commit 4740a8cc6a0119abdc735cf0c3f536999bfeebd9
Author: Sam Thursfield <sam.thursfield@codethink.co.uk>
Date:   Tue Oct 20 22:40:42 2015 +0200

    FindPkgConfig: Honour search path in pkg_get_variable
    
    The pkg_get_variable did not take into account the search path set by
    CMAKE_PREFIX_PATH, which meant that it would not work for packages
    installed in a non-standard location.
    
    It now uses the same code path as pkg_check_modules() to set up the
    PKG_CONFIG_PATH search path before running `pkg-config`.

diff --git a/Modules/FindPkgConfig.cmake b/Modules/FindPkgConfig.cmake
index e822b9c..e958deb 100644
--- a/Modules/FindPkgConfig.cmake
+++ b/Modules/FindPkgConfig.cmake
@@ -105,7 +105,13 @@ endmacro()
     pkg_get_variable(GI_GIRDIR gobject-introspection-1.0 girdir)
 #]========================================]
 function (pkg_get_variable result pkg variable)
+  set(_pkgconfig_path_old $ENV{PKG_CONFIG_PATH})
+
+  _pkg_set_cmake_pkgconfig_path(0 0)
   _pkgconfig_invoke("${pkg}" "prefix" "result" "" "--variable=${variable}")
+
+  set(ENV{PKG_CONFIG_PATH} ${_pkgconfig_path_old})
+
   set("${result}"
     "${prefix_result}"
     PARENT_SCOPE)
@@ -182,6 +188,73 @@ function(_pkgconfig_add_extra_path _extra_paths_var _var)
 endfunction()
 
 ###
+function(_pkg_set_cmake_pkgconfig_path _no_cmake_path _no_cmake_environment_path)
+  if(NOT _no_cmake_path)
+    _pkgconfig_add_extra_path(_extra_paths CMAKE_PREFIX_PATH)
+    _pkgconfig_add_extra_path(_extra_paths CMAKE_FRAMEWORK_PATH)
+    _pkgconfig_add_extra_path(_extra_paths CMAKE_APPBUNDLE_PATH)
+  endif()
+
+  if(NOT _no_cmake_environment_path)
+    _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_PREFIX_PATH)
+    _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_FRAMEWORK_PATH)
+    _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_APPBUNDLE_PATH)
+  endif()
+
+  if(NOT "${_extra_paths}" STREQUAL "")
+    # Add paths from the CMAKE_PREFIX_PATH variables. It's up to the caller to
+    # save the original value of the PKG_CONFIG_PATH environment variable.
+    set(_pkgconfig_path ENV{PKG_CONFIG_PATH})
+    if(NOT "${_pkgconfig_path}" STREQUAL "")
+      file(TO_CMAKE_PATH "${_pkgconfig_path}" _pkgconfig_path)
+    endif()
+
+    # Create a list of the possible pkgconfig subfolder (depending on
+    # the system
+    set(_lib_dirs)
+    if(NOT DEFINED CMAKE_SYSTEM_NAME
+        OR (CMAKE_SYSTEM_NAME MATCHES "^(Linux|kFreeBSD|GNU)$"
+            AND NOT CMAKE_CROSSCOMPILING))
+      if(EXISTS "/etc/debian_version") # is this a debian system ?
+        if(CMAKE_LIBRARY_ARCHITECTURE)
+          list(APPEND _lib_dirs "lib/${CMAKE_LIBRARY_ARCHITECTURE}/pkgconfig")
+        endif()
+      else()
+        # not debian, chech the FIND_LIBRARY_USE_LIB64_PATHS property
+        get_property(uselib64 GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS)
+        if(uselib64)
+          list(APPEND _lib_dirs "lib64/pkgconfig")
+        endif()
+      endif()
+    endif()
+    list(APPEND _lib_dirs "lib/pkgconfig")
+
+    # Check if directories exist and eventually append them to the
+    # pkgconfig path list
+    foreach(_prefix_dir ${_extra_paths})
+      foreach(_lib_dir ${_lib_dirs})
+        if(EXISTS "${_prefix_dir}/${_lib_dir}")
+          list(APPEND _pkgconfig_path "${_prefix_dir}/${_lib_dir}")
+          list(REMOVE_DUPLICATES _pkgconfig_path)
+        endif()
+      endforeach()
+    endforeach()
+
+    # Prepare and set the environment variable
+    if(NOT "${_pkgconfig_path}" STREQUAL "")
+      # remove empty values from the list
+      list(REMOVE_ITEM _pkgconfig_path "")
+      file(TO_NATIVE_PATH "${_pkgconfig_path}" _pkgconfig_path)
+      if(UNIX)
+        string(REPLACE ";" ":" _pkgconfig_path "${_pkgconfig_path}")
+        string(REPLACE "\\ " " " _pkgconfig_path "${_pkgconfig_path}")
+      endif()
+      set(ENV{PKG_CONFIG_PATH} ${_pkgconfig_path})
+    endif()
+  endif()
+endfunction()
+
+###
 macro(_pkg_check_modules_internal _is_required _is_silent _no_cmake_path _no_cmake_environment_path _prefix)
   _pkgconfig_unset(${_prefix}_FOUND)
   _pkgconfig_unset(${_prefix}_VERSION)
@@ -221,76 +294,8 @@ macro(_pkg_check_modules_internal _is_required _is_silent _no_cmake_path _no_cma
     set(_pkg_check_modules_packages)
     set(_pkg_check_modules_failed)
 
