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posix: always seek to EOF when opening a file in append mode...
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.
Kevin Bullock - - Load All Authors

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r35187:aef2b98d merge default
r43163:97ada9b8 5.0.2 stable
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environment.txt
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HG
Path to the 'hg' executable, automatically passed when running
hooks, extensions or external tools. If unset or empty, this is
the hg executable's name if it's frozen, or an executable named
'hg' (with %PATHEXT% [defaulting to COM/EXE/BAT/CMD] extensions on
Windows) is searched.
HGEDITOR
This is the name of the editor to run when committing. See EDITOR.
(deprecated, see :hg:`help config.ui.editor`)
HGENCODING
This overrides the default locale setting detected by Mercurial.
This setting is used to convert data including usernames,
changeset descriptions, tag names, and branches. This setting can
be overridden with the --encoding command-line option.
HGENCODINGMODE
This sets Mercurial's behavior for handling unknown characters
while transcoding user input. The default is "strict", which
causes Mercurial to abort if it can't map a character. Other
settings include "replace", which replaces unknown characters, and
"ignore", which drops them. This setting can be overridden with
the --encodingmode command-line option.
HGENCODINGAMBIGUOUS
This sets Mercurial's behavior for handling characters with
"ambiguous" widths like accented Latin characters with East Asian
fonts. By default, Mercurial assumes ambiguous characters are
narrow, set this variable to "wide" if such characters cause
formatting problems.
HGMERGE
An executable to use for resolving merge conflicts. The program
will be executed with three arguments: local file, remote file,
ancestor file.
(deprecated, see :hg:`help config.ui.merge`)
HGRCPATH
A list of files or directories to search for configuration
files. Item separator is ":" on Unix, ";" on Windows. If HGRCPATH
is not set, platform default search path is used. If empty, only
the .hg/hgrc from the current repository is read.
For each element in HGRCPATH:
- if it's a directory, all files ending with .rc are added
- otherwise, the file itself will be added
HGPLAIN
When set, this disables any configuration settings that might
change Mercurial's default output. This includes encoding,
defaults, verbose mode, debug mode, quiet mode, tracebacks, and
localization. This can be useful when scripting against Mercurial
in the face of existing user configuration.
In addition to the features disabled by ``HGPLAIN=``, the following
values can be specified to adjust behavior:
``+strictflags``
Restrict parsing of command line flags.
Equivalent options set via command line flags or environment
variables are not overridden.
See :hg:`help scripting` for details.
HGPLAINEXCEPT
This is a comma-separated list of features to preserve when
HGPLAIN is enabled. Currently the following values are supported:
``alias``
Don't remove aliases.
``color``
Don't disable colored output.
``i18n``
Preserve internationalization.
``revsetalias``
Don't remove revset aliases.
``templatealias``
Don't remove template aliases.
``progress``
Don't hide progress output.
Setting HGPLAINEXCEPT to anything (even an empty string) will
enable plain mode.
HGUSER
This is the string used as the author of a commit. If not set,
available values will be considered in this order:
- HGUSER (deprecated)
- configuration files from the HGRCPATH
- EMAIL
- interactive prompt
- LOGNAME (with ``@hostname`` appended)
(deprecated, see :hg:`help config.ui.username`)
EMAIL
May be used as the author of a commit; see HGUSER.
LOGNAME
May be used as the author of a commit; see HGUSER.
VISUAL
This is the name of the editor to use when committing. See EDITOR.
EDITOR
Sometimes Mercurial needs to open a text file in an editor for a
user to modify, for example when writing commit messages. The
editor it uses is determined by looking at the environment
variables HGEDITOR, VISUAL and EDITOR, in that order. The first
non-empty one is chosen. If all of them are empty, the editor
defaults to 'vi'.
PYTHONPATH
This is used by Python to find imported modules and may need to be
set appropriately if this Mercurial is not installed system-wide.