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.
#!/usr/bin/env python
#
# Copyright 2014 Matt Mackall <mpm@selenic.com>
#
# A tool/hook to run basic sanity checks on commits/patches for
# submission to Mercurial. Install by adding the following to your
# .hg/hgrc:
#
# [hooks]
# pretxncommit = contrib/check-commit
#
# The hook can be temporarily bypassed with:
#
# $ BYPASS= hg commit
#
# See also: https://mercurial-scm.org/wiki/ContributingChanges
from __future__ import absolute_import, print_function
import os
import re
import sys
commitheader = r"^(?:# [^\n]*\n)*"
afterheader = commitheader + r"(?!#)"
beforepatch = afterheader + r"(?!\n(?!@@))"
errors = [
(beforepatch + r".*[(]bc[)]", "(BC) needs to be uppercase"),
(beforepatch + r".*[(]issue \d\d\d",
"no space allowed between issue and number"),
(beforepatch + r".*[(]bug(\d|\s)", "use (issueDDDD) instead of bug"),
(commitheader + r"# User [^@\n]+\n", "username is not an email address"),
(commitheader + r"(?!merge with )[^#]\S+[^:] ",
"summary line doesn't start with 'topic: '"),
(afterheader + r"[A-Z][a-z]\S+", "don't capitalize summary lines"),
(afterheader + r"^\S+: *[A-Z][a-z]\S+", "don't capitalize summary lines"),
(afterheader + r"\S*[^A-Za-z0-9-_]\S*: ",
"summary keyword should be most user-relevant one-word command or topic"),
(afterheader + r".*\.\s*\n", "don't add trailing period on summary line"),
(afterheader + r".{79,}", "summary line too long (limit is 78)"),
# Forbid "_" in function name.
#
# We skip the check for cffi related functions. They use names mapping the
# name of the C function. C function names may contain "_".
(r"\n\+[ \t]+def (?!cffi)[a-z]+_[a-z]",
"adds a function with foo_bar naming"),
]
word = re.compile(r'\S')
def nonempty(first, second):
if word.search(first):
return first
return second
def checkcommit(commit, node=None):
exitcode = 0
printed = node is None
hits = []
signtag = (afterheader +
r'Added (tag [^ ]+|signature) for changeset [a-f0-9]{12}')
if re.search(signtag, commit):
return 0
for exp, msg in errors:
for m in re.finditer(exp, commit):
end = m.end()
trailing = re.search(r'(\\n)+$', exp)
if trailing:
end -= len(trailing.group()) / 2
hits.append((end, exp, msg))
if hits:
hits.sort()
pos = 0
last = ''
for n, l in enumerate(commit.splitlines(True)):
pos += len(l)
while len(hits):
end, exp, msg = hits[0]
if pos < end:
break
if not printed:
printed = True
print("node: %s" % node)
print("%d: %s" % (n, msg))
print(" %s" % nonempty(l, last)[:-1])
if "BYPASS" not in os.environ:
exitcode = 1
del hits[0]
last = nonempty(l, last)
return exitcode
def readcommit(node):
return os.popen("hg export %s" % node).read()
if __name__ == "__main__":
exitcode = 0
node = os.environ.get("HG_NODE")
if node:
commit = readcommit(node)
exitcode = checkcommit(commit)
elif sys.argv[1:]:
for node in sys.argv[1:]:
exitcode |= checkcommit(readcommit(node), node)
else:
commit = sys.stdin.read()
exitcode = checkcommit(commit)
sys.exit(exitcode)