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Merge branch 'sb/submodule-doc'

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Doc update.

* sb/submodule-doc:
  submodules: overhaul documentation
This commit is contained in:
Junio C Hamano 2017-07-12 15:18:21 -07:00
commit b5fe65fe93
4 changed files with 234 additions and 36 deletions
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1
Documentation/Makefile
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@ -31,6 +31,7 @@ MAN7_TXT += giteveryday.txt
MAN7_TXT += gitglossary.txt
MAN7_TXT += gitnamespaces.txt
MAN7_TXT += gitrevisions.txt
MAN7_TXT += gitsubmodules.txt
MAN7_TXT += gittutorial-2.txt
MAN7_TXT += gittutorial.txt
MAN7_TXT += gitworkflows.txt

4
Documentation/git-rm.txt
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@ -153,8 +153,8 @@ Ignored files are deemed expendable and won't stop a submodule's work
tree from being removed.
If you only want to remove the local checkout of a submodule from your
work tree without committing the removal,
use linkgit:git-submodule[1] `deinit` instead.
work tree without committing the removal, use linkgit:git-submodule[1] `deinit`
instead. Also see linkgit:gitsubmodules[7] for details on submodule removal.
EXAMPLES
--------

44
Documentation/git-submodule.txt
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@ -24,37 +24,7 @@ DESCRIPTION
-----------
Inspects, updates and manages submodules.
A submodule allows you to keep another Git repository in a subdirectory
of your repository. The other repository has its own history, which does not
interfere with the history of the current repository. This can be used to
have external dependencies such as third party libraries for example.
When cloning or pulling a repository containing submodules however,
these will not be checked out by default; the 'init' and 'update'
subcommands will maintain submodules checked out and at
appropriate revision in your working tree.
Submodules are composed from a so-called `gitlink` tree entry
in the main repository that refers to a particular commit object
within the inner repository that is completely separate.
A record in the `.gitmodules` (see linkgit:gitmodules[5]) file at the
root of the source tree assigns a logical name to the submodule and
describes the default URL the submodule shall be cloned from.
The logical name can be used for overriding this URL within your
local repository configuration (see 'submodule init').
Submodules are not to be confused with remotes, which are other
repositories of the same project; submodules are meant for
different projects you would like to make part of your source tree,
while the history of the two projects still stays completely
independent and you cannot modify the contents of the submodule
from within the main project.
If you want to merge the project histories and want to treat the
aggregated whole as a single project from then on, you may want to
add a remote for the other project and use the 'subtree' merge strategy,
instead of treating the other project as a submodule. Directories
that come from both projects can be cloned and checked out as a whole
if you choose to go that route.
For more information about submodules, see linkgit:gitsubmodules[7].
COMMANDS
--------
@ -142,15 +112,17 @@ deinit [-f|--force] (--all|[--] <path>...)::
tree. Further calls to `git submodule update`, `git submodule foreach`
and `git submodule sync` will skip any unregistered submodules until
they are initialized again, so use this command if you don't want to
have a local checkout of the submodule in your working tree anymore. If
you really want to remove a submodule from the repository and commit
that use linkgit:git-rm[1] instead.
have a local checkout of the submodule in your working tree anymore.
+
When the command is run without pathspec, it errors out,
instead of deinit-ing everything, to prevent mistakes.
+
If `--force` is specified, the submodule's working tree will
be removed even if it contains local modifications.
+
If you really want to remove a submodule from the repository and commit
that use linkgit:git-rm[1] instead. See linkgit:gitsubmodules[7] for removal
options.
update [--init] [--remote] [-N|--no-fetch] [--[no-]recommend-shallow] [-f|--force] [--checkout|--rebase|--merge] [--reference <repository>] [--depth <depth>] [--recursive] [--jobs <n>] [--] [<path>...]::
+
@ -428,6 +400,10 @@ This file should be formatted in the same way as `$GIT_DIR/config`. The key
to each submodule url is "submodule.$name.url". See linkgit:gitmodules[5]
for details.
SEE ALSO
--------
linkgit:gitsubmodules[7], linkgit:gitmodules[5].
GIT
---
Part of the linkgit:git[1] suite

