1，获取代码

mkdir dart-sdk
cd dart-sdk
fetch dart

使用fetch dart命令会在目录下生成.gclient文件：

solutions = [
  {
    "name": "sdk",
    "url": "https://dart.googlesource.com/sdk.git",
    "deps_file": "DEPS",
    "managed": False,
    "custom_deps": {},
  },
]

疑惑：与flutter engine 构建时候通过gclient sync同步的dart sdk有什么区别？

flutter engine构建时用gclient sync下载的dart sdk依赖与fetch dart获取有不同，缺少buildtools/gn，通过下面可以验证：

拷贝/Volumes/huc/dartvm/flutter_engine/src/third_party/dart到/Volumes/huc/dartvm/dart-sdk-copy/sdk，目录名改为sdk
cd 到sdk执行编译命令

huchu58:sdk huchu$ ./tools/build.py --no-goma --mode release --arch x64 create_sdk
Traceback (most recent call last):
  File "/Volumes/huc/dartvm/dart-sdk-copy/sdk/./tools/build.py", line 308, in <module>
    sys.exit(Main())
  File "/Volumes/huc/dartvm/dart-sdk-copy/sdk/./tools/build.py", line 257, in Main
    gn_py.RunGnOnConfiguredConfigurations(options)
  File "/Volumes/huc/dartvm/dart-sdk-copy/sdk/tools/gn.py", line 582, in RunGnOnConfiguredConfigurations
    BuildGnCommand(args, mode, arch, target_os, sanitizer,
  File "/Volumes/huc/dartvm/dart-sdk-copy/sdk/tools/gn.py", line 556, in BuildGnCommand
    raise Exception("Couldn't find the gn binary at path: " + gn)
Exception: Couldn't find the gn binary at path: /Volumes/huc/dartvm/dart-sdk-copy/sdk/buildtools/gn

可以看到，直接从dart sdk下载的源代码是没有build相关的资源配置文件的。是无法准备编译的。

2，编译

构建64位

cd sdk
./tools/build.py --no-goma --mode release --arch x64 create_sdk

构建arm64

./tools/build.py --no-goma -m release -a arm64 -t  create_sdk

构建vm

./tools/build.py --no-goma -m release -a arm64 runtime

疑惑：与flutter engine 构建时候通过 --no-prebuilt-dart-sdk指定编译dart sdk，./flutter/tools/gn --unoptimized --no-prebuilt-dart-sdk编译的dart sdk有什么区别？

3，测试

测试之前构建的内容：

 ./tools/build.py --no-goma --mode release --arch arm64

4，有什么用

输出在

out/ReleaseX64/dart-sdk