A Git submodule is a Git repository inside another Git repository. Chromium project doesn't rely on Git submodules directly. Instead, gclient sync is used to manage Git dependencies.
In 2023Q3, we started to move source of Git dependencies from DEPS files to Git submodules. While we do our best to hide complexities of submodules, some will be exposed.
Git submodules are managed via the combination of.gitmodules files and gitlinks..gitmodules is a text file that configures submodules, and each submodule entry contains the path to the submodule's worktree and the URL of the submodule. Gitlink is a special type of file in the Git database that tracks a submodule commit.
You can find an example of Git dependency below. Note that gclient-condition is a custom property used by gclient and not git. It's identical tocondition inDEPS and the allowed variables are defined invars = { section ofDEPS.
.gitmodules:
[submodule "third_party/catapult"]path = third_party/catapulturl = https://chromium.googlesource.com/catapult.gitgclient-condition = checkout_linux
gitlink entry, retrieved usinggit ls-files -s -- third_party/catapult:
160000 0b39a694c0b61392d1180520ed1c13e390029c41 0 third_party/catapult
Corresponding DEPS entry would look like:
'third_party/catapult': { 'url': 'https://chromium.googlesource.com/catapult.git@0b39a694c0b61392d1180520ed1c13e390029c41', 'condition': 'checkout_linux',}The simplest approach is to always run gclient sync after updating chromium checkout (e.g. aftergit pull, orgit checkout). You can automate that by adding post-checkout hook (example below). To confirm there are no changes, rungit status. If you usegit commit -a, check the “Changes to be committed” section that shows up in the edit commit message.
We need to have Git two hooks: post-checkout and post-merge. In chromium/src directory, edit.git/hooks/post-checkout:
#!/bin/shset -ugclient sync
and set it to be executable:chmod +x .git/hooks/post-checkout. Repeat the same for.git/hooks/post-merge.
More information about githooks can be foundhere.
If a submodule is checked out at a different commit than one tracked by its parent,git status in the parent repo will show unstaged changes with “new commits” in parenthesis, such as:
modified: <git deps name> (new commits)
Commands likegit commit -a orgit add *|.|-A|u WILL include this in your commit and your CL (which is likely NOT what you want).
Instead you can:
# Run gclient sync to sync dependenciesgclient sync# check git status again# ORgit add <file> # for each file you want to stage# Then commit your staged filesgit commit -v -m "Fix foo/bar"
If a submodule has uncommitted changes (i.e. you made some manual changes to the affected submodule), runninggit status in its parent repo will show them as unstaged changes:
modified: <git deps name> (modified content)# or modified: <git deps name> (untracked content)
It's not possible to add those changes to the parent repository. You can ignore such status, or you can cd into submodule and address it. E.g. you may delete untracked files (content) or reset modified content to match HEAD.
If you accidentally stage a Git submodule, you can unstage it by runninggit restore --staged <path to submodule>.
We will need to create either a commit that sets it back to old value, or amend the commit that added it. You can try to rungclient sync to bring the commit back to what is expected. If that doesn't work, you can usegclient setdep -r <path>@<old hash>, rungclient gitmodules to sync all submodules commits back to what is in DEPS, or check detailed instructions inManaging dependencies.
NOTE: setdep for chromium/src is always prefixed with src/. For example, if you are updating v8, the command would be `gclient setdep -r src/v8@.
Forgit status, submodules that show up underChanges not staged for commit can be hidden withgit -c diff.ignoreSubmodules=all status
Forgit commit -a you can exclude all submodules withgit -c diff.ignoreSubmodules=all commit -a.
git add does NOT supportdiff.ignoreSubmodules. Submodules that were hidden from you withgit -c diff.ignoreSubmodules=all status would still be staged withgit add .|--all|-A and therefore committed withgit -c diff.ignoreSubmodules=all commit.
Instead you can rungit add ':(exclude,attr:builtin_objectmode=160000)' which will stage all changes except for submodules.
