build a protoc binary to use to ensure version compat

components/protobuf/functions.cmake

@@ -1,4 +1,38 @@
-find_program(PROTOC protoc)
+if(NOT CMAKE_SCRIPT_MODE_FILE)
+
+set(PROTOBUF_DIR ${CMAKE_CURRENT_LIST_DIR}/protobuf)
+
+set(PROTOBUF_BUILD ${PROJECT_BINARY_DIR}/protobuf-build)
+set(PROTOBUF_BINARY ${PROJECT_BINARY_DIR}/protobuf-binary)
+set(PROTOBUF_SRC ${PROJECT_BINARY_DIR}/protobuf-src)
+
+configure_file(${CMAKE_CURRENT_LIST_DIR}/protobuf-CMakeLists.cmake ${PROTOBUF_BUILD}/CMakeLists.txt)
+if(NOT CMAKE_GENERATOR)
+    set(CMAKE_GENERATOR "Ninja")
+endif()
+execute_process(COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" .
+        RESULT_VARIABLE result
+        WORKING_DIRECTORY ${PROTOBUF_BUILD} )
+if(result)
+    message(FATAL_ERROR "CMake step for protobuf failed: ${result}")
+endif()
+# execute_process(COMMAND ${CMAKE_COMMAND} --build .
+#         RESULT_VARIABLE result
+#         WORKING_DIRECTORY ${PROTOBUF_BUILD})
+# if(result)
+#     message(FATAL_ERROR "Build step for protobuf failed: ${result}")
+# endif()
+
+set(PROTOC ${PROTOBUF_BINARY}/protoc)
+
+add_custom_command(OUTPUT ${PROTOC}
+    COMMENT "Building protoc binary"
+    COMMAND ${CMAKE_COMMAND} --build .
+    USES_TERMINAL
+    WORKING_DIRECTORY ${PROTOBUF_BUILD})
+endif()
+
+# find_program(PROTOC protoc PATHS ${CMAKE_CURRENT_LIST_DIR}/protobuf/cmake/build/)
 
 function(proto_generate_cpp PROTO_FILE PB_OUT HDR_VAR SRC_VAR)
     get_filename_component(PROTO_FILE_NAME ${PROTO_FILE} NAME_WE)
@@ -14,7 +48,7 @@ function(proto_generate_cpp PROTO_FILE PB_OUT HDR_VAR SRC_VAR)
                 --cpp_out=${PB_OUT}
                 --proto_path ${PROTO_FILE_DIR}
                 ${PROTO_FILE_PATH}
-            DEPENDS ${PROTO_FILE_PATH}
+            DEPENDS ${PROTO_FILE_PATH} ${PROTOC}
             COMMENT "Generating nanopb sources for ${PROTO_FILE}")
         set_property(SOURCE ${PROTO_HDR} ${PROTO_SRC} PROPERTY GENERATED TRUE)
         set_property(DIRECTORY . APPEND PROPERTY ADDITIONAL_MAKE_CLEAN_FILES ${PROTO_HDR} ${PROTO_SRC})

components/protobuf/protobuf-CMakeLists.cmake

@@ -0,0 +1,17 @@
+cmake_minimum_required(VERSION 2.8.2)
+
+project(protobuf-build NONE)
+
+include(ExternalProject)
+ExternalProject_Add(protobuf
+  URL               "${PROTOBUF_DIR}"
+  SOURCE_DIR        "${PROTOBUF_SRC}"
+  BINARY_DIR        "${PROTOBUF_BINARY}"
+  SOURCE_SUBDIR     "cmake"
+  CMAKE_GENERATOR   "${CMAKE_GENERATOR}"
+  CMAKE_ARGS        -Dprotobuf_BUILD_TESTS:BOOL=OFF
+  INSTALL_COMMAND   ""
+  TEST_COMMAND      ""
+  USES_TERMINAL_CONFIGURE ON
+  USES_TERMINAL_BUILD ON
+)