流程

1. 项目根目录下新增.gclient和.gclient_entries

//.gclient
solutions = [{"name": "src","url": "","managed": False,"custom_deps": {},"custom_vars": {},},
]// .gclient_entries
entries = {'src': '',
}

gclient是一个多仓管理工具，可以把多个仓库的源码clone到本地的一个项目中，具体可以看2. chromium开发工具--gclient - Bigben - 博客园

2. 新建并进入src目录

3. 新建示例代码hello_world.cc

#include <iostream>
using namespace std;int main()
{cout<< "hello world" << endl;while(1) {} // 为了让窗口不要自动关闭，好看到输出结果return 0;
}

4 新建.gn，该文件指出了gn的配置文件路径，以及使用哪个python解释器。

buildconfig = "//build/config/BUILDCONFIG.gn"# The python interpreter to use by default. On Windows, this will look
# for python3.exe and python3.bat.
script_executable = "python3"

5. 新建BULD.gn，这个文件指出我们该如何形成可执行文件

executable("hello_world") {sources = ["hello-world.cc",]
}

6. 新建build/config/BUILDCONFIG.gn，把chromuim源码下对应文件粘过来，因为我只想研究一下核心流程，不考虑兼容性，所以我把default_compiler_configs及以后的代码全删了，不然要复制太多文件了。

7. 运行gn gen out/default，out/后文件名可以任意，但是out/这个前缀不能修改。

8. 报错gn.py: Could not find checkout in any parent of the current path。原因是src目录下缺少buildtools，把chromium/src/buildtools复制到<your project>/src/buildtools即可。

9. 接下来会报一堆缺少文件的错误，这些文件分别在src/build、src/build_overrides、src/buildtools、src/tools四个目录下，你可以试着把这几个文件夹一次性从chromium项目下拷贝过来，我当时只拷了build文件夹所以报错了，而且没报具体错误原因所以没法排查，最后是缺哪个文件拷哪个文件一点点拷完了，rust相关代码我不想复制了，所以引用到的地方我就全删了。

10. gn gen out/default后，运行

autoninja -C out/default

这时候会报错depot_tools/ninja.py: Could not find Ninja in the third_party of the current project, nor in your PATH，原因就是ninja.exe既不在当前项目下，也不在环境变量里。

解决方案：在src目录下新建third_party，把chromium项目中的third_party/ninja复制过去。

11. 再次运行autoninja -C out/default，报错The system cannot find the file specified.

把chromium项目third_party目录下llvm-build\Release+Asserts\bin\clang-cl.exe复制过来，再次运行命令就可以成功了。

12. 双击out/default/hello_world.exe，显示

证明构建成功了。

问题汇总

问题一：gn.py: Could not find checkout in any parent of the current path.

核心原因：缺少buildtools。

解决方案：把chromium/src/buildtools复制到<your project>/src/buildtools，进入src目录后执行命令

gn gen out/default

.gclient和.gclient_entries文件最好也加上，虽然gclient_paths.py脚本中做了兼容，如果命令行所在目录下存在buildtools，就返回当前目录作为入口，但这毕竟不是一种规范的做法。

问题二：could not execute interpreter

根目录下的.gn文件需要设置script_executable，否则gn会直接执行py文件，windows环境下会在环境变量path中寻找python.exe和python.bat，没找到就会报错。

# The python interpreter to use by default. On Windows, this will look
# for python3.exe and python3.bat.
script_executable = "python3"

具体逻辑看gn源码src\gn\setup.cc

大致就是先查当前目录下是否存在python3.exe，存在就返回绝对路径。

否则查找环境变量path下是否存在python3.exe，和python3.bat；如果存在python3.exe，返回对应绝对路径，存在python3.bat，就通过该文件找到对应的python3.exe，返回exe的绝对路径。

否则返回空路径。

// python_exe_name and python_bat_name can be empty but cannot be absolute
// paths. They should be "python.exe" or "", etc., and "python.bat" or "", etc.
base::FilePath FindWindowsPython(const base::FilePath& python_exe_name,const base::FilePath& python_bat_name) {char16_t current_directory[MAX_PATH];::GetCurrentDirectory(MAX_PATH, reinterpret_cast<LPWSTR>(current_directory));// First search for python.exe in the current directory.if (!python_exe_name.empty()) {CHECK(python_exe_name.FinalExtension() == u".exe");CHECK_EQ(python_exe_name.IsAbsolute(), false);base::FilePath cur_dir_candidate_exe =base::FilePath(current_directory).Append(python_exe_name);if (base::PathExists(cur_dir_candidate_exe))return cur_dir_candidate_exe;}// Get the path.const char16_t kPathEnvVarName[] = u"Path";DWORD path_length = ::GetEnvironmentVariable(reinterpret_cast<LPCWSTR>(kPathEnvVarName), nullptr, 0);if (path_length == 0)return base::FilePath();std::unique_ptr<char16_t[]> full_path(new char16_t[path_length]);DWORD actual_path_length = ::GetEnvironmentVariable(reinterpret_cast<LPCWSTR>(kPathEnvVarName),reinterpret_cast<LPWSTR>(full_path.get()), path_length);CHECK_EQ(path_length, actual_path_length + 1);// Search for python.exe in the path.for (const auto& component : base::SplitStringPiece(std::u16string_view(full_path.get(), path_length), u";",base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY)) {if (!python_exe_name.empty()) {base::FilePath candidate_exe =base::FilePath(component).Append(python_exe_name);if (base::PathExists(candidate_exe))return candidate_exe;}// Also allow python.bat, but convert into the .exe.if (!python_bat_name.empty()) {CHECK(python_bat_name.FinalExtension() == u".bat");CHECK_EQ(python_bat_name.IsAbsolute(), false);base::FilePath candidate_bat =base::FilePath(component).Append(python_bat_name);if (base::PathExists(candidate_bat)) {base::FilePath python_exe = PythonBatToExe(candidate_bat);if (!python_exe.empty())return python_exe;}}}return base::FilePath();
}

问题三：depot_tools/ninja.py: Could not find Ninja in the third_party of the current project, nor in your PATH

解决方案，要么添加指向ninja.exe的path，要么就在项目里添加third_party/ninja.exe

def main(args):# ...# Get gclient root + src.primary_solution_path = gclient_paths.GetPrimarySolutionPath()gclient_root_path = gclient_paths.FindGclientRoot(os.getcwd())gclient_src_root_path = Noneif gclient_root_path:gclient_src_root_path = os.path.join(gclient_root_path, "src")for base_path in set(# 这三个目录下只要有一个存在/third_party/ninja.exe就行[primary_solution_path, gclient_root_path, gclient_src_root_path]):if not base_path:continueninja_path = os.path.join(base_path,"third_party","ninja","ninja" + gclient_paths.GetExeSuffix(),)if os.path.isfile(ninja_path):check_out_dir(args[1:])return subprocess.call([ninja_path] + args[1:])return fallback(args[1:]) #这个函数会在环境变量中找ninja.exe，还没找到就会打印报错信息了