[1.9.6 regression] 'find_package(jsoncpp REQUIRED)' fails: Unknown CMake command "check_required_components"

[yurivict]

Describe the bug

$ cat CMakeLists.txt 
find_package(jsoncpp REQUIRED)

CMake Error at /usr/local/lib/cmake/jsoncpp/jsoncppConfig.cmake:31 (check_required_components):
  Unknown CMake command "check_required_components".
Call Stack (most recent call first):
  CMakeLists.txt:1 (find_package)

Desktop (please complete the following information):

• OS: FreeBSD 14.1
• cmake-3.29.6
• Meson version: 1.5.1

[kloczek]

It would be good to merge this PR and release new version because issue blocks other projects.

[kloczek]

Tested and with that commit it is OK now.
It would be ASP release new version.

[rpavlik]

So that does not actually fully fix the issue. Sure, it will not error immediately, but it will never set jsoncpp_FOUND to TRUE (or FALSE). That line in CMake calls a macro generated into that file that checks for the presence of the variables and files then sets jsoncpp_FOUND. Without that macro, your Meson-generated config file needs to contain other (presumably manually-written) code to perform this.

The meson-generated file:

####### Expanded from @PACKAGE_INIT@ by configure_package_config_file() #######
####### Any changes to this file will be overwritten by the next CMake run ####
####### The input file was jsoncppConfig.cmake.meson.in ########

get_filename_component(PACKAGE_PREFIX_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../.." ABSOLUTE)

macro(set_and_check _var _file)
  set(${_var} "${_file}")
  if(NOT EXISTS "${_file}")
    message(FATAL_ERROR "File or directory ${_file} referenced by variable ${_var} does not exist !")
  endif()
endmacro()

####################################################################################



add_library(jsoncpp_lib IMPORTED SHARED)
set_target_properties(jsoncpp_lib PROPERTIES
  IMPORTED_LOCATION "${PACKAGE_PREFIX_DIR}/lib/x86_64-linux-gnu/libjsoncpp.so.27"
  INTERFACE_INCLUDE_DIRECTORIES "${PACKAGE_PREFIX_DIR}/include")


include ( "${CMAKE_CURRENT_LIST_DIR}/jsoncpp-namespaced-targets.cmake" )

vs the CMake-generated one:

cmake_policy(PUSH)
cmake_policy(VERSION 3.0...3.26)


####### Expanded from @PACKAGE_INIT@ by configure_package_config_file() #######
####### Any changes to this file will be overwritten by the next CMake run ####
####### The input file was jsoncppConfig.cmake.in                            ########

get_filename_component(PACKAGE_PREFIX_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../" ABSOLUTE)

macro(set_and_check _var _file)
  set(${_var} "${_file}")
  if(NOT EXISTS "${_file}")
    message(FATAL_ERROR "File or directory ${_file} referenced by variable ${_var} does not exist !")
  endif()
endmacro()

macro(check_required_components _NAME)
  foreach(comp ${${_NAME}_FIND_COMPONENTS})
    if(NOT ${_NAME}_${comp}_FOUND)
      if(${_NAME}_FIND_REQUIRED_${comp})
        set(${_NAME}_FOUND FALSE)
      endif()
    endif()
  endforeach()
endmacro()

####################################################################################

include ( "${CMAKE_CURRENT_LIST_DIR}/jsoncpp-targets.cmake" )
include ( "${CMAKE_CURRENT_LIST_DIR}/jsoncpp-namespaced-targets.cmake" )

check_required_components(JsonCpp)

cmake_policy(POP)

(hmm also the capitalization looks inconsistent, I would have to dig through the docs again to figure out whether it actually affects things.)