(git assigns160000 as the objectmode submodules. You can read more aboutbuiltin_objectmode and magicpathspecs)
To make these commands shorter, you can create git aliases for them by adding the following to your $HOME/.gitconfig (globally) or src/.git/config file (just chromium/src):
[alias] # 's', 'c', or whatever alias you want for each command s = -c diff.ignoreSubmodules=all status c = -c diff.ignoreSubmodules=all commit -a d = -c diff.ignoreSubmodules=all difftool --dir-diff a = add ':(exclude,attr:builtin_objectmode=160000)'
With the above, you can execute these commands by runninggit s,git c, etc. Or you may also use the pre-commit git hook detailed below.
git config diff.ignoreSubmodules sets a default behavior fordiff,status, and several other git subcommands, using one of thesupported values of--ignore-submodules.
By default,gclient sync sets this todirty as a local config in the chromium checkout. This elides submodule output forgit status in a clean checkout, but will show submodules as modified when developers locally touch them.
Manually setting this toall elides such output in all cases. This also omits submodule changes fromgit commit -a, which can decrease the likelihood of accidental submodule commits. However, it does not omit such changes fromgit add -A, meaning developers who use this flow are actuallymore likely to commit accidental changes, since they'll be invisible beforehand unless developers manually set--ignore-submodules=dirty or use a lower-level command such asgit diff-tree.
Becauseall can result in misleading output and doesn't fully prevent accidental submodule commits, typical developers are likely better-served by leaving this configured todirty and installing thecommit hook described below to prevent such commits. Accordingly,gclient sync will warn if it detects a different setting locally; developers who understand the consequences can silence the warning via theGCLIENT_SUPPRESS_SUBMODULE_WARNING environment variable.
While resolving merge conflicts during agit rebase-update you may see submodules show up in unexpected places.
Submodules under this section can be safely ignored. This simply shows that the local commits of these submodules do not match the latest pinned commits fetched from remote. In other words, these submodules have been rolled since your lastgit rebase-update.
If you use a diff tool like meld you can run:git -c diff.ignoreSubmodules=all difftool --dir-diff to prevent these submodules from showing up in your diff tool.
If Submodules show up under this section it means that new revisions were committed for those submodules (either intentional or unintentionally) and these submodules were also rolled at remote. So now there is a conflict.
If you DID NOT intentionally make any submdoules changes, you should run:gclient gitmodules. This will update the submdoules for you, to match whatever commits are listed in DEPS (which you have just pulled from remote).
If you DID intentionally roll submodules, you can resolve this conflict just by resetting it:gclient setdep -r {path}@{hash}
depot_tools provides an opt-in pre-commit hook to detect unintentional submodule changes duringgit commit and remove them from the commit.
To install the hook:gclient installhooks
If there is an existing pre-commit hook, gclient will instruct you how to update it. If you have already installed this hook, gclient will do nothing.
To uninstall the hook, inchromium/srcrm .git/hooks/pre-commit if you have no other hooks. Otherwise update.git/hooks/pre-commit to remove the gclient provided hook.
To bypass this hook rungit commit --no-verify (which bypasses all hooks you may have) OR set the following environment variable:SKIP_GITLINK_PRECOMMIT=1 (which bypasses this specific hook).
Note that this is currently and best effort solution and does not guarantee that unintentional commits will always be detected. The team will iterate quickly on this hook to fill in other gaps and behavior is subject to change. Please file anissue for any feedback.
Lots of Chromium infrastructure already parse DEPS file directly. Instead of a massive switch, it's easier to transition to Git submodules this way. Moreover, unwanted Git submodule updates can be detected and developers can be warned.
See thedependencies page.
First, you will need to determine what is the right commit hash. If you accidentally committed a gitlink, which got in the meantime updated, you most likely want to restore the original updated gitlink. You can rungclient gitmodules, which will take care of all unmerged submodule paths, and set it to match DEPS file.
If you prefer to manually resolve it, under git status, you will see “Unmerged paths”. If those are submodules, you want to restore them by running the following command:
git restore --staging <affected path>
gclient getdep will return whatever commit is pinned for the deps inDEPS (unstaged, staged, or committed). If the repo is using git submodules only (and has no git deps inDEPS) it will return the whatever pinned commit is staged or committed.
gclient getdep -r <path>
If you want to keep your gitlink, then rungit add <affected path>.
Please filea bug under Infra>SDK component.