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.
#require no-windows
$ . "$TESTDIR/remotefilelog-library.sh"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > foo
$ echo y > bar
$ hg commit -qAm one
$ cd ..
# partial shallow clone
$ hg clone --shallow ssh://user@dummy/master shallow --noupdate --config remotefilelog.includepattern=foo
streaming all changes
3 files to transfer, 336 bytes of data
transferred 336 bytes in * seconds (*/sec) (glob)
searching for changes
no changes found
$ cat >> shallow/.hg/hgrc <<EOF
> [remotefilelog]
> cachepath=$PWD/hgcache
> debug=True
> includepattern=foo
> reponame = master
> [extensions]
> remotefilelog=
> EOF
$ ls shallow/.hg/store/data
bar.i
# update partial clone
$ cd shallow
$ hg update
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)
$ cat foo
x
$ cat bar
y
$ cd ..
# pull partial clone
$ cd master
$ echo a >> foo
$ echo b >> bar
$ hg commit -qm two
$ cd ../shallow
$ hg pull
pulling from ssh://user@dummy/master
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files
new changesets a9688f18cb91
(run 'hg update' to get a working copy)
$ hg update
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)
$ cat foo
x
a
$ cat bar
y
b
$ cd ..