Match all toolchains by default.

GN was originally designed expecting that most users would only want to
interact with the default toolchain. As a result, most introspection
commands match only targets in the default toolchain by default.

But some builds have made greater use of the toolchain feature. For
example, in Fuchsia, allshared libraries and all of their dependencies
are compiled in a special "shared" toolchain with "position independent
code" enabled. Most users are not aware of this. So in such builds,
having introspection commands only match targets in the default
toolchain can be surprising and look broken.

This changes the default to match all toolchains for introspection
commands that can take labels. A new --default-toolchain flag is added
for the default behavior, and the previous --all-toolchains flag is

Change-Id: Ifa0dfa5b8c792c115443776f3b992d2d6b03bf02
Reviewed-by: Scott Graham <>
Commit-Queue: Brett Wilson <>
9 files changed
tree: a333c04332e1da5a192f306d619add941dec568f
  1. build/
  2. docs/
  3. examples/
  4. infra/
  5. misc/
  6. src/
  7. .clang-format
  8. .editorconfig
  9. .gitignore
  10. .style.yapf
  13. OWNERS


GN is a meta-build system that generates build files for Ninja.

Related resources:

Getting a binary

You can download the latest version of GN binary for Linux, macOS and Windows.

Alternatively, you can build GN from source:

git clone
cd gn
python build/
ninja -C out
# To run tests:

On Windows, it is expected that cl.exe, link.exe, and lib.exe can be found in PATH, so you'll want to run from a Visual Studio command prompt, or similar.

On Linux and Mac, the default compiler is clang++, a recent version is expected to be found in PATH. This can be overridden by setting CC, CXX, and AR.


There is a simple example in examples/simple_build directory that is a good place to get started with the minimal configuration.

To build and run the simple example with the default gcc compiler:

cd examples/simple_build
../../out/gn gen -C out
ninja -C out

For a maximal configuration see the Chromium setup:

and the Fuchsia setup:

Reporting bugs

If you find a bug, you can see if it is known or report it in the bug database.

Sending patches

GN uses Gerrit for code review. The short version of how to patch is:

Register at

... edit code ...
ninja -C out && out/gn_unittests

Then, to upload a change for review:

git commit
git push origin HEAD:refs/for/master

The first time you do this you'll get an error from the server about a missing change-ID. Follow the directions in the error message to install the change-ID hook and run git commit --amend to apply the hook to the current commit.

When revising a change, use:

git commit --amend
git push origin HEAD:refs/for/master

which will add the new changes to the existing code review, rather than creating a new one.

We ask that all contributors sign Google's Contributor License Agreement (either individual or corporate as appropriate, select ‘any other Google project’).


You may ask questions and follow along with GN‘s development on Chromium’s gn-dev@ Google Group.