Fix crash in "gn gen --ide=xcode" when project is malformed

As found while investigating, if the
project was malformed, "gn gen --ide=xcode" could crash due to
some undefined behaviour (likely dereferencing an uninitialised

This was due to FindApplicationTargetByName() using DCHECK to
enforce a property of the project when said property is not
under the control of the programmer but under the control of
the user writing the project's files.

Instead change the function implementation to return an error
if the expected property is not verified. That error is then
propagated back to the "gn gen" implementation and displayed
to the user.

All other uses of DCHECK/NOTREACHED in have
been inspected to verify they correspond to assertion about
the state of the code and do not depend on the properties of
the project's files.

Bug: 150
Change-Id: Ibe711f2d380ef0ed5dca637799563223c248ec7d
Commit-Queue: Brett Wilson <>
Reviewed-by: Brett Wilson <>
2 files changed
tree: ea62b6472be8f6e3699d6eb69b78838eb36d7049
  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.