clang: Fixes to module support

1. -fmodules-embed-all-files is a cc1 flag, and should have been passed
   to clang++ via -Xclang.

2. Don't require a .cc in the target to emit the module_deps variables
   (this is to be able to compile a target that contains only a
   .modulemap, e.g. the C++ std module).

3. Add {{module_deps_no_self}}, which is the same as {{module_deps}}
   except that it excludes the flags to include the pcm for the current

   That is, for A depending on B, and both using modules, when building
   for A, {{module_deps}} will reference both A.pcm and B.pcm, and so
   can be used to build .cc files in A. By contrast,
   {{module_deps_no_self}} for A will only reference B.pcm, and so can
   be used to build A.pcm.

Bug: fuchsia:27276
Change-Id: I239d1c5cd4d5d167251801b1347b02e8d89caeee
Reviewed-by: Brett Wilson <>
Commit-Queue: Scott Graham <>
7 files changed
tree: 799f65f50f3c8d3bcc0570641e2fbdd821f5f0e4
  1. build/
  2. docs/
  3. examples/
  4. infra/
  5. misc/
  6. src/
  7. tools/
  8. .clang-format
  9. .editorconfig
  10. .gitignore
  11. .style.yapf
  14. 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.