tests/test-duplicateoptions.py

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.

from __future__ import absolute_import, print_function
import os
from mercurial import (
    commands,
    extensions,
    ui as uimod,
)

ignore = {b'highlight', b'win32text', b'factotum', b'beautifygraph'}

try:
    import sqlite3
    del sqlite3 # unused, just checking that import works
except ImportError:
    ignore.add(b'sqlitestore')

if os.name != 'nt':
    ignore.add(b'win32mbcs')

disabled = [ext for ext in extensions.disabled().keys() if ext not in ignore]

hgrc = open(os.environ["HGRCPATH"], 'wb')
hgrc.write(b'[extensions]\n')

for ext in disabled:
    hgrc.write(ext + b'=\n')

hgrc.close()

u = uimod.ui.load()
extensions.loadall(u)
extensions.populateui(u)

globalshort = set()
globallong = set()
for option in commands.globalopts:
    option[0] and globalshort.add(option[0])
    option[1] and globallong.add(option[1])

for cmd, entry in commands.table.items():
    seenshort = globalshort.copy()
    seenlong = globallong.copy()
    for option in entry[1]:
        if ((option[0] and option[0] in seenshort) or
            (option[1] and option[1] in seenlong)):
            print("command '" + cmd + "' has duplicate option " + str(option))
        seenshort.add(option[0])
        seenlong.add(option[1])