Windows下Bazel调用MSYS2时无法找到g++的求助

我通过Chocolatey在Windows系统上安装了Bazel，同时安装MSYS2以获取bash.exe环境。已通过MSYS2的pacman工具安装g并将其添加至系统PATH，在MSYS2 shell及原生Powershell中执行g++ --version均正常，但通过Bazel执行构建命令时，却出现g未找到的错误，具体报错如下：

C:/> bazel build //kernels:rasterize_triangles_kernel
INFO: Analyzed target //kernels:rasterize_triangles_kernel (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
ERROR: C://kernels/BUILD:20:8: Executing genrule //kernels:rasterize_triangles_kernel failed: (Exit 127): bash.exe failed: error executing command (from target //kernels:rasterize_triangles_kernel) C:\msys64\usr\bin\bash.exe -c ... (remaining 1 argument skipped)
/usr/bin/bash: line 1: g++: command not found
Target //kernels:rasterize_triangles_kernel failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 4.883s, Critical Path: 4.80s
INFO: 2 processes: 2 internal.
FAILED: Build did NOT complete successfully

可行的解决方法 #

• 在genrule中显式指定PATH或g++绝对路径
  如果是自定义genrule，要么直接把命令里的g++替换为MSYS2中g++的绝对路径（比如C:/msys64/usr/bin/g++.exe），要么在cmd开头先添加MSYS2的bin目录到PATH：

  genrule(
      name = "rasterize_triangles_kernel",
      srcs = [...],
      outs = [...],
      cmd = "export PATH=/usr/bin:$PATH && g++ [你的编译参数]",
      tools = [...],
  )
  

• 让Bazel继承当前环境的完整PATH
  Bazel默认会隔离构建环境，可能不会完全读取系统PATH。执行构建时可以用参数强制继承当前环境的PATH：

  bazel build //kernels:rasterize_triangles_kernel --action_env=PATH="$env:PATH"
  

  也可以在执行Bazel命令前，手动把MSYS2的bin目录放到PATH最前端，避免路径优先级问题：

  $env:PATH = "C:\msys64\usr\bin;" + $env:PATH
  bazel build //kernels:rasterize_triangles_kernel
  

• 配置Bazel自定义C++工具链
  创建工具链配置文件指定MSYS2的编译器路径，比如新建toolchain.bzl：

  def _msys2_cc_toolchain_impl(ctx):
      toolchain = cc_common.create_cc_toolchain_config_info(
          ctx = ctx,
          toolchain_identifier = "msys2-gcc",
          host_system_name = "x64_windows",
          target_system_name = "x64_windows",
          target_cpu = "x86_64",
          compiler = "gcc",
          tool_paths = {
              "gcc": "C:/msys64/usr/bin/g++.exe",
              "g++": "C:/msys64/usr/bin/g++.exe",
              "ld": "C:/msys64/usr/bin/ld.exe",
              "ar": "C:/msys64/usr/bin/ar.exe",
          },
      )
      return [toolchain]
  
  msys2_cc_toolchain = rule(
      implementation = _msys2_cc_toolchain_impl,
      provides = [CcToolchainConfigInfo],
  )
  

  之后在WORKSPACE中注册该工具链，或构建时用--crosstool_top参数指定使用这个工具链。

内容的提问来源于stack exchange，提问作者Zoom