Mercurial > hg
view tests/test-issue1175.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 | 3a7efcbdf288 |
children | 3df0bd706c40 |
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https://bz.mercurial-scm.org/1175 $ hg init $ touch a $ hg ci -Am0 adding a $ hg mv a a1 $ hg ci -m1 $ hg co 0 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg mv a a2 $ hg up note: possible conflict - a was renamed multiple times to: a1 a2 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ hg ci -m2 $ touch a $ hg ci -Am3 adding a $ hg mv a b $ hg ci -Am4 a $ hg ci --debug --traceback -Am5 b committing files: b warning: can't find ancestor for 'b' copied from 'a'! committing manifest committing changelog updating the branch cache committed changeset 5:83a687e8a97c80992ba385bbfd766be181bfb1d1 $ hg verify checking changesets checking manifests crosschecking files in changesets and manifests checking files checked 6 changesets with 4 changes to 4 files $ hg export --git tip # HG changeset patch # User test # Date 0 0 # Thu Jan 01 00:00:00 1970 +0000 # Node ID 83a687e8a97c80992ba385bbfd766be181bfb1d1 # Parent 1d1625283f71954f21d14c3d44d0ad3c019c597f 5 diff --git a/b b/b new file mode 100644 https://bz.mercurial-scm.org/show_bug.cgi?id=4476 $ hg init foo $ cd foo $ touch a && hg ci -Aqm a $ hg mv a b $ echo b1 >> b $ hg ci -Aqm b1 $ hg up 0 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg mv a b $ echo b2 >> b $ hg ci -Aqm b2 $ hg graft 1 grafting 1:5974126fad84 "b1" merging b warning: conflicts while merging b! (edit, then use 'hg resolve --mark') abort: unresolved conflicts, can't continue (use 'hg resolve' and 'hg graft --continue') [255] $ echo a > b $ echo b3 >> b $ hg resolve --mark b (no more unresolved files) continue: hg graft --continue $ hg graft --continue grafting 1:5974126fad84 "b1" warning: can't find ancestor for 'b' copied from 'a'! $ hg log -f b -T 'changeset: {rev}:{node|short}\nsummary: {desc}\n\n' changeset: 3:376d30ccffc0 summary: b1 changeset: 2:416baaa2e5e4 summary: b2 changeset: 0:3903775176ed summary: a