find_package: Test system package registry when possible

Teach the FindPackagTest to try creating the appropriate HKLM system
package registry value.  If it works then add a test to verify that
find_package() reads it as expected.  Then delete the value to cleanup.

Tests/FindPackageTest/CMakeLists.txt

@@ -37,6 +37,38 @@ FIND_PACKAGE(VersionTestB 1.2)
 FIND_PACKAGE(VersionTestC 1.2.3)
 FIND_PACKAGE(VersionTestD 1.2.3.4)
 
+#-----------------------------------------------------------------------------
+# Test system package registry if possible.
+SET(CMakeTestSystemPackage "")
+IF(WIN32 AND NOT CYGWIN)
+  # Try writing a value to the system package registry.
+  FILE(TO_NATIVE_PATH "${FindPackageTest_SOURCE_DIR}/SystemPackage" _data)
+  SET(_key "HKLM\\Software\\Kitware\\CMake\\Packages\\CMakeTestSystemPackage")
+  SET(_file "${FindPackageTest_BINARY_DIR}/CMakeTestSystemPackage.data")
+  FILE(WRITE ${_file} "${_data}\n")
+  EXECUTE_PROCESS(
+    COMMAND ${CMAKE_COMMAND} -E md5sum ${_file}
+    OUTPUT_VARIABLE _output ERROR_VARIABLE _error RESULT_VARIABLE _failed
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+    )
+  STRING(REGEX REPLACE " .*" "" _value "${_output}")
+  IF(NOT _failed AND _value)
+    EXECUTE_PROCESS(
+      COMMAND reg add "${_key}" /v "${_value}" /t REG_SZ /d "${_data}" /f
+      OUTPUT_VARIABLE _output ERROR_VARIABLE _output RESULT_VARIABLE _failed
+      )
+  ENDIF()
+  # If the above worked, add the rest of the test and a rule to
+  # cleanup the value.
+  IF(NOT _failed)
+    MESSAGE(STATUS "HKLM is writable: enabling CMakeTestSystemPackage")
+    SET(CMakeTestSystemPackage_CLEANUP reg delete "${_key}" /v "${_value}" /f)
+    SET(CMakeTestSystemPackage CMakeTestSystemPackage)
+  ELSE()
+    MESSAGE(STATUS "HKLM is readonly: disabling CMakeTestSystemPackage")
+  ENDIF()
+ENDIF()
+
 #-----------------------------------------------------------------------------
 
 #SET(CMAKE_FIND_DEBUG_MODE 1)
@@ -49,6 +81,7 @@ SET(PACKAGES
   wibbleA wibbleB
   RecursiveA RecursiveB RecursiveC
   EnvA EnvB
+  ${CMakeTestSystemPackage}
   )
 FOREACH(p ${PACKAGES})
   SET(${p}_DIR "" CACHE FILEPATH "Wipe out find results for testing." FORCE)
@@ -116,6 +149,13 @@ SET(ENV{EnvA_DIR} "${CMAKE_CURRENT_SOURCE_DIR}/lib/zot-3.1")
 FIND_PACKAGE(EnvA 3.1 EXACT QUIET NAMES zot) # Should Work
 FIND_PACKAGE(EnvB 3.1 EXACT QUIET NAMES zot) # Should Fail
 
+# Test system package registry if available.
+IF(CMakeTestSystemPackage)
+  FIND_PACKAGE(CMakeTestSystemPackage)
+  EXECUTE_PROCESS(COMMAND ${CMakeTestSystemPackage_CLEANUP}
+    OUTPUT_VARIABLE _output ERROR_VARIABLE _error)
+ENDIF()
+
 # Expected locations at which packages should be found.
 SET(foo_EXPECTED "lib/foo-1.2/foo-config.cmake")
 SET(Foo_EXPECTED "lib/foo-1.2/CMake/FooConfig.cmake")
@@ -145,6 +185,7 @@ SET(RecursiveB_EXPECTED "lib/zot-2.0/zot-config.cmake")
 SET(RecursiveC_EXPECTED "lib/zot-3.1/zot-config.cmake")
 SET(EnvA_EXPECTED "lib/zot-3.1/zot-config.cmake")
 SET(EnvB_MISSING "EnvB_DIR-NOTFOUND")
+SET(CMakeTestSystemPackage_EXPECTED "SystemPackage/CMakeTestSystemPackageConfig.cmake")
 
 # Check the results.
 FOREACH(p ${PACKAGES})

Tests/FindPackageTest/SystemPackage/CMakeTestSystemPackageConfig.cmake

@@ -0,0 +1 @@
+# Test config file.