cmake/Modules/FindGRPC.cmake

option(ENABLE_GRPC_REFLECTION "Link to gRPC Reflection library" OFF)

# FIXME(kirillbobyrev): Check if gRPC and Protobuf headers can be included at
# configure time.
find_package(Threads REQUIRED)

# Prefer finding gPRC through CMakeConfig and a hint can be provided via
# GRPC_INSTALL_PATH. This requires gRPC to be built and installed
# to ${GRPC_INSTALL_PATH} via -DCMAKE_INSTALL_PREFIX=${GRPC_INSTALL_PATH}.
# Libraries will be linked according to gRPC build policy which generates
# static libraries when BUILD_SHARED_LIBS is Off and dynamic libraries when
# it's On (NOTE: This is a variable passed to gRPC CMake build invocation,
# LLVM's BUILD_SHARED_LIBS has no effect).
# Package managers like Homebrew will also install Config.cmake and user can
# specify GRPC_INSTALL_PATH or CMAKE_PREFIX_PATH to locate installed package.
set(protobuf_MODULE_COMPATIBLE TRUE)
find_package(Protobuf CONFIG HINTS ${GRPC_INSTALL_PATH})
message(STATUS "Using protobuf ${Protobuf_VERSION}")
# There's a `c-ares` library whose CMake file sets the `PACKAGE_VERSION` variable.
# Preserve the original `PACKAGE_VERSION` value and restore it.
set(PACKAGE_VERSION_PREV "${PACKAGE_VERSION}")
find_package(gRPC CONFIG HINTS ${GRPC_INSTALL_PATH})
set(PACKAGE_VERSION "${PACKAGE_VERSION_PREV}")
message(STATUS "Using gRPC ${gRPC_VERSION}")

if (Protobuf_FOUND AND gRPC_FOUND)
  # gRPC CMake CONFIG gives the libraries slightly odd names, make them match
  # the conventional system-installed names.
  set_target_properties(protobuf::libprotobuf PROPERTIES IMPORTED_GLOBAL TRUE)
  add_library(protobuf ALIAS protobuf::libprotobuf)
  set_target_properties(gRPC::grpc++ PROPERTIES IMPORTED_GLOBAL TRUE)
  add_library(grpc++ ALIAS gRPC::grpc++)
  if (ENABLE_GRPC_REFLECTION)
    set_target_properties(gRPC::grpc++_reflection PROPERTIES IMPORTED_GLOBAL TRUE)
    add_library(grpc++_reflection ALIAS gRPC::grpc++_reflection)
  endif()

  set(GRPC_CPP_PLUGIN $<TARGET_FILE:gRPC::grpc_cpp_plugin>)
  set(PROTOC ${Protobuf_PROTOC_EXECUTABLE})
else()
  # Now fallback to system-installed gRPC and ProtoBuf.
  # We always link dynamically in this mode. While the static libraries are
  # usually installed, the CMake files telling us *which* static libraries to
  # link are not.
  # FIXME: this path should not work on newer grpc versions and should be
  # removed in favor of `find_package` implementation.
  if (NOT BUILD_SHARED_LIBS)
    message(NOTICE "gRPC and Protobuf will be linked dynamically. If you want static linking, build gRPC from sources with -DBUILD_SHARED_LIBS=Off.")
  endif()
  find_program(GRPC_CPP_PLUGIN grpc_cpp_plugin)
  find_program(PROTOC protoc)
  if (NOT GRPC_CPP_PLUGIN OR NOT PROTOC)
    message(FATAL_ERROR "gRPC C++ Plugin and Protoc must be on $PATH for gRPC-enabled build.")
  endif()
  if(NOT TARGET grpc++)
    find_library(GRPC_LIBRARY grpc++ REQUIRED)
    add_library(grpc++ UNKNOWN IMPORTED GLOBAL)
    message(STATUS "Using grpc++: " ${GRPC_LIBRARY})
    set_target_properties(grpc++ PROPERTIES IMPORTED_LOCATION ${GRPC_LIBRARY})
    if (ENABLE_GRPC_REFLECTION)
      find_library(GRPC_REFLECTION_LIBRARY grpc++_reflection REQUIRED)
      add_library(grpc++_reflection UNKNOWN IMPORTED GLOBAL)
      set_target_properties(grpc++_reflection PROPERTIES IMPORTED_LOCATION ${GRPC_REFLECTION_LIBRARY})
    endif()
    find_library(PROTOBUF_LIBRARY protobuf REQUIRED)
    message(STATUS "Using protobuf: " ${PROTOBUF_LIBRARY})
    add_library(protobuf UNKNOWN IMPORTED GLOBAL)
    set_target_properties(protobuf PROPERTIES IMPORTED_LOCATION ${PROTOBUF_LIBRARY})
  endif()
endif()

