Dependent sibling subdirectories in CMake - c++

Question

My current project has the following structure:
root
|- parser
| |- include // a directory for headers
| |- src // a directory for sources
| |- parser.yy
| |- scanner.ll
| |- CmakeLists.txt
|
|- preprocessor
| |- include // a directory for headers
| |- src // a directory for sources
| |- CmakeLists.txt
|
|- main.cpp
|- CMakeLists.txt
Now I want to start generating assembly codes. I have to use staticstack and codegen (are classes which are going to be defined) in the parser.yy and in srcfolder of the parser foler.
I cannot figure out how to do that.
What's the best practice in CMake to do this ?
Should I make subdirectories named semstack and codegen in parser folder ? This doesn't seem correct to me since as a CMake project gets larger the hierarchy will get deeper and if more dependencies are there then it would be a mess.
Should I make these subdirectories in the root ? If then what is the syntax in CMake to use sibling subdirectory ?

Answer 1

If then what is the syntax in CMake to use sibling subdirectory ?
There is no special syntax for this since normal (i.e. not IMPORTED) targets are global. If you define a library in one subdirectory, it may be used in any other via target_link_libraries.
For instance:
# parser/CMakeLists.txt
add_library(parser ...)
add_library(proj::parser ALIAS parser)
target_include_directories(
parser PRIVATE "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>")
target_link_libraries(
parser PRIVATE proj::semstack proj::codegen)
The code for other subdirectories is similar.
# ./CMakeLists.txt
cmake_minimum_required(VERSION 3.22)
project(proj)
add_subdirectory(semstack)
add_subdirectory(codegen)
add_subdirectory(parser)
add_subdirectory(preprocessor)
add_executable(main main.cpp)
target_link_libraries(
main PRIVATE proj::parser proj::preprocessor)
I create and link to ALIAS targets to avoid a typo in a target name being forwarded to the linker verbatim (names with :: in CMake are always considered targets and this is validated at generation time).