doc/BranchingAndRolling.md - platform/external/angle - Git at Google

 # How to Branch and Roll Chromium's ANGLE Dependency

 ANGLE provides an implementation of OpenGL ES on top of other APIs (e.g. DirectX11, Vulkan). ANGLE
 uses (i.e. depends upon) other third-party software that comes from different repositories. ANGLE specifies
 its dependencies on a specific version of each of these other repositories in the [ANGLE DEPS file](https://chromium.googlesource.com/angle/angle/+/main/DEPS).

 Chromium relies upon ANGLE for hardware accelerated rendering and WebGL support. Chromium similarly
 specifies its dependency on a specific version of ANGLE in the [Chromium repository's src/DEPS file](http://src.chromium.org/viewvc/chrome/trunk/src/DEPS).

 This document describes how to update those dependencies, and, if necessary, create an ANGLE branch
 to correspond to a branched release of Chrome.

 ANGLE's commit queue also runs browser-level tests which are hosted in
 the Chromium repository. To reduce the chance of a Chromium-side
 change breaking ANGLE's CQ, the version of Chromium against which
 ANGLE changes is also snapshotted, and rolled forward into ANGLE with
 appropriate testing.

 ## Autorollers

 At present, autorollers manage both the ANGLE roll into Chromium, and
 the Chromium roll into ANGLE. There is also an autoroller for ANGLE into [Android AOSP](https://android.googlesource.com/platform/external/angle/).
 All of the ANGLE-related autorollers are documented in the [ANGLE Wrangling documentation](../infra/ANGLEWrangling.md#the-auto-rollers).

 ## Manually rolling DEPS

 As mentioned above, dependencies are encoded in `DEPS` files. The process to update a given
 dependency is as follows:

  * Find the appropriate line in the relevant `DEPS` file that defines the dependency
  * Change the [git SHA-1 revision number](http://git-scm.com/book/ch6-1.html) to be that of the commit
 on which to depend upon (Note: use the full SHA-1, not a
 shortened version)
  * You can find the SHA-1 for a particular commit with `git log` on the appropriate branch of the
 repository, or via a public repository viewer
  * If using the [ANGLE public repository viewer](https://chromium.googlesource.com/angle/angle), you will need to select the branch whose log you
 wish to view from the list on the left-hand side, and then click on the "tree" link at the top of
 the resulting page. Alternatively, you can navigate to
 `https://chromium.googlesource.com/angle/angle/+/<branch name>/` --
 including the terminating forward slash. (e.g.
 `https://chromium.googlesource.com/angle/angle/+/main/`)

 ### Rolling Vulkan Memory Allocator (VMA)

 ANGLE and other Google projects (e.g. Skia, Chrome) use the open-source [Vulkan Memory Allocator][vma-upstream] (VMA)
 library. As with with other external repositories, these projects do not directly use the [upstream Vulkan Memory Allocator][vma-upstream] repository.
 Instead, a [Google-local repository][vma-chrome] is used, which contains Google-local changes and fixes (e.g. changes
 to `BUILD.gn`). This Google-local repository repository contains the following key branches:

 - `upstream/master` is automatically mirrored with the contents of the [upstream VMA][vma-upstream] repository
 - `main` is manually curated by Google, with a combination of upstream and Google-local changes

 ANGLE's `DEPS` file points to a git SHA-1 revision of the `main` branch.

 Manual rolls of the `main` branch currently involve rebasing all of the Google-local changes on top of newer upstream changes. The current process (done in 2022) is to:

  * Revert all of the Google-local changes (i.e. with a single commit)
  * Merge or cherry-pick all of the upstream changes
  * Cherry-pick the Google-local changes on top
  * Note: it may be possible to simply merge future upstream changes directly, without reverting the Google-local changes

 Manual rolls of which SHA-1 revision the ANGLE's `DEPS` file points to is done via the process
 outlined above. Within an ANGLE build, you can navigate to the `third_party/vulkan_memory_allocator`
 directory, check out the `main` branch, and use `git log` to select the desired Git revision.
 **Please note** that cross-project coordination may be required when rolling VMA, as some projects (e.g. Chrome) builds itself with a single VMA version across Chrome, ANGLE, and Skia.

