push git related logic to cmake, now that i know how to do that kind of thing

cmake/Modules/Git.cmake

@@ -0,0 +1,52 @@
+function(git_init)
+    set(options "")
+    set(oneValueArgs SUBMODULE_DIR)
+    set(multiValueArgs "")
+    cmake_parse_arguments(GIT_INIT "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
+
+    set(GIT_SUBMODULE_DIR "${GIT_INIT_SUBMODULE_DIR}" PARENT_SCOPE)
+    set(GIT_SUBMODULE_DIR_ABS "${CMAKE_SOURCE_DIR}/${GIT_INIT_SUBMODULE_DIR}" PARENT_SCOPE)
+
+    execute_process(COMMAND git rev-parse --git-dir
+        WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
+        OUTPUT_QUIET
+        RESULT_VARIABLE GIT_REPO_RESULT)
+
+    if ("${GIT_REPO_RESULT}" STREQUAL "0")
+        set(IS_GIT_REPO TRUE)
+        set(IS_GIT_REPO TRUE PARENT_SCOPE)
+    else("${GIT_REPO_RESULT}" STREQUAL "0")
+        set(IS_GIT_REPO FALSE)
+        set(IS_GIT_REPO FALSE PARENT_SCOPE)
+    endif("${GIT_REPO_RESULT}" STREQUAL "0")
+
+    if(IS_GIT_REPO)
+        execute_process(COMMAND git log --pretty=format:%H -n 1
+            OUTPUT_VARIABLE GIT_COMMIT_HASH)
+        string(STRIP "${GIT_COMMIT_HASH}" GIT_COMMIT_HASH)
+        set(GIT_COMMIT_HASH ${GIT_COMMIT_HASH} PARENT_SCOPE)
+        
+        execute_process(COMMAND git symbolic-ref HEAD
+            COMMAND cut -d/ -f3
+            OUTPUT_VARIABLE GIT_BRANCH)
+        string(STRIP "${GIT_BRANCH}" GIT_BRANCH)
+        set(GIT_BRANCH ${GIT_BRANCH} PARENT_SCOPE)
+
+        message(STATUS "commit ${GIT_COMMIT_HASH}, branch ${GIT_BRANCH}")
+    else(IS_GIT_REPO)
+        message(STATUS "This is not a git repo, assuming this tarball actually packaged everything...")
+    endif(IS_GIT_REPO)
+endfunction(git_init)
+
+function(git_submodule)
+    if(IS_GIT_REPO)
+        set(oneValueArgs TARGET REMOTE_URL)
+        set(multiValueArgs "")
+        cmake_parse_arguments(GIT_SUBMODULE "" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
+
+        execute_process(COMMAND git submodule update --init -- "${GIT_SUBMODULE_DIR}/${GIT_SUBMODULE_TARGET}"
+            WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
+            COMMENT "Updating submodule ${GIT_SUBMODULE_DIR}/${GIT_SUBMODULE_TARGET}"
+            VERBATIM)
+    endif(IS_GIT_REPO)
+endfunction(git_submodule)