Improve initialize macro.

.gitmodules

@@ -1,6 +1,6 @@
-[submodule "vendor/googletest"]
+[submodule "googletest"]
 	path = vendor/googletest
 	url = https://github.com/google/googletest.git
-[submodule "vendor/fmt"]
+[submodule "fmt"]
 	path = vendor/fmt
 	url = https://github.com/fmtlib/fmt.git

cmake/initialize-submodules.cmake

@@ -1,36 +1,89 @@
 #update the named submodule
-macro(update_submodule module_name module_path)
-  if(NOT EXISTS "${module_path}")
-    message(FATAL_ERROR "Submodule directory \"${module_path}\" does not exist")
-  endif()
-
-  # Initialize submodule if it hasn't already been cloned
-  if(NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/${module_name}/.git")
-    message(STATUS "Initialize ${module_name} submodule")
-    execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init "${module_path}"
-            WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
-            RESULT_VARIABLE GIT_SUBMOD_RESULT)
-    if(NOT GIT_SUBMOD_RESULT EQUAL "0")
-      message(FATAL_ERROR "git submodule update --init ${module_path} failed with ${GIT_SUBMOD_RESULT}, please checkout submodules")
-    endif()
-  endif()
-endmacro()
 
-#update the named submodule iff it is listed in .gitmodules
+#attempt to add the submodule
+#optional arguments:
+# 1 - path
+# 2 - alternate reference name
 macro(add_submodule module_name)
 
+  message(STATUS "Attempting to add \"${module_name}\"")
   #check of specific path is provided
   set(MacroArgs ${ARGN})
   list(LENGTH MacroArgs NumArgs)
+
+  set(have_submodule FALSE)
+  set(have_path FALSE)
+
+  # first optional argument is module path
   if(NumArgs GREATER 0)
     set(module_path ${ARGV1})
   else()
     set(module_path ${CMAKE_CURRENT_SOURCE_DIR}/${module_name})
   endif()
-  message(${module_path})
 
-  if (NOT TARGET ${module_name})
-    update_submodule(${module_name} ${module_path})
-    add_subdirectory(${module_path})
+  # second optional argument is module reference
+  if(NumArgs GREATER 1)
+    set(module_ref_name ${ARGV2})
+  else()
+    set(module_ref_name ${module_name})
   endif()
+
+  set(is_submodule FALSE)
+  if(GIT_FOUND AND EXISTS "${PROJECT_SOURCE_DIR}/.git")
+    set(git_modules_file "${PROJECT_SOURCE_DIR}/.gitmodules")
+    if (EXISTS ${git_modules_file})
+      file(STRINGS ${git_modules_file} file_lines)
+      set(have_path FALSE)
+
+      foreach(line ${file_lines})
+        if (NOT is_submodule)
+          string(COMPARE EQUAL ${line} "[submodule \"${module_ref_name}\"]" is_submodule)
+          if (is_submodule)
+            message(STATUS "\"${module_name}\" is a submodule of this project.")
+            continue()
+          endif()
+        endif()
+
+        if (is_submodule AND (NOT have_path))
+          string(FIND ${line} "path =" pos)
+          set(have_path NOT(pos EQUALS -1))
+          if (have_path)
+            string(REPLACE "path =" "" submodule_path ${line})
+            string(STRIP "${submodule_path}" submodule_path)
+            set(submodule_path "${PROJECT_SOURCE_DIR}/${submodule_path}")
+            continue()
+          endif()
+        endif()
+      endforeach()
+
+      if(is_submodule)
+        if(have_path)
+          message(STATUS "Updating submodule \"${module_name}\" at ${submodule_path}")
+          execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive "${submodule_path}"
+                  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+                  RESULT_VARIABLE GIT_SUBMOD_RESULT)
+          if(GIT_SUBMOD_RESULT EQUAL "0")
+            message(STATUS "Successfully updated submodule \"${module_name}\"")
+          else()
+            message(FATAL_ERROR "Unable to update submodule \"${module_name}\"")
+          endif()
+        endif()
+      else()
+        message(STATUS "\"${module_name}\" is not a submodule of this project")
+      endif()
+
+    endif()
+  endif()
+
+  if (TARGET ${module_name})
+    message(STATUS "Submodule \"${module_name}\" is a target.")
+  else()
+    if(EXISTS "${module_path}")
+      message(STATUS "Adding subdirectory ${module_path} to this project")
+      add_subdirectory(${module_path})
+    endif()
+  endif()
+
+  message("")
+
 endmacro()