if (ENABLE_GRPC_REFLECTION)
  set(REFLECTION_LIBRARY grpc++_reflection)
endif()

# Proto headers are generated in ${CMAKE_CURRENT_BINARY_DIR}.
# Libraries that use these headers should adjust the include path.
# If the "GRPC" argument is given, services are also generated.
# The DEPENDS list should name *.proto source files that are imported.
# They may be relative to the source dir or absolute (for generated protos).
function(generate_proto_sources GeneratedSource ProtoFile)
  cmake_parse_arguments(PARSE_ARGV 2 PROTO "GRPC" "" "DEPENDS")
  get_filename_component(ProtoSourceAbsolutePath "${CMAKE_CURRENT_SOURCE_DIR}/${ProtoFile}" ABSOLUTE)
  get_filename_component(ProtoSourcePath ${ProtoSourceAbsolutePath} PATH)
  get_filename_component(Basename ${ProtoSourceAbsolutePath} NAME_WLE)

  set(GeneratedProtoSource "${CMAKE_CURRENT_BINARY_DIR}/${Basename}.pb.cc")
  set(GeneratedProtoHeader "${CMAKE_CURRENT_BINARY_DIR}/${Basename}.pb.h")
  set(Flags
    --cpp_out="${CMAKE_CURRENT_BINARY_DIR}"
    --proto_path="${ProtoSourcePath}")
  if (PROTO_GRPC)
    list(APPEND Flags
      --grpc_out="${CMAKE_CURRENT_BINARY_DIR}"
      --plugin=protoc-gen-grpc="${GRPC_CPP_PLUGIN}")
    list(APPEND GeneratedProtoSource "${CMAKE_CURRENT_BINARY_DIR}/${Basename}.grpc.pb.cc")
    list(APPEND GeneratedProtoHeader "${CMAKE_CURRENT_BINARY_DIR}/${Basename}.grpc.pb.h")
  endif()
  add_custom_command(
        OUTPUT ${GeneratedProtoSource} ${GeneratedProtoHeader}
        COMMAND ${PROTOC}
        ARGS ${Flags} "${ProtoSourceAbsolutePath}"
        DEPENDS "${ProtoSourceAbsolutePath}")

  set(${GeneratedSource} ${GeneratedProtoSource} PARENT_SCOPE)

  # Ensure dependency headers are generated before dependent protos are built.
  # DEPENDS arg is a list of "Foo.proto". While they're logically relative to
  # the source dir, the generated headers we need are in the binary dir.
  foreach(ImportedProto IN LISTS PROTO_DEPENDS)
    # Foo.proto -> Foo.pb.h
    STRING(REGEX REPLACE "\\.proto$" ".pb.h" ImportedHeader "${ImportedProto}")
    # Foo.pb.h -> ${CMAKE_CURRENT_BINARY_DIR}/Foo.pb.h
    get_filename_component(ImportedHeader "${ImportedHeader}"
      ABSOLUTE
      BASE_DIR "${CMAKE_CURRENT_BINARY_DIR}")
    # Compilation of each generated source depends on ${BINARY}/Foo.pb.h.
    foreach(Generated IN LISTS GeneratedProtoSource)
      # FIXME: CMake docs suggest OBJECT_DEPENDS isn't needed, but I can't get
      #        the recommended add_dependencies() approach to work.
      set_source_files_properties("${Generated}"
        PROPERTIES OBJECT_DEPENDS "${ImportedHeader}")
    endforeach(Generated)
  endforeach(ImportedProto)
endfunction()