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]
> absorb=
> EOF
$ hg init repo1
$ cd repo1
Make some commits:
$ for i in 1 2 3; do
> echo $i >> a
> hg commit -A a -m "commit $i" -q
> done
absorb --edit-lines will run the editor if filename is provided:
$ hg absorb --edit-lines --apply-changes
nothing applied
[1]
$ HGEDITOR=cat hg absorb --edit-lines --apply-changes a
HG: editing a
HG: "y" means the line to the right exists in the changeset to the top
HG:
HG: /---- 4ec16f85269a commit 1
HG: |/--- 5c5f95224a50 commit 2
HG: ||/-- 43f0a75bede7 commit 3
HG: |||
yyy : 1
yy : 2
y : 3
nothing applied
[1]
Edit the file using --edit-lines:
$ cat > editortext << EOF
> y : a
> yy : b
> y : c
> yy : d
> y y : e
> y : f
> yyy : g
> EOF
$ HGEDITOR='cat editortext >' hg absorb -q --edit-lines --apply-changes a
$ hg cat -r 0 a
d
e
f
g
$ hg cat -r 1 a
b
c
d
g
$ hg cat -r 2 a
a
b
e
g