File fix-cmake-export.patch of Package yaml-cpp

From c1f987850a6282435f499bee76b12e32d7472f12 Mon Sep 17 00:00:00 2001
From: Felix <flx107809@gmail.com>
Date: Thu, 30 Dec 2021 15:35:54 +0100
Subject: [PATCH] fix cmake export

After configure the file `yaml-cpp-config.cmake.in` the result ends up with
empty variables.  (see also the discussion in #774).

Rework this file and the call to `configure_package_config_file` according the
cmake documentation
(https://cmake.org/cmake/help/v3.22/module/CMakePackageConfigHelpers.html?highlight=configure_package_config#command:configure_package_config_file)
to overcome this issue and allow a simple `find_package` after install.

As there was some discussion about the place where to install the
`yaml-cpp-config.cmake` file, e.g. #1055, factor out the install location into
an extra variable to make it easier changing this location in the future.
---
 CMakeLists.txt           | 17 ++++++++++++-----
 yaml-cpp-config.cmake.in | 10 ++++++----
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6adbf45a2..e9310792e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -129,10 +129,16 @@ set_target_properties(yaml-cpp PROPERTIES
   PROJECT_LABEL "yaml-cpp ${yaml-cpp-label-postfix}"
   DEBUG_POSTFIX "${CMAKE_DEBUG_POSTFIX}")
 
+# FIXME(felix2012): A more common place for the cmake export would be
+# `CMAKE_INSTALL_LIBDIR`, as e.g. done in ubuntu or in this project for GTest
+set(CONFIG_EXPORT_DIR "${CMAKE_INSTALL_DATADIR}/cmake/yaml-cpp")
+set(EXPORT_TARGETS yaml-cpp)
 configure_package_config_file(
   "${PROJECT_SOURCE_DIR}/yaml-cpp-config.cmake.in"
   "${PROJECT_BINARY_DIR}/yaml-cpp-config.cmake"
-  INSTALL_DESTINATION "${CMAKE_INSTALL_DATADIR}/cmake/yaml-cpp")
+  INSTALL_DESTINATION "${CONFIG_EXPORT_DIR}"
+  PATH_VARS CMAKE_INSTALL_INCLUDEDIR CONFIG_EXPORT_DIR)
+unset(EXPORT_TARGETS)
 
 write_basic_package_version_file(
   "${PROJECT_BINARY_DIR}/yaml-cpp-config-version.cmake"
@@ -150,14 +156,15 @@ if (YAML_CPP_INSTALL)
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
                 FILES_MATCHING PATTERN "*.h")
   install(EXPORT yaml-cpp-targets
-    DESTINATION "${CMAKE_INSTALL_DATADIR}/cmake/yaml-cpp")
+    DESTINATION "${CONFIG_EXPORT_DIR}")
   install(FILES
-                "${PROJECT_BINARY_DIR}/yaml-cpp-config.cmake"
-                "${PROJECT_BINARY_DIR}/yaml-cpp-config-version.cmake"
-    DESTINATION "${CMAKE_INSTALL_DATADIR}/cmake/yaml-cpp")
+      "${PROJECT_BINARY_DIR}/yaml-cpp-config.cmake"
+      "${PROJECT_BINARY_DIR}/yaml-cpp-config-version.cmake"
+    DESTINATION "${CONFIG_EXPORT_DIR}")
   install(FILES "${PROJECT_BINARY_DIR}/yaml-cpp.pc"
     DESTINATION ${CMAKE_INSTALL_DATADIR}/pkgconfig)
 endif()
+unset(CONFIG_EXPORT_DIR)
 
 if(YAML_CPP_BUILD_TESTS)
   add_subdirectory(test)
diff --git a/yaml-cpp-config.cmake.in b/yaml-cpp-config.cmake.in
index 7b41e3f30..a7ace3dc0 100644
--- a/yaml-cpp-config.cmake.in
+++ b/yaml-cpp-config.cmake.in
@@ -3,12 +3,14 @@
 #  YAML_CPP_INCLUDE_DIR - include directory
 #  YAML_CPP_LIBRARIES    - libraries to link against
 
-# Compute paths
-get_filename_component(YAML_CPP_CMAKE_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
-set(YAML_CPP_INCLUDE_DIR "@CONFIG_INCLUDE_DIRS@")
+@PACKAGE_INIT@
+
+set_and_check(YAML_CPP_INCLUDE_DIR "@PACKAGE_CMAKE_INSTALL_INCLUDEDIR@")
 
 # Our library dependencies (contains definitions for IMPORTED targets)
-include("${YAML_CPP_CMAKE_DIR}/yaml-cpp-targets.cmake")
+include(@PACKAGE_CONFIG_EXPORT_DIR@/yaml-cpp-targets.cmake)
 
 # These are IMPORTED targets created by yaml-cpp-targets.cmake
 set(YAML_CPP_LIBRARIES "@EXPORT_TARGETS@")
+
+check_required_components(@EXPORT_TARGETS@)