 [vma-upstream]: https://github.com/GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator
 [vma-chrome]: https://chromium.googlesource.com/external/github.com/GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator

 Note: When ANGLE is AutoRolled to the Android AOSP source tree, Google-local
 changes to the VMA `BUILD.gn` file will be converted to the ANGLE `Android.bp` file.

 ## Branching ANGLE

 Sometimes, individual changes to ANGLE are needed for a release of Chrome which
 has already been branched. If this is the case, a branch of ANGLE should be
 created to correspond to the Chrome release version, so that Chrome may
 incorporate only these changes, and not everything that has been committed since
 the version on which Chrome depended at branch time. **Please note: Only ANGLE
 admins can create a new branch.** To create a branch of ANGLE for a branched
 Chrome release:

  * Determine what the ANGLE dependency is for the Chrome release
 by checking the DEPS file for that branch.
  * Check out this commit as a new branch in your local repository.
    * e.g., for [the Chrome 34 release at
 chrome/branches/1847](http://src.chromium.org/viewvc/chrome/branches/1847/src/DEPS),
 the ANGLE version is 4df02c1ed5e97dd54576b06964b1da67ea30238e. To
 check this commit out locally and create a new branch named 'mybranch'
 from this commit, use: ```git checkout -b mybranch
 4df02c1ed5e97dd54576b06964b1da67ea30238e```
  * To create this new branch in the public repository, you'll need to push the
 branch to the special Gerrit reference location, 'refs/heads/<branch name>'. You
 must be an ANGLE administrator to be able to push this new branch.
     * e.g., to use your local 'mybranch' to create a branch in the public repository called
 'chrome\_m34', use: ```git push origin mybranch:refs/heads/chrome_m34```
     * The naming convention that ANGLE uses for its release-dedicated branches is 'chrome\_m##'.
	# How to Branch and Roll Chromium's ANGLE Dependency

	ANGLE provides an implementation of OpenGL ES on top of other APIs (e.g. DirectX11, Vulkan). ANGLE
	uses (i.e. depends upon) other third-party software that comes from different repositories. ANGLE specifies
	its dependencies on a specific version of each of these other repositories in the [ANGLE DEPS file](https://chromium.googlesource.com/angle/angle/+/main/DEPS).

	Chromium relies upon ANGLE for hardware accelerated rendering and WebGL support. Chromium similarly
	specifies its dependency on a specific version of ANGLE in the [Chromium repository's src/DEPS file](http://src.chromium.org/viewvc/chrome/trunk/src/DEPS).

	This document describes how to update those dependencies, and, if necessary, create an ANGLE branch
	to correspond to a branched release of Chrome.

	ANGLE's commit queue also runs browser-level tests which are hosted in
	the Chromium repository. To reduce the chance of a Chromium-side
	change breaking ANGLE's CQ, the version of Chromium against which
	ANGLE changes is also snapshotted, and rolled forward into ANGLE with
	appropriate testing.

	## Autorollers

	At present, autorollers manage both the ANGLE roll into Chromium, and
	the Chromium roll into ANGLE. There is also an autoroller for ANGLE into [Android AOSP](https://android.googlesource.com/platform/external/angle/).
	All of the ANGLE-related autorollers are documented in the [ANGLE Wrangling documentation](../infra/ANGLEWrangling.md#the-auto-rollers).

