posix: always seek to EOF when opening a file in append mode
Python 3 already does this, so skip it there.
Consider the program:
#include <stdio.h>
int main() {
FILE *f = fopen("narf", "w");
fprintf(f, "narf\n");
fclose(f);
f = fopen("narf", "a");
printf("%ld\n", ftell(f));
fprintf(f, "troz\n");
printf("%ld\n", ftell(f));
return 0;
}
on macOS, FreeBSD, and Linux with glibc, this program prints
5
10
but on musl libc (Alpine Linux and probably others) this prints
0
10
By my reading of
https://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html
this is technically correct, specifically:
> Opening a file with append mode (a as the first character in the
> mode argument) shall cause all subsequent writes to the file to be
> forced to the then current end-of-file, regardless of intervening
> calls to fseek().
in other words, the file position doesn't really matter in append-mode
files, and we can't depend on it being at all meaningful unless we
perform a seek() before tell() after open(..., 'a'). Experimentally
after a .write() we can do a .tell() and it'll always be reasonable,
but I'm unclear from reading the specification if that's a smart thing
to rely on. This matches what we do on Windows and what Python 3 does
for free, so let's just be consistent. Thanks to Yuya for the idea.
$ cat <<EOF >> $HGRCPATH
> [extensions]
> convert =
> [convert]
> hg.tagsbranch = 0
> EOF
$ hg init source
$ cd source
$ echo a > a
$ hg ci -qAm adda
Add a merge with one parent in the same branch
$ echo a >> a
$ hg ci -qAm changea
$ hg up -qC 0
$ hg branch branch0
marked working directory as branch branch0
(branches are permanent and global, did you want a bookmark?)
$ echo b > b
$ hg ci -qAm addb
$ hg up -qC
$ hg merge default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -qm mergeab
$ hg tag -ql mergeab
$ cd ..
Miss perl... sometimes
$ cat > filter.py <<EOF
> from __future__ import absolute_import
> import re
> import sys
>
> r = re.compile(r'^(?:\d+|pulling from)')
> sys.stdout.writelines([l for l in sys.stdin if r.search(l)])
> EOF
convert
$ hg convert -v --config convert.hg.clonebranches=1 source dest |
> "$PYTHON" filter.py
3 adda
2 changea
1 addb
pulling from default into branch0
1 changesets found
0 mergeab
pulling from default into branch0
1 changesets found
Add a merge with both parents and child in different branches
$ cd source
$ hg branch branch1
marked working directory as branch branch1
$ echo a > file1
$ hg ci -qAm c1
$ hg up -qC mergeab
$ hg branch branch2
marked working directory as branch branch2
$ echo a > file2
$ hg ci -qAm c2
$ hg merge branch1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg branch branch3
marked working directory as branch branch3
$ hg ci -qAm c3
$ cd ..
incremental conversion
$ hg convert -v --config convert.hg.clonebranches=1 source dest |
> "$PYTHON" filter.py
2 c1
pulling from branch0 into branch1
4 changesets found
1 c2
pulling from branch0 into branch2
4 changesets found
0 c3
pulling from branch1 into branch3
5 changesets found
pulling from branch2 into branch3
1 changesets found