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diff --git a/Documentation/gitsubmodules.txt b/Documentation/gitsubmodules.txt new file mode 100644 index 0000000000..f9f4e65c9e --- /dev/null +++ b/Documentation/gitsubmodules.txt @@ -0,0 +1,284 @@ +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 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: + +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 Git's 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. + 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. + +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 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. + + * 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 while paying attention +to the `.gitignore` file of the submodule. ++ +The submodule's `$GIT_DIR/config` file would come into play when running +`git push --recurse-submodules=check` in the superproject, as this would +check if the submodule has any changes not published to any remote. The +remotes are configured in the submodule as usual in the `$GIT_DIR/config` +file. + + * The configuration file `$GIT_DIR/config` in the superproject. + Git only recurses into active submodules (see "ACTIVE SUBMODULES" + section below). ++ +If the submodule is not yet initialized, then the configuration +inside the submodule does not exist yet, so where to +obtain the submodule from is configured here for example. + + * The `.gitmodules` file inside the superproject. A project usually + uses this file to suggest defaults for the upstream collection + of repositories for the mapping that is required between a + submodule's name and its path. ++ +This file mainly serves as the mapping between the name and path of submodules +in the superproject, such that the submodule's Git directory can be +located. ++ +If the submodule has never been initialized, this is the only place +where submodule configuration is found. It serves as the last fallback +to specify where to obtain the submodule from. + +FORMS +----- + +Submodules can take the following forms: + + * The basic form described in DESCRIPTION with a Git directory, +a working directory, a `gitlink`, and a `.gitmodules` entry. + + * "Old-form" submodule: A working directory with an embedded +`.git` directory, and the tracking `gitlink` and `.gitmodules` entry in +the superproject. This is typically found in repositories generated +using older versions of Git. ++ +It is possible to construct these old form repositories manually. ++ +When deinitialized or deleted (see below), the submodule's Git +directory is automatically moved to `$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>/`. + +ACTIVE SUBMODULES +----------------- + +A submodule is considered active, + + 1. if `submodule.<name>.active` is set to `true` ++ +or + + 2. if the submodule's path matches the pathspec in `submodule.active` ++ +or + + 3. 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 (1) and 'baz' due to (3). 'foo' is inactive because +(1) takes precedence over (3) + +Note that (3) is a historical artefact and will be ignored if the +(1) and (2) 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 +---------------------------------- + + # 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 (note that 'submodule.recurse' also +affects other git commands, see linkgit:git-config[1] for a complete list). + + +SEE ALSO +-------- +linkgit:git-submodule[1], linkgit:gitmodules[5]. + +GIT +--- +Part of the linkgit:git[1] suite |