gclient is a tool for managing a modular checkout of source code from multiple source code repositories. It wraps underlying source code management commands to provide support for distributing tree updates, status commands, and diffs across multiple checked-out working directories.

The gclient script is controlled by a .gclient file at the top of a directory tree which will contain source code from multiple locations. A .gclient file is a Python script that defines a list of solutions with the following format:

solutions = [
  { "name"        : "src",
    "url"         : "https://chromium.googlesource.com/chromium/src.git",
    "custom_deps" : {
      # To use the trunk of a component instead of what's in DEPS:
      #"component": "https://github.com/luci/luci-go",
      # To exclude a component from your working copy:
      #"data/really_large_component": None,

A solution is a collection of component pieces of software that will be checked out in a specific directory layout for building together.

Each entry in the solutions list is defined by a Python dictionary that contains the following items:

  • name: The name of the directory in which the solution will be checked out.
  • url: The URL from which this solution will be checked out. gclient expects that the checked-out solution will contain a file named DEPS that in turn defines the specific pieces that must be checked out to create the working directory layout for building and developing the solution's software.
  • deps_file: A string containing just the filename (not a path) of the file in the solution dir to use as the list of dependencies. This tag is optional, and defaults to DEPS.
  • custom_deps: A dictionary containing optional custom overrides for entries in the solution's DEPS file. This can be used to have the local working directory not check out and update specific components, or to sync the local working-directory copy of a given component to a different specific revision, or a branch, or the head of a tree. It can also be used to append new entries that do not exist in the DEPS file.

Within each checked-out solution, gclient expects to find a file typically named DEPS (it actually uses the value of the deps_file key above) which defines the different component pieces of software that must be checked out for the solution. The DEPS file is a Python script that defines a dictionary named deps:

deps = {
  "src/outside": "https://outside-server/one/repo.git@12345677890123456778901234567789012345677890",
  "src/component": "https://dont-use-github.com/its/unreliable.git@0000000000000000000000000000000000000000",
  "src/relative": "/another/repo.git@aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",

Each item in the deps dictionary consists of a key-value pair. The key is the directory into which the component will be checked out, relative to the directory containing the .gclient file. The value is the URL from which that directory will be checked out. If there is no address scheme (that is, no http: prefix), then the value must begin with a slash and is treated relative to the root of the solution's repository.

The URL typically contains a specific revision or change number (as appropriate for the underlying SCM system) to freeze the external software at a specific, known state. Alternatively, if there is no revision or change number, the URL will track the latest changes on the specific trunk or branch.