CMake error: found relative path while evaluating include directories of

Question

I'm trying to understand why CMake is complaining in a given situation.

I have module A depending on module B which depends on module C.

Module C is a subdir of module B, and the pertinent parts of each module's CMakeLists.txt are as shown here:

module A does:

add_library(A STATIC "")

target_include_directories(A PRIVATE 
    $
)

module B does:

add_library(B static "")

set(some_dirs
  C
)

foreach(DIR ${some_dirs})
  add_subdirectory(${DIR})
  target_link_libraries(B PUBLIC ${DIR})
endforeach(DIR)

module C does:

add_library(C STATIC "")

target_include_directories(C
  PUBLIC 
    $
  PRIVATE
)

There is an executable that links against module A.

The reason for the use of TARGET_PROPERTY:INCLUDE_DIRECTORIES is that I am moving a large project with a lot of circular dependencies from a monolithic executable to one with distinct libraries. My initial effort is just to create the modules, then later to break the circular dependencies. So in this example, rather than target_link_libraries on the dependency, I use target_include_directories with the property INCLUDE_DIRECTORIES for the dependencies. I hope that makes sense.

I get an error with the above situation that includes:

Configuring done
Failed to parse JSON from CMake server.
Failed to parse JSON from CMake server.
CMake Error in A/CMakeLists.txt:
  Found relative path while evaluating include directories of
  "A":

followed by some garbage characters and some more "Failed to parse JSON from CMake server lines.

However, when I modify module C to the following:

add_library(C STATIC "")

target_include_directories(C
  PUBLIC 
  PRIVATE
    $
)

The generation errors go away.

OR If I leave module C as it was originally, but change module B to this (i.e. not link against C):

add_library(B static "")

set(some_dirs
  C
)

foreach(DIR ${some_dirs})
  add_subdirectory(${DIR})
#  target_link_libraries(B PUBLIC ${DIR})
endforeach(DIR)

and A to this:

add_library(A STATIC "")

target_include_directories(A PRIVATE 
    $
    $
)

Then the generation errors also go away.

I don't quite understand why CMake thinks there are relative paths when module C uses PUBLIC vs PRIVATE inclusion. I also don't understand why the problem goes away when I remove C as a dependency of B. I do understand that IMPORTED targets can't have relative paths, but none of my targets are IMPORTED, since they are all defined within the same project.

CMake error: found relative path while evaluating include directories of

0 Answers