Cmake config is broken.

[FrankXie05]

Hi, I'm one of the maintainers of vcpkg, and we recently received a question about libconfg using cmake.
Issue:
There seems to be this problem with the exported cmake usage after we installed libconfig, it fails to link against libconfig++.
Run command ./vcpkg install libconfig:x64-windows --head and output:

libconfig provides CMake targets:

    # this is heuristically generated, and may not be correct
    find_package(libconfig CONFIG REQUIRED)
    target_link_libraries(main PRIVATE libconfig::libconfig libconfig::libconfig++)

For this reason, I made a patch to separate libconfig and libconfig++.

However, from the code structure, libconfig does not seem to be separated, but is linked to libconfig++.
BUt, it was broken.

libconfig/lib/CMakeLists.txt

Line 144 in 4f13b7f

foreach(target_name libconfig libconfig++)

libconfig/lib/CMakeLists.txt

Line 152 in 4f13b7f

NAMESPACE libconfig::

Reproduce steps:
CMakeLists.txt

cmake_minimum_required(VERSION 3.0)
project(test)
add_executable(main main.cpp)
find_package(libconfig CONFIG REQUIRED)
target_link_libraries(main PRIVATE libconfig::libconfig libconfig::libconfig++)

Error:

CMake Error at CMakeLists.txt:5 (target_link_libraries):
  Target "main" links to:

    libconfig::libconfig++

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.

Related vcpkg issue and PR:
microsoft/vcpkg#30906
microsoft/vcpkg#30980

@hyperrealm

[dg0yt]

This question drags in a lot of vcpkg particularities. More general (microsoft/vcpkg#30980 (comment)), please solve this problem and inconsistency:

Target libconfig++ is in namespace and directory libconfig but in config libconfig++.
This makes the target unreachable.

• find_package(libconfig++) doesn't work.
• find_package(libconfig) doesn't provide the target.

Consistent patterns would be:

• Target libconfig++ is in namespace, config and directory libconfig.
• Target libconfig++ is in namespace, config and directory libconfig++.

I would recommend the first alternative, in particular because they are connected.

[mllusar]

Hey ! Is there any new about this issue ? I really need to use libonfig++ under Cmake with vcpkg.

I'm not an advanced programmer, but it seams that all we need need is to rename the namespace.

[FrankXie05]

@mllusar You can use my PR temporarily microsoft/vcpkg#30980

[dg0yt]

• Target libconfig++ is in namespace, config and directory libconfig.

Implemented in #234.