From 2e3080feb0a26f6abf4a443f32e51c704ad7e4ea Mon Sep 17 00:00:00 2001
From: Eugene Shalygin <eugene.shalygin@gmail.com>
Date: Mon, 23 Mar 2020 18:04:44 +0100
Subject: [PATCH] Fix PkgConfig generation on Arch

Use first available configuration from the IMPORTED_CONFIGURATIONS list
if no valid property value was found via current or mapped
configurations.

Fixes #4416.
---
 cmake/Modules/GeneratePkgConfig.cmake | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/cmake/Modules/GeneratePkgConfig.cmake b/cmake/Modules/GeneratePkgConfig.cmake
index 0a2f18a56..2099d68e4 100644
--- a/cmake/Modules/GeneratePkgConfig.cmake
+++ b/cmake/Modules/GeneratePkgConfig.cmake
@@ -28,27 +28,39 @@ function(_compile_features_to_gcc_flags _res _features)
 endfunction()
 
 function(_get_target_property_merging_configs _var_name _target_name _propert_name)
-	get_target_property(vals ${_target_name} ${_propert_name})
-	if (NOT vals)
-		set(vals "")
+	get_property(prop_set TARGET ${_target_name} PROPERTY ${_propert_name} SET)
+	if (prop_set)
+		get_property(vals TARGET ${_target_name} PROPERTY ${_propert_name})
+	else()
 		if (CMAKE_BUILD_TYPE)
 			list(APPEND configs ${CMAKE_BUILD_TYPE})
-		elseif()
+		elseif(CMAKE_CONFIGURATION_TYPES)
 			list(APPEND configs ${CMAKE_CONFIGURATION_TYPES})
 		endif()
 		foreach(cfg ${configs})
 			string(TOUPPER "${cfg}" UPPERCFG)
-			get_target_property(mapped_configs ${_target_name} "MAP_IMPORTED_CONFIG_${UPPERCFG}")
+			get_property(mapped_configs TARGET ${_target_name} PROPERTY "MAP_IMPORTED_CONFIG_${UPPERCFG}")
 			if (mapped_configs)
 				list(GET "${mapped_configs}" 0 target_cfg)
 			else()
 				set(target_cfg "${UPPERCFG}")
 			endif()
-			get_target_property(val_for_cfg  ${_target_name} "${_propert_name}_${target_cfg}")
-			if (val_for_cfg)
+			get_property(prop_set TARGET ${_target_name} PROPERTY ${_propert_name}_${target_cfg} SET)
+			if (prop_set)
+				get_property(val_for_cfg TARGET ${_target_name} PROPERTY ${_propert_name}_${target_cfg})
 				list(APPEND vals "$<$<CONFIG:${cfg}>:${val_for_cfg}>")
+				break()
 			endif()
 		endforeach()
+		if (NOT prop_set)
+			get_property(imported_cfgs TARGET ${_target_name} PROPERTY IMPORTED_CONFIGURATIONS)
+			# CMake docs say we can use any of the imported configs
+			list(GET imported_cfgs 0 imported_config)
+			get_property(vals TARGET ${_target_name} PROPERTY ${_propert_name}_${imported_config})
+			# remove config generator expression. Only in this case! Notice we use such expression
+			# ourselves in the loop above
+			string(REPLACE "$<$<CONFIG:${imported_config}>:" "$<1:" vals "${vals}")
+		endif()
 	endif()
 	# HACK for static libraries cmake populates link dependencies as $<LINK_ONLY:lib_name>.
 	# pkg-config does not support special handling for static libraries and as such we will remove