How do I properly import, into a parent CMake project, a Protobuf-generated .h file created in a dependency CMake project?

Question

Here is what my project hierarchy looks like (simplified):

+-- CMakeLists.txt
+-- party
|   +-- CMakeLists.txt
|   +-- include
|   \-- src
|       \-- party.cc
\-- super
    +-- CMakeLists.txt
    +-- include
    |   \-- super.h
    \-- src
        +-- super.cc
        \-- super.proto

I have a library CMake project, called Super, that has some Google Protobuf code in it. A source file, super.proto , is used by the protoc compiler to create super.pb.cc and super.pb.h . Super's CMakeLists.txt looks like this:

cmake_minimum_required(VERSION 3.1)
project(Super)
find_package(Protobuf REQUIRED)

set(INCLUDE_DIR "include")
set(SRC_DIR "src")

add_definitions("-std=c++11")

include_directories(${CMAKE_CURRENT_BINARY_DIR})
include_directories(${INCLUDE_DIR})
include_directories(${PROTOBUF_INCLUDE_DIRS})

# === Super library ===
PROTOBUF_GENERATE_CPP(super_proto_srcs super_proto_incl ${SRC_DIR}/super.proto)
file(GLOB shared_srcs "${SRC_DIR}/*.cc")
add_library(super SHARED ${shared_srcs} ${super_proto_srcs})
target_link_libraries(super ${PROTOBUF_LIBRARIES})

# === Install and exports ===
set(${PROJECT_NAME}_INCLUDE_DIRS
    ${PROJECT_SOURCE_DIR}/include
    CACHE INTERNAL "${PROJECT_NAME}: Include Directories" FORCE)

Super is to become a shared library named libsuper.so . It has a header file that depends on super.pb.h .

Party is a binary that uses libsuper.so . It doesn't care about Protobuf, at least not directly. It includes super.h and calls its method. Party has a CMakeLists.txt that looks like this:

cmake_minimum_required(VERSION 3.1)
project(Party)

set(INCLUDE_DIR "include")
set(SRC_DIR "src")

add_definitions("-std=c++11")

include_directories(${INCLUDE_DIR})
include_directories(${Super_INCLUDE_DIRS})

# === Party binary ===
file(GLOB binary_srcs "${SRC_DIR}/*.cc")
add_executable(party ${binary_srcs})
target_link_libraries(party super)

At the level of the parent directory, the unifying CMakeLists.txt looks like this:

cmake_minimum_required(VERSION 3.1)
project(SuperParty)

add_subdirectory(super)
add_subdirectory(party)

I can build Super on its own with no errors. The Protobuf-generated files are created, also libsuper.so . However, when I try to build the master project, SuperParty, I get the following error:

In file included from superparty/party/src/party.cc:1:0:
superparty/super/include/super.h:1:22: fatal error: super.pb.h: No such file or directory

The file exists in SuperParty's build/ directory, called build/super/super.pb.h . My problem is that I need to tell Party to include this auto-generated file, but I don't know where to get that file's path so that I can create the appropriate line in Party's CMakeLists.txt . Party effectively needs a reference to the CMAKE_BINARY_PATH that the master project is using.

Answer 1

Turns out there's an automatic variable created named Super_BINARY_DIR that I could use in Party's CMakeLists.txt , but there is, in fact, an even better way to do it. Instead of modifying Party, which was already getting its list of includes from Super_INCLUDE_DIRS , I added a CMAKE_CURRENT_BINARY_DIR to the list of includes that Super created for Party to use. Here is the new ending to Super's CMakeLists.txt :

# === Install and exports ===
set(${PROJECT_NAME}_INCLUDE_DIRS
    ${CMAKE_CURRENT_BINARY_DIR}
    ${PROJECT_SOURCE_DIR}/include
    CACHE INTERNAL "${PROJECT_NAME}: Include Directories" FORCE)