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.
====================================
Testing head checking code: Case A-6
====================================
Mercurial checks for the introduction of new heads on push. Evolution comes
into play to detect if existing branches on the server are being replaced by
some of the new one we push.
This case is part of a series of tests checking this behavior.
Category A: simple case involving a branch being superceeded by another.
TestCase 6: multi-changeset branch, split on multiple other, (base on its own branch), same number of head
.. old-state:
..
.. * 2 branch (1-changeset, and 2-changesets)
..
.. new-state:
..
.. * 1 new branch superceeding the base of the old-2-changesets-branch,
.. * 1 new changesets on the old-1-changeset-branch superceeding the head of the other
..
.. expected-result:
..
.. * push allowed
..
.. graph-summary:
..
.. B'◔⇢ø B
.. | |
.. A | ø⇠◔ A'
.. | |/
.. C ● |
.. \|
.. ●
$ . $TESTDIR/testlib/push-checkheads-util.sh
Test setup
----------
$ mkdir A6
$ cd A6
$ setuprepos
creating basic server and client repo
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd server
$ mkcommit B0
$ hg up 0
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ mkcommit C0
created new head
$ cd ../client
$ hg pull
pulling from $TESTTMP/A6/server
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 2 files (+1 heads)
new changesets d73caddc5533:0f88766e02d6 (2 drafts)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg up 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ mkcommit A1
created new head
$ hg up 'desc(C0)'
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ mkcommit B1
$ hg debugobsolete `getid "desc(A0)" ` `getid "desc(A1)"`
obsoleted 1 changesets
1 new orphan changesets
$ hg debugobsolete `getid "desc(B0)" ` `getid "desc(B1)"`
obsoleted 1 changesets
$ hg log -G --hidden
@ d70a1f75a020 (draft): B1
|
| o f6082bc4ffef (draft): A1
| |
o | 0f88766e02d6 (draft): C0
|/
| x d73caddc5533 (draft): B0
| |
| x 8aaa48160adc (draft): A0
|/
o 1e4be0697311 (public): root
Actual testing
--------------
$ hg push
pushing to $TESTTMP/A6/server
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 2 files (+1 heads)
2 new obsolescence markers
obsoleted 2 changesets
$ cd ../..