CMake INTERFACE_LINK_LIBRARIES entries get decorated - cmake

Question

I recently did some CMake cleanup on a library I have, the main change being that instead of exporting my targets to a config file directly. At the same time I wanted to move adding the target to the toplevel CMakeLists.txt and then just add sources to that single target as I recurse down into subdirectories.
So I have the toplevel CMakelists.txt that contains:
add_library(Foo "")
add_library(Bar::Foo ALIAS Foo)
add_subdirectory(src)
in src the CMakeLists.txt has
add_subdirectory(Buz)
add_subdirectory(Fuz)
in Fuz the CMakeLists.txt has
target_sources(Foo
PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/FooSource.hpp>
$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}/FooSource.hpp>
PRIVATE
FooSource.cpp
)
target_include_directories(Foo
PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>
$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}>
)
target_link_libraries(Foo
PUBLIC
Bar::Buz # target from first sub dir add...eventually to be merged in like manner
PRIVATE
avcodec
avformat
avutil
swscale
)
Before the change the resulting FooConfig.cmake that would be installed would contain these lines:
set_target_properties(Foo::Foo PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include/Foo/klv_parser;${_IMPORT_PREFIX}/include/Foo/frame_source"
INTERFACE_LINK_LIBRARIES "\$<LINK_ONLY:avcodec>;\$<LINK_ONLY:avformat>;\$<LINK_ONLY:avutil>;\$<LINK_ONLY:swscale>;\$<LINK_ONLY:Foo::foo_common>"
INTERFACE_SOURCES "${_IMPORT_PREFIX}/include/Foo/klv_parser/KlvParser.hpp;${_IMPORT_PREFIX}/include/Foo/frame_source/FrameSource.hpp"
where the LINK_ONLY libraries are ones I listed as PRIVATE in a target_link_libraries. However since the change, these private libraries have been decorated with a seemingly random hex number:
set_target_properties(Foo::Foo PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include/Foo/klv_parser;${_IMPORT_PREFIX}/include/Foo/frame_source"
INTERFACE_LINK_LIBRARIES "\$<LINK_ONLY:avcodec::#<0x2aaeb30>>;\$<LINK_ONLY:avformat::#<0x2aaeb30>>;\$<LINK_ONLY:avutil::#<0x2aaeb30>>;\$<LINK_ONLY:swscale::#<0x2aaeb30>>;\$<LINK_ONLY:Foo::foo_common::#<0x2aaeb30>>"
INTERFACE_SOURCES "${_IMPORT_PREFIX}/include/Foo/klv_parser/KlvParser.hpp;${_IMPORT_PREFIX}/include/Foo/frame_source/FrameSource.hpp"
)
Libraries in the PUBLIC section of target_link_libraries are not decorated--only ones in the PRIVATE section are.
I've been able to narrow it down to moving the add_library command to a higher level directory. i.e. if my CMakeLists.txt in the Fuz directory has:
add_library(Foo "")
add_library(Bar::Foo ALIAS Foo)
target_sources(Foo
PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/FooSource.hpp>
$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}/FooSource.hpp>
PRIVATE
FooSource.cpp
)
target_include_directories(Foo
PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>
$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}>
)
target_link_libraries(Foo
PUBLIC
Bar::Buz # target from first sub dir add...eventually to be merged in like manner
PRIVATE
avcodec
avformat
avutil
swscale
)
(and no add_library commands are in the top level CMakeLists.txt) they all works as it should. But if the only change I make is to move the two lines
add_library(Foo "")
add_library(Bar::Foo ALIAS Foo)
to either the toplevel CMakeLists.txt or even the one in src then this weird decoration occurs. To me this really seems like a bug in CMake, but maybe not?
I'm using CMake 3.15.5 on Ubuntu 18.04. Full minimal example is here: https://github.com/jasonbeach/cmake_bug.git

Answer 1

This appears to be a bug within CMake. I was originally using CMake 3.15.5 and in the course of troubleshooting, updated to CMake 3.19.6 and it started working as it should. It appears to have been fixed somewhere in there.