view mercurial/help/hg.1.txt @ 29375:fcaf20175b1b

demandimport: delay loading for "from a import b" with absolute_import

Before this patch, "from a import b" doesn't delay loading module "b",
if absolute_import is enabled, even though "from . import b" does.

For example:

  - it is assumed that extension X has "from P import M" for module M
    under package P with absolute_import feature

  - if importing module M is already delayed before loading extension
    X, loading module M in extension X is delayed until actually
    referring

    util, cmdutil, scmutil or so of Mercurial itself should be
    imported by "from . import M" style before loading extension X

  - otherwise, module M is loaded immediately at loading extension X,
    even if extension X itself isn't used at that "hg" command invocation

    Some minor modules (e.g. filemerge or so) of Mercurial itself
    aren't imported by "from . import M" style before loading
    extension X. And of course, external libraries aren't, too.

This might cause startup performance problem of hg command, because
many bundled extensions already enable absolute_import feature.

To delay loading module for "from a import b" with absolute_import
feature, this patch does below in "from a (or .a) import b" with
absolute_import case:

  1. import root module of "name" by system built-in __import__
     (referred as _origimport)

  2. recurse down the module chain for hierarchical "name"

     This logic can be shared with non absolute_import
     case. Therefore, this patch also centralizes it into chainmodules().

  3. and fall through to process elements in "fromlist" for the leaf
     module of "name"

     Processing elements in "fromlist" is executed in the code path
     after "if _pypy: .... else: ..." clause. Therefore, this patch
     replaces "if _pypy:" with "elif _pypy:" to share it.

At 4f1144c3c72b introducing original "work around" for "from a import
b" case, elements in "fromlist" were imported with "level=level". But
"level" might be grater than 1 (e.g. level=2 in "from .. import b"
case) at demandimport() invocation, and importing direct sub-module in
"fromlist" with level grater than 1 causes unexpected result.

IMHO, this seems main reason of "errors for unknown reason" described
in 4f1144c3c72b, and we don't have to worry about it, because this
issue was already fixed by 78d05778907b.

This is reason why this patch removes "errors for unknown reasons"
comment.

====
 hg
====

---------------------------------------
Mercurial source code management system
---------------------------------------

:Author:         Matt Mackall <[e-mail]>
:Organization:   Mercurial
:Manual section: 1
:Manual group:   Mercurial Manual

.. contents::
   :backlinks: top
   :class: htmlonly
   :depth: 1


Synopsis
""""""""
**hg** *command* [*option*]... [*argument*]...

Description
"""""""""""
The **hg** command provides a command line interface to the Mercurial
system.

Command Elements
""""""""""""""""

files...
    indicates one or more filename or relative path filenames; see
    `File Name Patterns`_ for information on pattern matching

path
    indicates a path on the local machine

revision
    indicates a changeset which can be specified as a changeset
    revision number, a tag, or a unique substring of the changeset
    hash value

repository path
    either the pathname of a local repository or the URI of a remote
    repository.

.. include:: hg.1.gendoc.txt

Files
"""""

``/etc/mercurial/hgrc``, ``$HOME/.hgrc``, ``.hg/hgrc``
    This file contains defaults and configuration. Values in
    ``.hg/hgrc`` override those in ``$HOME/.hgrc``, and these override
    settings made in the global ``/etc/mercurial/hgrc`` configuration.
    See |hgrc(5)|_ for details of the contents and format of these
    files.

``.hgignore``
    This file contains regular expressions (one per line) that
    describe file names that should be ignored by **hg**. For details,
    see |hgignore(5)|_.

``.hgsub``
    This file defines the locations of all subrepositories, and
    tells where the subrepository checkouts came from. For details, see
    :hg:`help subrepos`.

``.hgsubstate``
    This file is where Mercurial stores all nested repository states. *NB: This
    file should not be edited manually.*

``.hgtags``
    This file contains changeset hash values and text tag names (one
    of each separated by spaces) that correspond to tagged versions of
    the repository contents. The file content is encoded using UTF-8.

``.hg/last-message.txt``
    This file is used by :hg:`commit` to store a backup of the commit message
    in case the commit fails.

``.hg/localtags``
    This file can be used to define local tags which are not shared among
    repositories. The file format is the same as for ``.hgtags``, but it is
    encoded using the local system encoding.

Some commands (e.g. revert) produce backup files ending in ``.orig``,
if the ``.orig`` file already exists and is not tracked by Mercurial,
it will be overwritten.

Bugs
""""
Probably lots, please post them to the mailing list (see Resources_
below) when you find them.

See Also
""""""""
|hgignore(5)|_, |hgrc(5)|_

Author
""""""
Written by Matt Mackall <[e-mail]>

Resources
"""""""""
Main Web Site: https://mercurial-scm.org/

Source code repository: http://selenic.com/hg

Mailing list: http://selenic.com/mailman/listinfo/mercurial

Copying
"""""""
Copyright (C) 2005-2016 Matt Mackall.
Free use of this software is granted under the terms of the GNU General
Public License version 2 or any later version.

.. include:: common.txt