# Is it possible to switch compilers for certain parts of a CMakeLists.txt?

**URL:** <https://discourse.cmake.org/t/is-it-possible-to-switch-compilers-for-certain-parts-of-a-cmakelists-txt/15310>\
**Category:** Code\
**Created:** [November 16, 2025, 12:46am UTC](https://discourse.cmake.org/t/is-it-possible-to-switch-compilers-for-certain-parts-of-a-cmakelists-txt/15310 "2025-11-16T00:46:40Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![guest271314](https://discourse.cmake.org/user_avatar/discourse.cmake.org/guest271314/32/5903_2.png) [@guest271314](https://discourse.cmake.org/u/guest271314)\
**Post date:** [November 16, 2025, 12:46am UTC](https://discourse.cmake.org/t/is-it-possible-to-switch-compilers-for-certain-parts-of-a-cmakelists-txt/15310/1 "2025-11-16T00:46:40Z")

</div>

I’m trying to target WASM for a library that was not originally written with compilation to WASM as a goal. The existing CMakeLists.txt builds protobuf and executes protoc. WASM doesn’t have subprocess calls or `<sys/wait.h>`. The build fails at the protobuf build and subprocess calls using WASI-SDK’s `clang++` and Emscripten.

My limited understanding of protobuf is that is builds C++ from templates. My idea is to use some kind of condition to use `g++` or LLVM Project’s `clang++` to do the protobuf stuff while the rest of the build uses WASI-SDK `clang++` or Emsciptens’s `em++`. Is that a reasonable and possible workaround to use as much as the already written build process as possible, while targeting WASM?

This is what I think are causing the WASM compilers to exit with errors

`set(protobuf_INSTALL OFF CACHE BOOL “Install protobuf off” FORCE)`  
`add_subdirectory(third_party/protobuf EXCLUDE_FROM_ALL)`  
`if(APPLE)`  
`execute_process(`  
`COMMAND uname -m`  
`OUTPUT_VARIABLE HOST_ARCH`  
`OUTPUT_STRIP_TRAILING_WHITESPACE`  
`)`  
`set_target_properties(protoc libprotoc libprotobuf`  
`PROPERTIES`  
`OSX_ARCHITECTURES “${HOST_ARCH}”`  
`)`  
`endif()`

and this part

`add_custom_command(`  
`OUTPUT`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/cached_network_parameters.pb.h`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/crypto_server_config.pb.h`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/source_address_token.pb.h`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/cached_network_parameters.pb.cc`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/crypto_server_config.pb.cc`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/source_address_token.pb.cc`  
`DEPENDS protobuf::protoc ${filename} ${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/cached_network_parameters.proto`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/crypto_server_config.proto`  
`${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/source_address_token.proto`  
`COMMAND protobuf::protoc --proto_path=${PROTOMODEL_PATH} --cpp_out=${PROTOBINDING_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/cached_network_parameters.proto`  
`COMMAND protobuf::protoc --proto_path=${PROTOMODEL_PATH} --cpp_out=${PROTOBINDING_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/crypto_server_config.proto`  
`COMMAND protobuf::protoc --proto_path=${PROTOMODEL_PATH} --cpp_out=${PROTOBINDING_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/third_party/quiche/quiche/quic/core/proto/source_address_token.proto`  
`)`