	## Manually rolling DEPS

	As mentioned above, dependencies are encoded in `DEPS` files. The process to update a given
	dependency is as follows:

	* Find the appropriate line in the relevant `DEPS` file that defines the dependency
	* Change the [git SHA-1 revision number](http://git-scm.com/book/ch6-1.html) to be that of the commit
	on which to depend upon (Note: use the full SHA-1, not a
	shortened version)
	* You can find the SHA-1 for a particular commit with `git log` on the appropriate branch of the
	repository, or via a public repository viewer
	* If using the [ANGLE public repository viewer](https://chromium.googlesource.com/angle/angle), you will need to select the branch whose log you
	wish to view from the list on the left-hand side, and then click on the "tree" link at the top of
	the resulting page. Alternatively, you can navigate to
	`https://chromium.googlesource.com/angle/angle/+/<branch name>/` --
	including the terminating forward slash. (e.g.
	`https://chromium.googlesource.com/angle/angle/+/main/`)

	### Rolling Vulkan Memory Allocator (VMA)

	ANGLE and other Google projects (e.g. Skia, Chrome) use the open-source [Vulkan Memory Allocator][vma-upstream] (VMA)
	library. As with with other external repositories, these projects do not directly use the [upstream Vulkan Memory Allocator][vma-upstream] repository.
	Instead, a [Google-local repository][vma-chrome] is used, which contains Google-local changes and fixes (e.g. changes
	to `BUILD.gn`). This Google-local repository repository contains the following key branches:

	- `upstream/master` is automatically mirrored with the contents of the [upstream VMA][vma-upstream] repository
	- `main` is manually curated by Google, with a combination of upstream and Google-local changes

	ANGLE's `DEPS` file points to a git SHA-1 revision of the `main` branch.

	Manual rolls of the `main` branch currently involve rebasing all of the Google-local changes on top of newer upstream changes. The current process (done in 2022) is to:

	* Revert all of the Google-local changes (i.e. with a single commit)
	* Merge or cherry-pick all of the upstream changes
	* Cherry-pick the Google-local changes on top
	* Note: it may be possible to simply merge future upstream changes directly, without reverting the Google-local changes

	Manual rolls of which SHA-1 revision the ANGLE's `DEPS` file points to is done via the process
	outlined above. Within an ANGLE build, you can navigate to the `third_party/vulkan_memory_allocator`
	directory, check out the `main` branch, and use `git log` to select the desired Git revision.
	Please note that cross-project coordination may be required when rolling VMA, as some projects (e.g. Chrome) builds itself with a single VMA version across Chrome, ANGLE, and Skia.

	[vma-upstream]: https://github.com/GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator
	[vma-chrome]: https://chromium.googlesource.com/external/github.com/GPUOpen-LibrariesAndSDKs/VulkanMemoryAllocator

	Note: When ANGLE is AutoRolled to the Android AOSP source tree, Google-local
	changes to the VMA `BUILD.gn` file will be converted to the ANGLE `Android.bp` file.

	## Branching ANGLE

	Sometimes, individual changes to ANGLE are needed for a release of Chrome which
	has already been branched. If this is the case, a branch of ANGLE should be
	created to correspond to the Chrome release version, so that Chrome may
	incorporate only these changes, and not everything that has been committed since
	the version on which Chrome depended at branch time. **Please note: Only ANGLE
	admins can create a new branch.** To create a branch of ANGLE for a branched
	Chrome release:

	* Determine what the ANGLE dependency is for the Chrome release
	by checking the DEPS file for that branch.
	* Check out this commit as a new branch in your local repository.
	* e.g., for [the Chrome 34 release at
	chrome/branches/1847](http://src.chromium.org/viewvc/chrome/branches/1847/src/DEPS),
	the ANGLE version is 4df02c1ed5e97dd54576b06964b1da67ea30238e. To
	check this commit out locally and create a new branch named 'mybranch'
	from this commit, use: ```git checkout -b mybranch
	4df02c1ed5e97dd54576b06964b1da67ea30238e```
	* To create this new branch in the public repository, you'll need to push the
	branch to the special Gerrit reference location, 'refs/heads/<branch name>'. You
	must be an ANGLE administrator to be able to push this new branch.
	* e.g., to use your local 'mybranch' to create a branch in the public repository called
	'chrome\_m34', use: ```git push origin mybranch:refs/heads/chrome_m34```
	* The naming convention that ANGLE uses for its release-dedicated branches is 'chrome\_m##'.