view mercurial/help/environment.txt @ 28487:98d98a645e9d

changelog: add class to represent parsed changelog revisions

Currently, changelog entries are parsed into their respective
components at read time. Many operations are only interested
in a subset of fields of a changelog entry. The parsing and
storing of all the fields adds avoidable overhead.

This patch introduces the "changelogrevision" class. It takes
changelog raw text and exposes the parsed results as attributes.
The code for parsing changelog entries has been moved into its
construction function. changelog.read() has been modified to use
the new class internally while maintaining its existing API.
Future patches will make revision parsing lazy.

We implement the construction function of the new class with
__new__ instead of __init__ so we can use a named tuple to
represent the empty revision. This saves overhead and complexity
of coercing later versions of this class to represent an empty
instance.

While we are here, we add a method on changelog to obtain an
instance of the new type.

The overhead of constructing the new class regresses performance
of revsets accessing this data:

author(mpm)
0.896565
0.929984

desc(bug)
0.887169
0.935642 105%

date(2015)
0.878797
0.908094

extra(rebase_source)
0.865446
0.922624 106%

author(mpm) or author(greg)
1.801832
1.902112 105%

author(mpm) or desc(bug)
1.812438
1.860977

date(2015) or branch(default)
0.968276
1.005824

author(mpm) or desc(bug) or date(2015) or extra(rebase_source)
3.656193
3.743381

Once lazy parsing is implemented, these revsets will all be faster
than before. There is no performance change on revsets that do not
access this data. There /could/ be a performance regression on
operations that perform several changelog reads. However, I can't
think of anything outside of revsets and `hg log` (basically the
same as a revset) that would be impacted.

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, use configuration file)

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, use configuration file)

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.

    Equivalent options set via command line flags or environment
    variables are not overridden.

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.
    ``i18n``
        Preserve internationalization.
    ``revsetalias``
        Don't remove revset 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, use configuration file)

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.