tests/test-narrow-update.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.

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

create full repo

  $ hg init master
  $ cd master
  $ echo init > init
  $ hg ci -Aqm 'initial'

  $ mkdir inside
  $ echo inside > inside/f1
  $ mkdir outside
  $ echo outside > outside/f1
  $ hg ci -Aqm 'add inside and outside'

  $ echo modified > inside/f1
  $ hg ci -qm 'modify inside'

  $ echo modified > outside/f1
  $ hg ci -qm 'modify outside'

  $ cd ..

  $ hg clone --narrow ssh://user@dummy/master narrow --include inside
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 4 changesets with 2 changes to 1 files
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow
  $ hg debugindex -c
     rev linkrev nodeid       p1           p2
       0       0 9958b1af2add 000000000000 000000000000
       1       1 2db4ce2a3bfe 9958b1af2add 000000000000
       2       2 0980ee31a742 2db4ce2a3bfe 000000000000
       3       3 4410145019b7 0980ee31a742 000000000000

  $ hg update -q 0

Can update to revision with changes inside

  $ hg update -q 'desc("add inside and outside")'
  $ hg update -q 'desc("modify inside")'
  $ find *
  inside
  inside/f1
  $ cat inside/f1
  modified

Can update to revision with changes outside

  $ hg update -q 'desc("modify outside")'
  $ find *
  inside
  inside/f1
  $ cat inside/f1
  modified

Can update with a deleted file inside

  $ hg rm inside/f1
  $ hg update -q 'desc("modify inside")'
  $ hg update -q 'desc("modify outside")'
  $ hg update -q 'desc("initial")'
  $ hg update -q 'desc("modify inside")'

Can update with a moved file inside

  $ hg mv inside/f1 inside/f2
  $ hg update -q 'desc("modify outside")'
  $ hg update -q 'desc("initial")'
  $ hg update -q 'desc("modify inside")'