22:14:10.894942036 +0000
Change: 2018-10-29 22:14:10.894942036 +0000
Birth: -
File: foo
Size: 2 Blocks: 8 IO Block: 4096 regular file
Device: 801h/2049d Inode: 3546179 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ builder) Gid: ( 1000/ builder)
Access: 2018-10-29 22:14:10.894942036 +0000
Modify: 2018-10-29 22:14:10.898942036 +0000
Change: 2018-10-29 22:14:10.898942036 +0000
Birth: -
I'm seeing this in Linux VMs; it doesn't happen on my laptop. I've also
not experienced the intermittent test suite failures on my laptop.
So, I hope that this small delay will avoid the problem.
Update: I didn't, indeed I then reproduced the same failure on my
laptop, so it must be due to something else. But keeping this change anyway
since not needing to worry about lowish-resolution mtime in the test suite seems
worthwhile.
