Build a Simple Project using GN: A Step-by-Step Guide

Welcome to this comprehensive guide on building a simple project using GN (Generate Ninja), a meta-build system that allows you to define your build process in a more concise and explicit way. In this article, we’ll walk you through the entire process, from setting up your environment to building and running your project. So, buckle up and let’s get started!

What is GN?

GN (Generate Ninja) is a meta-build system developed by the Chromium team. It’s designed to be fast, scalable, and flexible, making it an ideal choice for large and complex projects. GN allows you to define your build process in a Python-like syntax, which makes it easy to understand and maintain. GN generates Ninja build files, which can be used to build your project.

Setting up your Environment

Before we dive into the project, let’s make sure our environment is set up correctly. You’ll need to install the following:

• GN (Generate Ninja)
• Ninja (build system)
• A C/C++ compiler (e.g., GCC or Clang)
• An editor or IDE of your choice

Once you have installed GN and Ninja, you’re ready to move on to the next step.

Creating a New Project

Let’s create a new project directory and navigate to it:

mkdir myproject
cd myproject

Now, let’s create a new file called BUILD.gn, which will contain our build configuration:

gn init

This will create a basic BUILD.gn file with some default settings.

Defining our Project

In this example, we’ll create a simple C++ project that prints “Hello, World!” to the console. Let’s modify our BUILD.gn file to include the following:

executable("hello_world") {
  sources = [ "hello_world.cc" ]
  deps = []
}

This defines an executable target called hello_world, which depends on a single source file hello_world.cc.

Writing our Source Code

Now, let’s create our source file hello_world.cc:

#include 

int main() {
  std::cout << "Hello, World!" << std::endl;
  return 0;
}

This is a simple C++ program that prints "Hello, World!" to the console.

Building our Project

Now that we have our build configuration and source code in place, let's build our project:

gn gen out
ninja -C out

The first command generates the Ninja build files, and the second command builds our project using Ninja.

Running our Project

Finally, let's run our project:

./out/hello_world

This should print "Hello, World!" to the console.

GN Syntax

Now that we've completed our simple project, let's take a closer look at the GN syntax.

Targets

In GN, a target represents a buildable entity, such as an executable, library, or source file. Targets are defined using the executable(), library(), or source_set() functions.

executable("hello_world") {
  ...
}

library("mylib") {
  ...
}

source_set("mysources") {
  ...
}

Dependencies

Dependencies are used to specify the relationships between targets. In our example, we defined an executable target that depends on a single source file:

executable("hello_world") {
  sources = [ "hello_world.cc" ]
  deps = []
}

We can also specify dependencies between targets:

executable("hello_world") {
  deps = [ ":mylib" ]
}

library("mylib") {
  sources = [ "mylib.cc" ]
}

Configurations

Configurations are used to specify build settings, such as compiler flags and include directories. We can define a configuration and apply it to our target:

config("myconfig") {
  defines = [ "MY_DEFINE" ]
  include_dirs = [ "include" ]
}

executable("hello_world") {
  configs = [ ":myconfig" ]
  sources = [ "hello_world.cc" ]
  deps = []
}

GN Modules

GN modules are reusable pieces of build logic that can be imported and used in multiple projects. Let's create a simple GN module called my_module.gn:

module("my_module") {
  deps = [ "//third_party/mylib" ]
  includes = [ "my_header.h" ]
}

We can then import this module in our BUILD.gn file:

import("//my_module.gn")

executable("hello_world") {
  sources = [ "hello_world.cc" ]
  deps = [ ":my_module" ]
}

Conclusion

In this article, we've covered the basics of building a simple project using GN. We've defined our project, written our source code, and built and run our project using GN and Ninja. We've also explored the GN syntax, including targets, dependencies, configurations, and modules.

GN provides a flexible and scalable way to define your build process, making it an ideal choice for large and complex projects. With this guide, you're ready to start building your own projects using GN.

Additional Resources

For more information on GN, check out the following resources:

• GN documentation
• GN FAQ
• Ninja documentation

Frequently Asked Questions

Here are some frequently asked questions about GN:

Q	A
What is GN?	GN is a meta-build system that generates Ninja build files.
What is Ninja?	Ninja is a build system that uses build files generated by GN.
How do I define a target in GN?	You can define a target using the executable(), library(), or source_set() functions.
How do I specify dependencies in GN?	You can specify dependencies using the deps variable in your target definition.

I hope this guide has provided a comprehensive introduction to building a simple project using GN. Happy building!

Frequently Asked Question

If you're new to using GN, you probably have a lot of questions. Here are some answers to get you started!