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.
$ hgcommit() {
> hg commit -u user "$@"
> }
$ hg init clhead
$ cd clhead
$ touch foo && hg add && hgcommit -m 'foo'
adding foo
$ touch bar && hg add && hgcommit -m 'bar'
adding bar
$ touch baz && hg add && hgcommit -m 'baz'
adding baz
$ echo "flub" > foo
$ hgcommit -m "flub"
$ echo "nub" > foo
$ hgcommit -m "nub"
$ hg up -C 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo "c1" > c1
$ hg add c1
$ hgcommit -m "c1"
created new head
$ echo "c2" > c1
$ hgcommit -m "c2"
$ hg up -C 2
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo "d1" > d1
$ hg add d1
$ hgcommit -m "d1"
created new head
$ echo "d2" > d1
$ hgcommit -m "d2"
$ hg tag -l good
fail with three heads
$ hg up -C good
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg merge
abort: branch 'default' has 3 heads - please merge with an explicit rev
(run 'hg heads .' to see heads)
[255]
close one of the heads
$ hg up -C 6
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hgcommit -m 'close this head' --close-branch
succeed with two open heads
$ hg up -C good
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg up -C good
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg merge
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hgcommit -m 'merged heads'
hg update -C 8
$ hg update -C 8
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
hg branch some-branch
$ hg branch some-branch
marked working directory as branch some-branch
(branches are permanent and global, did you want a bookmark?)
hg commit
$ hgcommit -m 'started some-branch'
hg commit --close-branch
$ hgcommit --close-branch -m 'closed some-branch'
hg update default
$ hg update default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
hg merge some-branch
$ hg merge some-branch
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
hg commit (no reopening of some-branch)
$ hgcommit -m 'merge with closed branch'
$ cd ..