mercurial/help/environment.txt

namespaces: let namespaces override singlenode() definition

Some namespaces have multiple nodes per name (meaning that their
namemap() returns multiple nodes). One such namespace is the "topics"
namespace (from the evolve repo). We also have our own internal
namespace at Google (for review units) that has multiple nodes per
name. These namespaces may not want to use the default "pick highest
revnum" resolution that we currently use when resolving a name to a
single node. As an example, they may decide that `hg co <name>` should
check out a commit that's last in some sense even if an earlier commit
had just been amended and thus had a higher revnum [1]. This patch
gives the namespace the option to continue to return multiple nodes
and to override how the best node is picked. Allowing namespaces to
override that may also be useful as an optimization (it may be cheaper
for the namespace to find just that node).

I have been arguing (in D3715) for using all the nodes returned from
namemap() when resolving the symbol to a revset, so e.g. `hg log -r
stable` would resolve to *all* nodes on stable, not just the one with
the highest revnum (except that I don't actually think we should
change it for the branch namespace because of BC). Most people seem
opposed to that. If we decide not to do it, I think we can deprecate
the namemap() function in favor of the new singlenode() (I find it
weird to have namespaces, like the branch namespace, where namemap()
isn't nodemap()'s inverse). I therefore think this patch makes sense
regardless of what we decide on that issue.


 [1] Actually, even the branch namespace would have wanted to override
     singlenode() if it had supported multiple nodes. That's because
     closes branch heads are mostly ignored, so "hg co default" will
     not check out the highest-revnum node if that's a closed head.

Differential Revision: https://phab.mercurial-scm.org/D3852

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.