在以外部库形式源码引入tRPC，使用Ninja作为生成器时存在两次生成trpc_options.pb.cc/trpc_cpp_options.pb.cc的行为

[deadlinefen]

我在按照文档https://github.com/trpc-group/trpc-cpp/blob/main/docs/zh/bazel_or_cmake.md
使用CMake与Ninja，将tRPC以外部库形式源码引入项目时报错：

CMake Error:
  Running

   '/usr/local/bin/ninja' '-C' '/data/workspace/bld' '-t' 'recompact'

  failed with:

   ninja: error: build.ninja:11818: multiple rules generate ../cmake-third-party/trpc-cpp/trpc/proto/trpc_options.pb.cc

之后我检查了build.ninja，发现其中有两处生成trpc_options.pb.cc与trpc_cpp_options.pb.cc的命令（以trpc_cpp_options.pb.cc为例）：

# 4902行处
# Custom command for ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc

build ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h | ${cmake_ninja_workdir}../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc ${cmake_ninja_workdir}../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h: CUSTOM_COMMAND ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.proto || _deps/trpc-cpp-build/cmake_third_party/gflags/libgflags_nothreads.a _deps/trpc-cpp-build/trpc/tools/trpc_cpp_plugin/bin/trpc_cpp_plugin bin/protoc lib/libflatbuffers.a lib/libgmock.a lib/libgtest.a lib/libjsoncpp.a lib/liblz4.a lib/libnghttp2_static.a lib/libprotobuf.a lib/libprotoc.a lib/libsnappy.a lib/libyaml-cpp.a
  COMMAND = cd /data/workspace/cmake-third-party/trpc-cpp && /data/workspace/bld/bin/protoc -I /data/workspace/cmake-third-party/trpc-cpp -I /data/workspace/cmake-third-party/trpc-cpp/cmake_third_party/protobuf/src --cpp_out=. trpc/tools/comm/trpc_cpp_options.proto
  DESC = Generating ../../../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc, ../../../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h
  restat = 1

# 11821行处
# Custom command for ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc

build ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h | ${cmake_ninja_workdir}../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc ${cmake_ninja_workdir}../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h: CUSTOM_COMMAND ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.proto || bin/protoc lib/libprotobuf.a lib/libprotoc.a
  COMMAND = cd /data/workspace/cmake-third-party/trpc-cpp && /data/workspace/bld/bin/protoc -I /data/workspace/cmake-third-party/trpc-cpp -I /data/workspace/cmake-third-party/trpc-cpp/cmake_third_party/protobuf/src --cpp_out=. trpc/tools/comm/trpc_cpp_options.proto
  DESC = Generating ../../../../../../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc, ../../../../../../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h
  restat = 1

经检查貌似是这两个文件同时被cmake_object_order_depends_target_trpc与cmake_object_order_depends_target_trpc_cpp_plugin依赖导致的。ninja.build中的依赖关系如下：

# Order-only phony target for trpc

build cmake_object_order_depends_target_trpc: phony || ../cmake-third-party/trpc-cpp/trpc/codec/trpc/trpc.pb.cc ../cmake-third-party/trpc-cpp/trpc/codec/trpc/trpc.pb.h ../cmake-third-party/trpc-cpp/trpc/proto/trpc.pb.cc ../cmake-third-party/trpc-cpp/trpc/proto/trpc.pb.h ../cmake-third-party/trpc-cpp/trpc/proto/trpc_options.pb.cc ../cmake-third-party/trpc-cpp/trpc/proto/trpc_options.pb.h ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h ../cmake-third-party/trpc-cpp/trpc/trpc.pb.cc ../cmake-third-party/trpc-cpp/trpc/trpc.pb.h _deps/trpc-cpp-build/trpc/tools/trpc_cpp_plugin/bin/trpc_cpp_plugin bin/protoc cmake_object_order_depends_target_flatbuffers cmake_object_order_depends_target_gflags_nothreads_static cmake_object_order_depends_target_gmock cmake_object_order_depends_target_gtest cmake_object_order_depends_target_jsoncpp_lib cmake_object_order_depends_target_libprotobuf cmake_object_order_depends_target_libprotoc cmake_object_order_depends_target_lz4_static cmake_object_order_depends_target_nghttp2_static cmake_object_order_depends_target_snappy cmake_object_order_depends_target_yaml-cpp

# Order-only phony target for trpc_cpp_plugin

build cmake_object_order_depends_target_trpc_cpp_plugin: phony || ../cmake-third-party/trpc-cpp/trpc/proto/trpc_options.pb.cc ../cmake-third-party/trpc-cpp/trpc/proto/trpc_options.pb.h ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.cc ../cmake-third-party/trpc-cpp/trpc/tools/comm/trpc_cpp_options.pb.h bin/protoc cmake_object_order_depends_target_libprotobuf cmake_object_order_depends_target_libprotoc

使用CMake+Make就不会有上述问题。

CMake版本3.22.1
Ninja版本1.12.1
Make版本4.3