consists of (i) a Git directory located under the `$GIT_DIR/modules/`
directory of its superproject, (ii) a working directory inside the
superproject's working directory, and a `.git` file at the root of
-the submodule’s working directory pointing to (i).
+the submodule's working directory pointing to (i).
Assuming the submodule has a Git directory at `$GIT_DIR/modules/foo/`
and a working directory at `path/to/bar/`, the superproject tracks the
`submodule.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.
+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.
+hints to Git's porcelain layer. For example, the `submodule.foo.url`
+setting specifies where to obtain the submodule.
Submodules can be used for at least two different use cases:
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
+ overcome current limitations of Git's implementation to have
finer grained access:
- * Size of the git repository:
+ * 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
+ For example, you can use submodules to hold large binary assets
+ and these repositories can be 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.
+ If the project you work on consists of multiple repositories tied
+ together as submodules in a superproject, you can avoid fetching the
+ working trees of the repositories you are not interested in.
* Access control:
By restricting user access to submodules, this can be used to implement
read/write policies for different users.
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`.
+ * The command line for those commands that support taking submodules
+ as part of their pathspecs. Most commands have a boolean flag
+ `--recurse-submodules` which specify whether to recurse into submodules.
+ Examples are `grep` and `checkout`.
Some commands take enums, such as `fetch` and `push`, where you can
specify how submodules are affected.
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.
+directory by running `status` in the submodule while paying attention
+to the `.gitignore` file of the submodule.
+
The submodule's `$GIT_DIR/config` file would come into play when running
`git push --recurse-submodules=check` in the superproject, as this would
file.
* The configuration file `$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.
+ Git only recurses into active submodules (see "ACTIVE SUBMODULES"
+ section below).
+
If the submodule is not yet initialized, then the configuration
-inside the submodule does not exist yet, so configuration where to
+inside the submodule does not exist yet, so 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
+ * The `.gitmodules` file inside the superproject. A project usually
uses this file to suggest defaults for the upstream collection
- of repositories.
+ of repositories for the mapping that is required between a
+ submodule's name and its path.
+
-This file mainly serves as the mapping between name and path in
-the superproject, such that the submodule's git directory can be
+This file mainly serves as the mapping between the name and path of submodules
+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
+
It is possible to construct these old form repositories manually.
+
-When deinitialized or deleted (see below), the submodule’s Git
+When deinitialized or deleted (see below), the submodule's Git
directory is automatically moved to `$GIT_DIR/modules/<name>/`
of the superproject.
* Deinitialized submodule: A `gitlink`, and a `.gitmodules` entry,
-but no submodule working directory. The submodule’s git directory
-may be there as after deinitializing the git directory is kept around.
+but no submodule working directory. The submodule's Git directory
+may be there as after deinitializing the Git directory is kept around.
The directory which is supposed to be the working directory is empty instead.
+
A submodule can be deinitialized by running `git submodule deinit`.
Besides emptying the working directory, this command only modifies
-the superproject’s `$GIT_DIR/config` file, so the superproject’s history
+the superproject's `$GIT_DIR/config` file, so the superproject's history
is not affected. This can be undone using `git submodule init`.
* Deleted submodule: A submodule can be deleted by running
`git rm <submodule path> && git commit`. This can be undone
using `git revert`.
+
-The deletion removes the superproject’s tracking data, which are
+The deletion removes the superproject's tracking data, which are
both the `gitlink` entry and the section in the `.gitmodules` file.
-The submodule’s working directory is removed from the file
+The submodule's working directory is removed from the file
system, but the Git directory is kept around as it to make it
possible to checkout past commits without requiring fetching
from another repository.
To completely remove a submodule, manually delete
`$GIT_DIR/modules/<name>/`.
+ACTIVE SUBMODULES
+-----------------
+
+A submodule is considered active,
+
+ (a) if `submodule.<name>.active` is set to `true`
+ or
+ (b) if the submodule's path matches the pathspec in `submodule.active`
+ or
+ (c) if `submodule.<name>.url` is set.
+
+and these are evaluated in this order.
+
+For example:
+
+ [submodule "foo"]
+ active = false
+ url = https://example.org/foo
+ [submodule "bar"]
+ active = true
+ url = https://example.org/bar
+ [submodule "baz"]
+ url = https://example.org/baz
+
+In the above config only the submodule 'bar' and 'baz' are active,
+'bar' due to (a) and 'baz' due to (c). 'foo' is inactive because
+(a) takes precedence over (c)
+
+Note that (c) is a historical artefact and will be ignored if the
+(a) and (b) specify that the submodule is not active. In other words,
+if we have a `submodule.<name>.active` set to `false` or if the
+submodule's path is excluded in the pathspec in `submodule.active`, the
+url doesn't matter whether it is present or not. This is illustrated in
+the example that follows.
+
+ [submodule "foo"]
+ active = true
+ url = https://example.org/foo
+ [submodule "bar"]
+ url = https://example.org/bar
+ [submodule "baz"]
+ url = https://example.org/baz
+ [submodule "bob"]
+ ignore = true
+ [submodule]
+ active = b*
+ active = :(exclude) baz
+
+In here all submodules except 'baz' (foo, bar, bob) are active.
+'foo' due to its own active flag and all the others due to the
+submodule active pathspec, which specifies that any submodule
+starting with 'b' except 'baz' are also active, regardless of the
+presence of the .url field.
+
Workflow for a third party library
----------------------------------