Don't recurse the whole tree looking for a git dir, use PROJECT_SOURCE_DIR

cmake/modules/GetGitRevisionDescription.cmake

@@ -40,26 +40,12 @@ set(__get_git_revision_description YES)
 get_filename_component(_gitdescmoddir ${CMAKE_CURRENT_LIST_FILE} PATH)
 
 function(get_git_head_revision _refspecvar _hashvar)
-	set(GIT_PARENT_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
-	set(GIT_DIR "${GIT_PARENT_DIR}/.git")
-	while(NOT EXISTS "${GIT_DIR}")	# .git dir not found, search parent directories
-		set(GIT_PREVIOUS_PARENT "${GIT_PARENT_DIR}")
-		get_filename_component(GIT_PARENT_DIR ${GIT_PARENT_DIR} PATH)
-		if(GIT_PARENT_DIR STREQUAL GIT_PREVIOUS_PARENT)
-			# We have reached the root directory, we are not in git
-			set(${_refspecvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
-			set(${_hashvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
-			return()
-		endif()
-		set(GIT_DIR "${GIT_PARENT_DIR}/.git")
-	endwhile()
-	# check if this is a submodule
-	if(NOT IS_DIRECTORY ${GIT_DIR})
-		file(READ ${GIT_DIR} submodule)
-		string(REGEX REPLACE "gitdir: (.*)\n$" "\\1" GIT_DIR_RELATIVE ${submodule})
-		get_filename_component(SUBMODULE_DIR ${GIT_DIR} PATH)
-		get_filename_component(GIT_DIR ${SUBMODULE_DIR}/${GIT_DIR_RELATIVE} ABSOLUTE)
-	endif()
+        set(GIT_DIR "${PROJECT_SOURCE_DIR}/.git")
+        if (NOT EXISTS "${GIT_DIR}")	# .git dir not found, search parent directories
+            set(${_hashvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
+            set(${_refspecvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
+            return()
+        endif()
 	set(GIT_DATA "${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/git-data")
 	if(NOT EXISTS "${GIT_DATA}")
 		file(MAKE_DIRECTORY "${GIT_DATA}")