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 >> $HGRCPATH <<EOF
> [extensions]
> convert=
> EOF
Prepare orig repo
$ hg init orig
$ cd orig
$ echo foo > foo
$ HGUSER='user name' hg ci -qAm 'foo'
$ cd ..
Explicit --authors
$ cat > authormap.txt <<EOF
> user name = Long User Name
>
> # comment
> this line is ignored
> EOF
$ hg convert --authors authormap.txt orig new
initializing destination new repository
ignoring bad line in author map file authormap.txt: this line is ignored
scanning source...
sorting...
converting...
0 foo
writing author map file $TESTTMP/new/.hg/authormap
$ cat new/.hg/authormap
user name=Long User Name
$ hg -Rnew log
changeset: 0:d89716e88087
tag: tip
user: Long User Name
date: Thu Jan 01 00:00:00 1970 +0000
summary: foo
$ rm -rf new
Implicit .hg/authormap
$ hg init new
$ mv authormap.txt new/.hg/authormap
$ hg convert orig new
ignoring bad line in author map file $TESTTMP/new/.hg/authormap: this line is ignored
scanning source...
sorting...
converting...
0 foo
$ hg -Rnew log
changeset: 0:d89716e88087
tag: tip
user: Long User Name
date: Thu Jan 01 00:00:00 1970 +0000
summary: foo