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.
$ addcommit () {
> echo $1 > $1
> hg add $1
> hg commit -d "${2} 0" -m $1
> }
$ commit () {
> hg commit -d "${2} 0" -m $1
> }
$ hg init a
$ cd a
$ addcommit "A" 0
$ addcommit "B" 1
$ echo "C" >> A
$ commit "C" 2
$ hg update -C 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo "D" >> A
$ commit "D" 3
created new head
State before the merge
$ hg status
$ hg id
e45016d2b3d3 tip
$ hg summary
parent: 3:e45016d2b3d3 tip
D
branch: default
commit: (clean)
update: 2 new changesets, 2 branch heads (merge)
phases: 4 draft
Testing the abort functionality first in case of conflicts
$ hg merge --abort
abort: no merge in progress
[255]
$ hg merge
merging A
warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
1 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
[1]
$ hg merge --abort e4501
abort: cannot specify a node with --abort
[255]
$ hg merge --abort --rev e4501
abort: cannot specify both --rev and --abort
[255]
$ hg merge --abort
aborting the merge, updating back to e45016d2b3d3
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
Checking that we got back in the same state
$ hg status
? A.orig
$ hg id
e45016d2b3d3 tip
$ hg summary
parent: 3:e45016d2b3d3 tip
D
branch: default
commit: 1 unknown (clean)
update: 2 new changesets, 2 branch heads (merge)
phases: 4 draft
Merging a conflict araises
$ hg merge
merging A
warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
1 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
[1]
Correct the conflict without marking the file as resolved
$ echo "ABCD" > A
$ hg commit -m "Merged"
abort: unresolved merge conflicts (see 'hg help resolve')
[255]
Mark the conflict as resolved and commit
$ hg resolve -m A
(no more unresolved files)
$ hg commit -m "Merged"
Test that if a file is removed but not marked resolved, the commit still fails
(issue4972)
$ hg up ".^"
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg merge 2
merging A
warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
1 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
[1]
$ hg rm --force A
$ hg commit -m merged
abort: unresolved merge conflicts (see 'hg help resolve')
[255]
$ hg resolve -ma
(no more unresolved files)
$ hg commit -m merged
created new head
Testing the abort functionality in case of no conflicts
$ hg update -C 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ addcommit "E" 4
created new head
$ hg id
68352a18a7c4 tip
$ hg merge -r 4
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg merge --preview --abort
abort: cannot specify --preview with --abort
[255]
$ hg merge --abort
aborting the merge, updating back to 68352a18a7c4
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg id
68352a18a7c4 tip
$ cd ..