vfs: use checkambigatclosing in checkambig=True but atomictemp=False case
In Mercurial source tree, opening a file in "a"/"a+" mode like below
doesn't specify atomictemp=True for vfs, and this avoids file stat
ambiguity check by atomictempfile.
- writing changes out in revlog layer uses "a+" mode
- truncation in repair.strip() uses "a" mode
- truncation in transaction._playback() uses "a" mode
If steps below occurs at "the same time in sec", all of mtime, ctime
and size are same between (1) and (3).
1. append data to revlog-style file (and close transaction)
2. discard appended data by truncation (strip or rollback)
3. append same size but different data to revlog-style file again
Therefore, cache validation doesn't work after (3) as expected.
This patch uses checkambigatclosing in checkambig=True but
atomictemp=False case, to check (and get rid of) file stat ambiguity
at closing.
This is a part of ExactCacheValidationPlan.
https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan
Testing that hghave does not crash when checking features
$ hghave --test-features 2>/dev/null
Testing hghave extensibility for third party tools
$ cat > hghaveaddon.py <<EOF
> import hghave
> @hghave.check("custom", "custom hghave feature")
> def has_custom():
> return True
> EOF
(invocation via run-tests.py)
$ cat > test-hghaveaddon.t <<EOF
> #require custom
> $ echo foo
> foo
> EOF
$ run-tests.py $HGTEST_RUN_TESTS_PURE test-hghaveaddon.t
.
# Ran 1 tests, 0 skipped, 0 warned, 0 failed.
(invocation via command line)
$ unset TESTDIR
$ hghave custom
(terminate with exit code 2 at failure of importing hghaveaddon.py)
$ rm hghaveaddon.*
$ cat > hghaveaddon.py <<EOF
> importing this file should cause syntax error
> EOF
$ hghave custom
failed to import hghaveaddon.py from '.': invalid syntax (hghaveaddon.py, line 1)
[2]