More efficient Value implementation.

Using a union to store all possible inner data-types means less
work whenever creating / copying / moving / destroying values,
and small size for each instance.

This results in a slightly faster "gn gen" operation, using
slightly less memory, i.e. when used with a Chromium checkout:

  $ /usr/bin/time -f "%M %U" /tmp/aa/gn-origin gen out/Release
  Done. Made 21651 targets from 1614 files in 6339ms
  764468 25.30

  $ /usr/bin/time -f "%M %U" /tmp/aa/gn-better-value gen out/Release
  Done. Made 21651 targets from 1614 files in 6014ms
  738132 23.27

R=brettw@chromium.org,dpranke@chromium.org
BUG=NONE

Change-Id: I6804857b1e69653713f038903f9abbbcae6ec62c
Reviewed-on: https://gn-review.googlesource.com/c/3662
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
2 files changed
tree: b03ac2bc9433237324b910cfdec1bfc293767663
  1. .clang-format
  2. .editorconfig
  3. .gitignore
  4. .style.yapf
  5. AUTHORS
  6. LICENSE
  7. OWNERS
  8. README.md
  9. base/
  10. build/
  11. docs/
  12. infra/
  13. tools/
  14. util/
README.md

GN

GN is a meta-build system that generates build files for Ninja. There is documentation in docs/ and a presentation on it.

Getting started

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.

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 cl upload --gerrit

When revising a change, use:

git commit --amend
git cl upload --gerrit

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 w/ GN‘s development on Chromium’s gn-dev@ Google Group.