-    set(_extra_paths)
-
-    if(NOT _no_cmake_path)
-      _pkgconfig_add_extra_path(_extra_paths CMAKE_PREFIX_PATH)
-      _pkgconfig_add_extra_path(_extra_paths CMAKE_FRAMEWORK_PATH)
-      _pkgconfig_add_extra_path(_extra_paths CMAKE_APPBUNDLE_PATH)
-    endif()
-
-    if(NOT _no_cmake_environment_path)
-      _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_PREFIX_PATH)
-      _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_FRAMEWORK_PATH)
-      _pkgconfig_add_extra_path(_extra_paths ENV CMAKE_APPBUNDLE_PATH)
-    endif()
-
-    if(NOT "${_extra_paths}" STREQUAL "")
-      # Save the PKG_CONFIG_PATH environment variable, and add paths
-      # from the CMAKE_PREFIX_PATH variables
-      set(_pkgconfig_path_old $ENV{PKG_CONFIG_PATH})
-      set(_pkgconfig_path ${_pkgconfig_path_old})
-      if(NOT "${_pkgconfig_path}" STREQUAL "")
-        file(TO_CMAKE_PATH "${_pkgconfig_path}" _pkgconfig_path)
-      endif()
-
-      # Create a list of the possible pkgconfig subfolder (depending on
-      # the system
-      set(_lib_dirs)
-      if(NOT DEFINED CMAKE_SYSTEM_NAME
-          OR (CMAKE_SYSTEM_NAME MATCHES "^(Linux|kFreeBSD|GNU)$"
-              AND NOT CMAKE_CROSSCOMPILING))
-        if(EXISTS "/etc/debian_version") # is this a debian system ?
-          if(CMAKE_LIBRARY_ARCHITECTURE)
-            list(APPEND _lib_dirs "lib/${CMAKE_LIBRARY_ARCHITECTURE}/pkgconfig")
-          endif()
-        else()
-          # not debian, chech the FIND_LIBRARY_USE_LIB64_PATHS property
-          get_property(uselib64 GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS)
-          if(uselib64)
-            list(APPEND _lib_dirs "lib64/pkgconfig")
-          endif()
-        endif()
-      endif()
-      list(APPEND _lib_dirs "lib/pkgconfig")
-
-      # Check if directories exist and eventually append them to the
-      # pkgconfig path list
-      foreach(_prefix_dir ${_extra_paths})
-        foreach(_lib_dir ${_lib_dirs})
-          if(EXISTS "${_prefix_dir}/${_lib_dir}")
-            list(APPEND _pkgconfig_path "${_prefix_dir}/${_lib_dir}")
-            list(REMOVE_DUPLICATES _pkgconfig_path)
-          endif()
-        endforeach()
-      endforeach()
-
-      # Prepare and set the environment variable
-      if(NOT "${_pkgconfig_path}" STREQUAL "")
-        # remove empty values from the list
-        list(REMOVE_ITEM _pkgconfig_path "")
-        file(TO_NATIVE_PATH "${_pkgconfig_path}" _pkgconfig_path)
-        if(UNIX)
-          string(REPLACE ";" ":" _pkgconfig_path "${_pkgconfig_path}")
-          string(REPLACE "\\ " " " _pkgconfig_path "${_pkgconfig_path}")
-        endif()
-        set(ENV{PKG_CONFIG_PATH} ${_pkgconfig_path})
-      endif()
-
-      # Unset variables
-      unset(_lib_dirs)
-      unset(_pkgconfig_path)
-    endif()
+    set(_pkgconfig_path_old ENV{PKG_CONFIG_PATH})
+    _pkg_set_cmake_pkgconfig_path(${_no_cmake_path} ${_no_cmake_environment_path})
 
     # iterate through module list and check whether they exist and match the required version
     foreach (_pkg_check_modules_pkg ${_pkg_check_modules_list})
@@ -396,12 +401,9 @@ macro(_pkg_check_modules_internal _is_required _is_silent _no_cmake_path _no_cma
       _pkgconfig_invoke_dyn("${_pkg_check_modules_packages}" "${_prefix}" CFLAGS_OTHER        ""        --cflags-only-other )
     endif()
 
-    if(NOT "${_extra_paths}" STREQUAL "")
-      # Restore the environment variable
-      set(ENV{PKG_CONFIG_PATH} ${_pkgconfig_path})
-    endif()
+    # Restore the environment variable
+    set(ENV{PKG_CONFIG_PATH} ${_pkgconfig_path_old})
 
-    unset(_extra_paths)
     unset(_pkgconfig_path_old)
   else()
     if (${_is_required})