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 symlink
Create extension that can disable symlink support:
$ cat > nolink.py <<EOF
> from mercurial import extensions, util
> def setflags(orig, f, l, x):
> pass
> def checklink(orig, path):
> return False
> def extsetup(ui):
> extensions.wrapfunction(util, 'setflags', setflags)
> extensions.wrapfunction(util, 'checklink', checklink)
> EOF
$ hg init unix-repo
$ cd unix-repo
$ echo foo > a
$ ln -s a b
$ hg ci -Am0
adding a
adding b
$ cd ..
Simulate a checkout shared on NFS/Samba:
$ hg clone -q unix-repo shared
$ cd shared
$ rm b
$ echo foo > b
$ hg --config extensions.n=$TESTTMP/nolink.py status --debug
ignoring suspect symlink placeholder "b"
Make a clone using placeholders:
$ hg --config extensions.n=$TESTTMP/nolink.py clone . ../win-repo
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd ../win-repo
$ cat b
a (no-eol)
$ hg --config extensions.n=$TESTTMP/nolink.py st --debug
Empty placeholder:
$ rm b
$ touch b
$ hg --config extensions.n=$TESTTMP/nolink.py st --debug
ignoring suspect symlink placeholder "b"
Write binary data to the placeholder:
>>> open('b', 'w').write('this is a binary\0') and None
$ hg --config extensions.n=$TESTTMP/nolink.py st --debug
ignoring suspect symlink placeholder "b"
Write a long string to the placeholder:
>>> open('b', 'w').write('this' * 1000) and None
$ hg --config extensions.n=$TESTTMP/nolink.py st --debug
ignoring suspect symlink placeholder "b"
Commit shouldn't succeed:
$ hg --config extensions.n=$TESTTMP/nolink.py ci -m1
nothing changed
[1]
Write a valid string to the placeholder:
>>> open('b', 'w').write('this') and None
$ hg --config extensions.n=$TESTTMP/nolink.py st --debug
M b
$ hg --config extensions.n=$TESTTMP/nolink.py ci -m1
$ hg manifest tip --verbose
644 a
644 @ b
$ cd ..