tests/test-extensions-afterloaded.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.

Test the extensions.afterloaded() function

  $ cat > foo.py <<EOF
  > from mercurial import extensions
  > def uisetup(ui):
  >     ui.write(b"foo.uisetup\\n")
  >     ui.flush()
  >     def bar_loaded(loaded):
  >         ui.write(b"foo: bar loaded: %r\\n" % (loaded,))
  >         ui.flush()
  >     extensions.afterloaded(b'bar', bar_loaded)
  > EOF
  $ cat > bar.py <<EOF
  > def uisetup(ui):
  >     ui.write(b"bar.uisetup\\n")
  >     ui.flush()
  > EOF
  $ basepath=`pwd`

  $ hg init basic
  $ cd basic
  $ echo foo > file
  $ hg add file
  $ hg commit -m 'add file'

  $ echo '[extensions]' >> .hg/hgrc
  $ echo "foo = $basepath/foo.py" >> .hg/hgrc
  $ echo "bar = $basepath/bar.py" >> .hg/hgrc
  $ hg log -r. -T'{rev}\n'
  foo.uisetup
  foo: bar loaded: True
  bar.uisetup
  0

Test afterloaded with the opposite extension load order

  $ cd ..
  $ hg init basic_reverse
  $ cd basic_reverse
  $ echo foo > file
  $ hg add file
  $ hg commit -m 'add file'

  $ echo '[extensions]' >> .hg/hgrc
  $ echo "bar = $basepath/bar.py" >> .hg/hgrc
  $ echo "foo = $basepath/foo.py" >> .hg/hgrc
  $ hg log -r. -T'{rev}\n'
  bar.uisetup
  foo.uisetup
  foo: bar loaded: True
  0

Test the extensions.afterloaded() function when the requested extension is not
loaded

  $ cd ..
  $ hg init notloaded
  $ cd notloaded
  $ echo foo > file
  $ hg add file
  $ hg commit -m 'add file'

  $ echo '[extensions]' >> .hg/hgrc
  $ echo "foo = $basepath/foo.py" >> .hg/hgrc
  $ hg log -r. -T'{rev}\n'
  foo.uisetup
  foo: bar loaded: False
  0

Test the extensions.afterloaded() function when the requested extension is not
configured but fails the minimum version check

  $ cd ..
  $ cat > minvers.py <<EOF
  > minimumhgversion = b'9999.9999'
  > def uisetup(ui):
  >     ui.write(b"minvers.uisetup\\n")
  >     ui.flush()
  > EOF
  $ hg init minversion
  $ cd minversion
  $ echo foo > file
  $ hg add file
  $ hg commit -m 'add file'

  $ echo '[extensions]' >> .hg/hgrc
  $ echo "foo = $basepath/foo.py" >> .hg/hgrc
  $ echo "bar = $basepath/minvers.py" >> .hg/hgrc
  $ hg log -r. -T'{rev}\n'
  (third party extension bar requires version 9999.9999 or newer of Mercurial (current: *); disabling) (glob)
  foo.uisetup
  foo: bar loaded: False
  0

Test the extensions.afterloaded() function when the requested extension is not
configured but fails the minimum version check, using the opposite load order
for the two extensions.

  $ cd ..
  $ hg init minversion_reverse
  $ cd minversion_reverse
  $ echo foo > file
  $ hg add file
  $ hg commit -m 'add file'

  $ echo '[extensions]' >> .hg/hgrc
  $ echo "bar = $basepath/minvers.py" >> .hg/hgrc
  $ echo "foo = $basepath/foo.py" >> .hg/hgrc
  $ hg log -r. -T'{rev}\n'
  (third party extension bar requires version 9999.9999 or newer of Mercurial (current: *); disabling) (glob)
  foo.uisetup
  foo: bar loaded: False
  0