Re: [chromium-dev] chromium-packagers: Switch Ninja to Siso

[Avi Drissman]

+Chromium Embedders in case there are any folks on that list who didn't get this notification.

On Wed, Jun 18, 2025 at 9:33 PM 'Junji Watanabe' via Chromium-dev <chromi...@chromium.org> wrote:

(bcc chromium-dev@)

Let me fork the thread since I got responses from different people.

Chromium for Linux distros:

How do they build Chromium now? They are supposed to use the GN/Ninja binaries fetched via DEPS.

Siso also should be fetched via DEPS, as well.

Electron:

I got a message from Electron, and am discussing it with them.

CEF:

Looking at the repo, there are GN config files, Bazel files, CMake files. So, it's not clear how they build the Chromium part. 

Does anyone know who I should notify the PSA?

Node:

I'm also not familiar with how the official Node releases are built. Although there are GN configs, they don't seem to be used for Node official builds. 

I guess they still use GYP presumably with Make? Note that V8 has migrated to Siso already.

Thank you,

Junji

On Tue, Jun 17, 2025 at 6:53 PM Raphael Kubo da Costa <ku...@igalia.com> wrote:

+chromium-packagers

Hey Junji,

Given the "Ninja builds may eventually stop working" bit, can you clarify how this impacts downstreams like Linux distros that build Chromium from the published tarballs, or embedders like Electron, CEF, perhaps even Node due to V8?

Specifically, I'm wondering:

* Will there be releases like Ninja does?

* If not, I'm guessing everyone will be expected to fetch and build their own Siso copy?

* Are Siso versions supposed to be pinned to specific Chromium releases like GN?

On 6/17/25 11:17, 'Junji Watanabe' via Chromium-dev wrote:

Hi Dirk,

Thank you for your questions. Let me clarify.

Regarding your first question, there are a few reasons for moving away from Ninja:

Maintenance Cost: Currently, we have limited testing for Ninja and Reclient builds on our CI builders. While we are still addressing and fixing any issues that arise, our goal is to discontinue support for Ninja after the upcoming deadline.

Build Improvements: We're planning to improve our build processes by integrating GN and Siso more closely. This includes features like mtime-less builds and more efficient build graph serialization. It's difficult to predict how challenging it will be to maintain compatibility with Ninja as we implement these improvements, and it's possible that Ninja builds may eventually stop working. So, we encourage switching to Ninja soon. If you encounter any workflow issues with Siso, please provide feedback. 

Regarding your question about Siso's support for other RBE backends, Siso is designed to send Remote Execution API (REAPI) requests to a custom API address. I am currently in contact with various remote build service providers to confirm full compatibility with Siso's REAPI support.

Thank you,

Junji

On Tue, Jun 17, 2025 at 12:36 AM Dirk Pranke <dpr...@chromium.org> wrote:

Hi Junji,

Presumably GN is still generating .ninja files that work with Ninja, so what are the implications of this for people that aren't using remote execution to build? Are we going to be making changes that aren't compatible with Ninja? 

Or is this more of a support thing, in that you only want to support one build tool?

Also, does Siso support building with other RBE backends?

-- Dirk

On Mon, Jun 16, 2025 at 2:00 AM 'Junji Watanabe' via build <bu...@chromium.org> wrote:

Hi everyone,

This PSA is for all external Chromium developers regarding an upcoming change to the Chromium build system.

What's changing?

Chromium's build system is switching from Ninja 🥷 to Siso 🌿. This migration has already been completed for developers and CI/CQ within Google, and we are now extending it to our external contributors.

Siso is developed by the Chrome Build Infra Team at Google as a drop-in replacement for Ninja to support remote execution natively.

What do you need to do?

Just keep building Chromium with autoninja. autoninja will automatically use Siso after you run gn clean the next time.

How to opt out? 

If you encounter problems with Siso, you can switch back by setting use_siso=false in your args.gn.

About Ninja/Reclient/GN

• GN will stay the same as before.

• Reclient will be removed from Chromium at the end of September.

• Ninja will be unsupported after the end of September.

Please prepare to switch to Siso before the deadline.

Questions or Issues?

If you have any questions or run into any problems with this change, please don't hesitate to reach out to us:

• Slack: #build

• Chromium Issue Tracker: File a Siso bug.

• Email: bu...@chromium.org

Thanks,

Junji - on behalf of the Chrome Build Infra Team

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