scmutil: add file object wrapper class to check ambiguity at closing
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 adds file object wrapper class checkambigatclosing to check
(and get rid of) ambiguity at closing. It is used by vfs in subsequent
patch.
This is a part of ExactCacheValidationPlan.
https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan
BTW, checkambigatclosing is tested in test-filecache.py, even though
it doesn't use filecache itself, because filecache assumes that file
stat ambiguity never occurs (and there is no another test-*.py related
to filecache).
Set up a repo
$ cat <<EOF >> $HGRCPATH
> [ui]
> interactive = true
> [extensions]
> record =
> EOF
$ hg init a
$ cd a
Record help
$ hg record -h
hg record [OPTION]... [FILE]...
interactively select changes to commit
If a list of files is omitted, all changes reported by 'hg status' will be
candidates for recording.
See 'hg help dates' for a list of formats valid for -d/--date.
You will be prompted for whether to record changes to each modified file,
and for files with multiple changes, for each change to use. For each
query, the following responses are possible:
y - record this change
n - skip this change
e - edit this change manually
s - skip remaining changes to this file
f - record remaining changes to this file
d - done, skip remaining changes and files
a - record all changes to all remaining files
q - quit, recording no changes
? - display help
This command is not available when committing a merge.
(use 'hg help -e record' to show help for the record extension)
options ([+] can be repeated):
-A --addremove mark new/missing files as added/removed before
committing
--close-branch mark a branch head as closed
--amend amend the parent of the working directory
-s --secret use the secret phase for committing
-e --edit invoke editor on commit messages
-I --include PATTERN [+] include names matching the given patterns
-X --exclude PATTERN [+] exclude names matching the given patterns
-m --message TEXT use text as commit message
-l --logfile FILE read commit message from file
-d --date DATE record the specified date as commit date
-u --user USER record the specified user as committer
-S --subrepos recurse into subrepositories
-w --ignore-all-space ignore white space when comparing lines
-b --ignore-space-change ignore changes in the amount of white space
-B --ignore-blank-lines ignore changes whose lines are all blank
(some details hidden, use --verbose to show complete help)
Select no files
$ touch empty-rw
$ hg add empty-rw
$ hg record empty-rw<<EOF
> n
> EOF
diff --git a/empty-rw b/empty-rw
new file mode 100644
examine changes to 'empty-rw'? [Ynesfdaq?] n
no changes to record
$ hg tip -p
changeset: -1:000000000000
tag: tip
user:
date: Thu Jan 01 00:00:00 1970 +0000