|author||RJ Ascani <email@example.com>||Mon Oct 19 16:50:11 2020 -0700|
|committer||Commit Bot <firstname.lastname@example.org>||Fri Dec 11 17:17:17 2020 +0000|
Restat build.ninja after gen As of version 1.8, ninja caches mtimes in the .ninja_log file and will not restat a file if it has an entry in the .ninja_log. This becomes problematic for generator files such as build.ninja. In a scenario where the .ninja_log has an entry for build.ninja (ie, after ninja has had to trigger a re-gen) and a manual run of of `gn gen` has updated the build.ninja file, a subsequent invocation of ninja will trigger yet another re-gen of build.ninja. This can be reproduced like this: # Initial build gn gen out && ninja -C out # Trigger ninja re-gen so there's a build.ninja log entry touch BUILD.gn && ninja -C out # Manual re-gen gn gen out # The following command will re-gen again before building ninja -C out To work around this, the recommended approach from ninja is to use the ninja restat tool to get ninja to update the mtime in the .ninja_log. This CL does that by attempting to invoke `ninja -t restat build.ninja` immediately after the build.ninja is generated by `gn gen`. Because this tool was only introduced in 1.10, the usage is gated on having a ninja binary of at least that version. The ninja binary can be provided via the --ninja-executable switch. Bug: 136 Change-Id: If40391aa13e6ef71c4e8ab26aff57d66a8137b8e Reviewed-on: https://gn-review.googlesource.com/c/gn/+/10400 Commit-Queue: RJ Ascani <email@example.com> Reviewed-by: Brett Wilson <firstname.lastname@example.org>
GN is a meta-build system that generates build files for Ninja.
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
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
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:
If you find a bug, you can see if it is known or report it in the bug database.
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.
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You may ask questions and follow along with GN‘s development on Chromium’s gn-dev@ Google Group.