Braid is a simple tool to help track vendor branches in a Git repository.
Vendoring allows you take the source code of an external library and ensure it's version controlled along with the main project. This is in contrast to including a reference to a packaged version of an external library that is available in a binary artifact repository such as Maven Central, RubyGems or NPM.
Vendoring is useful when you need to patch or customize the external libraries or the external library is expected to co-evolve with the main project. The developer can make changes to the main project and patch the library in a single commit.
The problem arises when the external library makes changes that you want to integrate into your local vendored version or the developer makes changes to the local version that they want integrated into the external library.
A typical "implementation" of vendoring is to simply download or checkout the
source for the external library, remove the
.svn directories and
commit it to the main source tree. However this approach makes it very difficult
to update the library. When you want to update the library do you re-apply your
local changes onto a new copy of the vendored library or do you re-apply the
changes from the external library to local version? Both cases involve manual
generation and application of patch files to source trees.
This is where Braid comes into play. Braid makes it easy to vendor in remote git repositories and use an automated mechanism for updating the external library and generating patches to upgrade the external library.
Braid creates a file
.braids.json in the root of your repository that contains
references to external libraries or mirrors. The configuration allows you to control
aspects of the mirroring process such as;
- whether the mirror is locked to a particular version of the external library.
- whether the mirror is tracking a tag or a branch.
- whether the mirror includes the entire external library or just a subdirectory.
gem install braid
Quick usage - ruby project
Let's assume we're writing the project
myproject that needs grit in lib/grit. Initialize the repo (nothing braid related here):
git init myproject cd myproject touch README git add README git commit -m "initial commit"
Now let's vendor grit:
braid add git://github.com/mojombo/grit.git lib/grit
And you're done! Braid vendored grit into lib/grit. Feel free to inspect the changes with git log or git show.
If further down the line, you want to bring new changes from grit into your repository, just update the mirror:
braid update lib/grit
If you make changes to the grit library and want to generate a patch file so that you can submit the patch file to the grit project:
braid diff lib/grit > grit.patch
Alternatively you can push changes back to the source directory directly using the following command. The command
will push the changes to the branch
myproject_customizations that has been branched off the source branch (
in this example). Omit the
--branch argument to push directly to the source branch.
braid push lib/grit --branch myproject_customizations
Once those changes have been applied to grit you probably want to update your local version of grit again.
braid update lib/grit
Use the built in help system to find out about all commands and options:
braid help braid help add # or braid add --help
Adding a mirror
braid add git://github.com/rails/rails.git vendor/rails
Adding a subdirectory from a mirror
This is useful if you want to add a subdirectory from a mirror into your own project.
braid add --path dist https://github.com/twbs/bootstrap.git vendor/assets/bootstrap
Adding a mirror based on a branch
braid add --branch 5-0-stable https://github.com/rails/rails.git vendor/rails
Adding a mirror based on a tag
braid add --tag v1.0 https://github.com/realityforge/backpack.git vendor/tools/backpack
Adding mirror locked to a revision
braid add --revision bf1b1e0 git://github.com/rails/rails.git vendor/rails
# Update a specific mirror braid update vendor/plugins/cache_fu # Update all mirrors braid update
Updating mirrors with conflicts
If a braid update creates a conflict, braid will stop execution and leave the partially committed files in your working copy, just like a normal git merge conflict would.
You will then have to resolve all conflicts and manually run
git commit. The commit message is
If you want to cancel the braid update and the merge, you'll have to reset your working copy and
git reset --hard.
Locking and unlocking mirrors
Lock to a particular version in the mirror.
braid update --revision 6c1c16b vendor/rails
Go back to tracking a particular branch.
braid update --branch master vendor/rails
Showing local changes made to mirrors
braid diff vendor/rails
Braid version compatibility
Since Braid has been regularly changing the configuration format and adding new features that some projects may choose to rely on, and somewhat less often making breaking changes in how the configuration is handled, problems can arise if different developers work on the same project using different versions of Braid. Since version 1.1.0, Braid refuses to operate if it detects potentially problematic version skew. If this happens, Braid will tell you what you can do. If you'd like an overview of what to expect, read on.
Roughly speaking, the
.braids.json configuration file contains a configuration
version number that corresponds to a range of compatible Braid minor versions
x.y). "Patch" upgrades to Braid (i.e.,
x.y.(z+1)) will never
(intentionally!) have configuration compatibility implications and are always
recommended as they may fix critical bugs.
If you use a Braid version too old for your configuration file, Braid will direct you to the configuration version history page with instructions to upgrade Braid. If you use a Braid version too new, Braid will tell you how you can upgrade your configuration file or find a compatible older Braid version to use. (As an exception, a newer version of Braid can run read-only commands on an older configuration file without upgrading it if there are no breaking changes.) If you upgrade your configuration file, then other developers on the project may need to upgrade Braid. Braid does not support downgrading a configuration file, though you can revert the commit that upgraded it if you haven't made any subsequent changes to the configuration.
If you work on multiple projects, you may need to install multiple versions of Braid and manually run the correct version for each project. Fortunately, the RubyGems system makes this reasonably straightforward.
Another approach is to standardize the Braid version for a project by listing
Braid in a
Gemfile (either checking in
Gemfile.lock or using a version
constraint in the
Gemfile) and run the project's version of Braid via
bundle exec braid. Even non-Ruby projects
can do this if it's acceptable to have a
projects that don't want Braid to interact with their other gems can potentially
Gemfile in a subdirectory and provide a wrapper script for
that sets the
BUNDLE_GEMFILE environment variable. We do not yet have enough
experience with this approach to make a firm recommendation for or against it.
This is the best design we could find to prevent surprises and adequately support normal development processes while minimizing the additional maintenance cost of the version compatibility mechanism. We want to have a scheme in place that is robust enough to make it reasonable to encourage serious adoption of Braid, yet we don't want to spend extra work adding conveniences until there's evidence of sufficient demand for them.
We appreciate any patches, error reports and usage ideas you may have. Please submit an issue or pull request on GitHub.
While preparing to release Braid v1.0 the support for subversion repositories was removed as there was no active maintainers and inadequate test coverage. If there is anyone motivated to re-add and maintain the Subversion support, please contact the authors.
- Cristi Balan
- Norbert Crombach
- Peter Donald
- Alan Harper
- Brad Durrow
- Christoph Sturm
- Dennis Muhlestein
- Ferdinand Svehla
- Matt McCutchen
- Michael Klishin
- Roman Heinrich
- Travis Tilley
- Tyler Rick