tests/test-remotefilelog-wireproto.t

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.

#require no-windows

  $ . "$TESTDIR/remotefilelog-library.sh"

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > server=True
  > EOF
  $ echo x > x
  $ hg commit -qAm x
  $ echo y >> x
  $ hg commit -qAm y
  $ echo z >> x
  $ hg commit -qAm z
  $ hg update 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo w >> x
  $ hg commit -qAm w

  $ cd ..

Shallow clone and activate getflogheads testing extension

  $ hgcloneshallow ssh://user@dummy/master shallow --noupdate
  streaming all changes
  2 files to transfer, 908 bytes of data
  transferred 908 bytes in * seconds (*/sec) (glob)
  searching for changes
  no changes found
  $ cd shallow

  $ cat >> .hg/hgrc <<EOF
  > [extensions]
  > getflogheads=$TESTDIR/remotefilelog-getflogheads.py
  > EOF

Get heads of a remotefilelog

  $ hg getflogheads x
  2797809ca5e9c2f307d82b1345e832f655fb99a2
  ca758b402ddc91e37e3113e1a97791b537e1b7bb

Get heads of a non-existing remotefilelog

  $ hg getflogheads y
  EMPTY