tests/test-archive-symlinks.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 symlink

  $ origdir=`pwd`

  $ hg init repo
  $ cd repo
  $ ln -s nothing dangling

avoid tar warnings about old timestamp

  $ hg ci -d '2000-01-01 00:00:00 +0000' -qAm 'add symlink'

  $ hg archive -t files ../archive
  $ hg archive -t tar -p tar ../archive.tar
  $ hg archive -t zip -p zip ../archive.zip

files

  $ cd "$origdir"
  $ cd archive
  $ readlink.py dangling
  dangling -> nothing

tar

  $ cd "$origdir"
  $ tar xf archive.tar
  $ cd tar
  $ readlink.py dangling
  dangling -> nothing

#if unziplinks
zip

  $ cd "$origdir"
  $ unzip archive.zip > /dev/null 2>&1
  $ cd zip
  $ readlink.py dangling
  dangling -> nothing
#endif

  $ cd ..