cmake: Define and use MP_INCLUDE_DIR variable

This is needed to refer to the include directory when the cmake project is not
a top-level project (when it is included with add_subdirectory) because
${CMAKE_SOURCE_DIR}/include will no longer refer to the right location.

This is also nice because the variable can be used in the target_capnp_sources
function and simplify calls to that function.

Author: ryanofsky

CMakeLists.txt

@@ -26,6 +26,8 @@ include("cmake/compat_config.cmake")
 include("cmake/pthread_checks.cmake")
 include(GNUInstallDirs)
 
+set(MP_INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/include")
+
 # Generated C++ preprocessor defines
 configure_file(include/mp/config.h.in "${CMAKE_CURRENT_BINARY_DIR}/include/mp/config.h")
 

cmake/TargetCapnpSources.cmake

@@ -68,7 +68,7 @@ function(target_capnp_sources target include_prefix)
   foreach(capnp_file IN LISTS TCS_UNPARSED_ARGUMENTS)
     add_custom_command(
       OUTPUT ${capnp_file}.c++ ${capnp_file}.h ${capnp_file}.proxy-client.c++ ${capnp_file}.proxy-types.h ${capnp_file}.proxy-server.c++ ${capnp_file}.proxy-types.c++ ${capnp_file}.proxy.h
-      COMMAND Libmultiprocess::mpgen ${CMAKE_CURRENT_SOURCE_DIR} ${include_prefix} ${CMAKE_CURRENT_SOURCE_DIR}/${capnp_file} ${TCS_IMPORT_PATHS}
+      COMMAND Libmultiprocess::mpgen ${CMAKE_CURRENT_SOURCE_DIR} ${include_prefix} ${CMAKE_CURRENT_SOURCE_DIR}/${capnp_file} ${TCS_IMPORT_PATHS} ${MP_INCLUDE_DIR}
       DEPENDS ${capnp_file}
       VERBATIM
     )
@@ -89,7 +89,7 @@ function(target_capnp_sources target include_prefix)
   if(relative_path)
     string(APPEND build_include_prefix "/" "${relative_path}")
   endif()
-  target_include_directories(${target} PUBLIC $<BUILD_INTERFACE:${build_include_prefix}>)
+  target_include_directories(${target} PUBLIC $<BUILD_INTERFACE:${build_include_prefix}> ${MP_INCLUDE_DIR})
 
   if(TARGET Libmultiprocess::multiprocess)
     target_link_libraries(${target} PRIVATE Libmultiprocess::multiprocess)

example/CMakeLists.txt

@@ -7,27 +7,21 @@ include(${PROJECT_SOURCE_DIR}/cmake/TargetCapnpSources.cmake)
 add_executable(mpcalculator
   calculator.cpp
 )
-target_capnp_sources(mpcalculator ${CMAKE_CURRENT_SOURCE_DIR} init.capnp calculator.capnp printer.capnp
-  IMPORT_PATHS ${CMAKE_SOURCE_DIR}/include
-)
+target_capnp_sources(mpcalculator ${CMAKE_CURRENT_SOURCE_DIR} init.capnp calculator.capnp printer.capnp)
 target_include_directories(mpcalculator PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
 target_link_libraries(mpcalculator PRIVATE Threads::Threads)
 
 add_executable(mpprinter
   printer.cpp
 )
-target_capnp_sources(mpprinter ${CMAKE_CURRENT_SOURCE_DIR} init.capnp calculator.capnp printer.capnp
-  IMPORT_PATHS ${CMAKE_SOURCE_DIR}/include
-)
+target_capnp_sources(mpprinter ${CMAKE_CURRENT_SOURCE_DIR} init.capnp calculator.capnp printer.capnp)
 target_include_directories(mpprinter PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
 target_link_libraries(mpprinter PRIVATE Threads::Threads)
 
 add_executable(mpexample
   example.cpp
 )
-target_capnp_sources(mpexample ${CMAKE_CURRENT_SOURCE_DIR} init.capnp calculator.capnp printer.capnp
-  IMPORT_PATHS ${CMAKE_SOURCE_DIR}/include
-)
+target_capnp_sources(mpexample ${CMAKE_CURRENT_SOURCE_DIR} init.capnp calculator.capnp printer.capnp)
 target_include_directories(mpexample PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
 target_link_libraries(mpexample PRIVATE Threads::Threads)
 target_link_libraries(mpexample PRIVATE stdc++fs)

test/CMakeLists.txt

@@ -24,9 +24,7 @@ if(BUILD_TESTING AND TARGET CapnProto::kj-test)
     mp/test/test.cpp
   )
   include(${PROJECT_SOURCE_DIR}/cmake/TargetCapnpSources.cmake)
-  target_capnp_sources(mptest ${CMAKE_CURRENT_SOURCE_DIR} mp/test/foo.capnp
-    IMPORT_PATHS ${CMAKE_SOURCE_DIR}/include
-  )
+  target_capnp_sources(mptest ${CMAKE_CURRENT_SOURCE_DIR} mp/test/foo.capnp)
   target_include_directories(mptest PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
   target_link_libraries(mptest PRIVATE CapnProto::kj-test)
   target_link_libraries(mptest PRIVATE Threads::Threads)