Switch source_set stamp targets to phony targets

GN uses stamp files for a variety of output types as a mechanism for
completing a group of dependencies. Ninja's phony targets can be used in
the same manner. Semantically, stamp and phony only differ in one way:
if a phony target has no dependencies, then it is treated as always
dirty and is run every time.

The source_set output type always generates a stamp file in the target
ninja file. This CL replaces the source_set's stamp target with a phony
target. In the case where the source_set's new phony target does not
have any inputs, no targets will depend on it. An example of where that
might happen is a header only source_set. There are no object files to
generate, but targets that depend on the header only source_set will
generate dependencies on those headers through depfiles.

Bug: 187
Change-Id: I159f2f39a988eea189e4df9f5d9207fda6db5c58
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/9820
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
34 files changed
tree: dfeeb90a1d5b082d343511a45a26f63224a7334e
  1. build/
  2. docs/
  3. examples/
  4. infra/
  5. misc/
  6. src/
  7. tools/
  8. .clang-format
  9. .editorconfig
  10. .gitignore
  11. .style.yapf
  12. AUTHORS
  13. LICENSE
  14. OWNERS
  15. README.md
README.md

GN

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 https://gn.googlesource.com/gn
cd gn
python build/gen.py
ninja -C out
# To run tests:
out/gn_unittests

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.

Examples

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
./out/hello

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 https://gn-review.googlesource.com.

... 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’).

Community

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