221
Documentation/gitsubmodules.txt Normal file
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@ -0,0 +1,221 @@
gitsubmodules(7)
================
NAME
----
gitsubmodules - mounting one repository inside another
SYNOPSIS
--------
.gitmodules, $GIT_DIR/config
------------------
git submodule
git <command> --recurse-submodules
------------------
DESCRIPTION
-----------
A submodule is a repository embedded inside another repository.
The submodule has its own history; the repository it is embedded
in is called a superproject.
On the filesystem, a submodule usually (but not always - see FORMS below)
consists of (i) a Git directory located under the `$GIT_DIR/modules/`
directory of its superproject, (ii) a working directory inside the
superproject's working directory, and a `.git` file at the root of
the submodule’s working directory pointing to (i).
Assuming the submodule has a Git directory at `$GIT_DIR/modules/foo/`
and a working directory at `path/to/bar/`, the superproject tracks the
submodule via a `gitlink` entry in the tree at `path/to/bar` and an entry
in its `.gitmodules` file (see linkgit:gitmodules[5]) of the form
`submodule.foo.path = path/to/bar`.
The `gitlink` entry contains the object name of the commit that the
superproject expects the submodule’s working directory to be at.
The section `submodule.foo.*` in the `.gitmodules` file gives additional
hints to Gits porcelain layer such as where to obtain the submodule via
the `submodule.foo.url` setting.
Submodules can be used for at least two different use cases:
1. Using another project while maintaining independent history.
Submodules allow you to contain the working tree of another project
within your own working tree while keeping the history of both
projects separate. Also, since submodules are fixed to an arbitrary
version, the other project can be independently developed without
affecting the superproject, allowing the superproject project to
fix itself to new versions only when desired.
2. Splitting a (logically single) project into multiple
repositories and tying them back together. This can be used to
overcome current limitations of Gits implementation to have
finer grained access:
* Size of the git repository:
In its current form Git scales up poorly for large repositories containing
content that is not compressed by delta computation between trees.
However you can also use submodules to e.g. hold large binary assets
and these repositories are then shallowly cloned such that you do not
have a large history locally.
* Transfer size:
In its current form Git requires the whole working tree present. It
does not allow partial trees to be transferred in fetch or clone.
* Access control:
By restricting user access to submodules, this can be used to implement
read/write policies for different users.
The configuration of submodules
-------------------------------
Submodule operations can be configured using the following mechanisms
(from highest to lowest precedence):
* The command line for those commands that support taking submodule specs.
Most commands have a boolean flag '--recurse-submodules' whether to
recurse into submodules. Examples are `ls-files` or `checkout`.
Some commands take enums, such as `fetch` and `push`, where you can
specify how submodules are affected.
* The configuration inside the submodule. This includes `$GIT_DIR/config`
in the submodule, but also settings in the tree such as a `.gitattributes`
or `.gitignore` files that specify behavior of commands inside the
submodule.
+
For example an effect from the submodule's `.gitignore` file
would be observed when you run `git status --ignore-submodules=none` in
the superproject. This collects information from the submodule's working
directory by running `status` in the submodule, which does pay attention
to its `.gitignore` file.
+
The submodule's `$GIT_DIR/config` file would come into play when running
`git push --recurse-submodules=check` in the superproject, as this would
check if the submodule has any changes not published to any remote. The
remotes are configured in the submodule as usual in the `$GIT_DIR/config`
file.
* The configuration file `$GIT_DIR/config` in the superproject.
Typical configuration at this place is controlling if a submodule
is recursed into at all via the `active` flag for example.
+
If the submodule is not yet initialized, then the configuration
inside the submodule does not exist yet, so configuration where to
obtain the submodule from is configured here for example.
* the `.gitmodules` file inside the superproject. Additionally to the
required mapping between submodule's name and path, a project usually
uses this file to suggest defaults for the upstream collection
of repositories.
+
This file mainly serves as the mapping between name and path in
the superproject, such that the submodule's git directory can be
located.
+
If the submodule has never been initialized, this is the only place
where submodule configuration is found. It serves as the last fallback
to specify where to obtain the submodule from.
FORMS
-----
Submodules can take the following forms:
* The basic form described in DESCRIPTION with a Git directory,
a working directory, a `gitlink`, and a `.gitmodules` entry.
* "Old-form" submodule: A working directory with an embedded
`.git` directory, and the tracking `gitlink` and `.gitmodules` entry in
the superproject. This is typically found in repositories generated
using older versions of Git.
+
It is possible to construct these old form repositories manually.
+
When deinitialized or deleted (see below), the submodule’s Git
directory is automatically moved to `$GIT_DIR/modules/<name>/`
of the superproject.
* Deinitialized submodule: A `gitlink`, and a `.gitmodules` entry,
but no submodule working directory. The submodule’s git directory
may be there as after deinitializing the git directory is kept around.
The directory which is supposed to be the working directory is empty instead.
+
A submodule can be deinitialized by running `git submodule deinit`.
Besides emptying the working directory, this command only modifies
the superproject’s `$GIT_DIR/config` file, so the superproject’s history
is not affected. This can be undone using `git submodule init`.
* Deleted submodule: A submodule can be deleted by running
`git rm <submodule path> && git commit`. This can be undone
using `git revert`.
+
The deletion removes the superproject’s tracking data, which are
both the `gitlink` entry and the section in the `.gitmodules` file.
The submodule’s working directory is removed from the file
system, but the Git directory is kept around as it to make it
possible to checkout past commits without requiring fetching
from another repository.
+
To completely remove a submodule, manually delete
`$GIT_DIR/modules/<name>/`.
Workflow for a third party library
----------------------------------
# add a submodule
git submodule add <url> <path>
# occasionally update the submodule to a new version:
git -C <path> checkout <new version>
git add <path>
git commit -m "update submodule to new version"
# See the list of submodules in a superproject
git submodule status
# See FORMS on removing submodules
Workflow for an artificially split repo
--------------------------------------
# Enable recursion for relevant commands, such that
# regular commands recurse into submodules by default
git config --global submodule.recurse true
# Unlike the other commands below clone still needs
# its own recurse flag:
git clone --recurse <URL> <directory>
cd <directory>
# Get to know the code:
git grep foo
git ls-files
# Get new code
git fetch
git pull --rebase
# change worktree
git checkout
git reset
Implementation details
----------------------
When cloning or pulling a repository containing submodules the submodules
will not be checked out by default; You can instruct 'clone' to recurse
into submodules. The 'init' and 'update' subcommands of 'git submodule'
will maintain submodules checked out and at an appropriate revision in
your working tree. Alternatively you can set 'submodule.recurse' to have
'checkout' recursing into submodules.
SEE ALSO
--------
linkgit:git-submodule[1], linkgit:gitmodules[5].
GIT
---
Part of the linkgit:git[1] suite