Mercurial > hg
view tests/test-hgk.t @ 42562:97ada9b8d51b stable 5.0.2
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.
author | Augie Fackler <augie@google.com> |
---|---|
date | Mon, 08 Jul 2019 13:12:20 -0400 |
parents | 5fb1fc2e1281 |
children |
line wrap: on
line source
Minimal hgk check $ echo "[extensions]" >> $HGRCPATH $ echo "hgk=" >> $HGRCPATH $ hg init repo $ cd repo $ echo a > a $ hg ci -Am adda adding a $ hg debug-cat-file commit 0 tree a0c8bcbbb45c parent 000000000000 author test 0 0 revision 0 branch default phase draft adda $ echo b > b $ hg ci -Am addb adding b $ hg log -T '{node}\n' 102a90ea7b4a3361e4082ed620918c261189a36a 07f4944404050f47db2e5c5071e0e84e7a27bba9 $ hg debug-diff-tree 07f494440405 102a90ea7b4a :000000 100664 000000000000 1e88685f5dde N b b $ hg debug-diff-tree 07f494440405 102a90ea7b4a --patch diff --git a/b b/b new file mode 100644 --- /dev/null +++ b/b @@ -0,0 +1,1 @@ +b Ensure that diff-tree output isn't affected by diffopts $ hg --config diff.noprefix=True debug-diff-tree 07f494440405 102a90ea7b4a :000000 100664 000000000000 1e88685f5dde N b b $ hg --config diff.noprefix=True debug-diff-tree --patch 07f494440405 102a90ea7b4a diff --git a/b b/b new file mode 100644 --- /dev/null +++ b/b @@ -0,0 +1,1 @@ +b $ cd ..