py/mkrules.mk: Use partial clone for submodules if available.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

py/mkrules.mk

@@ -252,7 +252,11 @@ submodules:
 	$(ECHO) "Updating submodules: $(GIT_SUBMODULES)"
 ifneq ($(GIT_SUBMODULES),)
 	$(Q)cd $(TOP) && git submodule sync $(GIT_SUBMODULES)
-	$(Q)cd $(TOP) && git submodule update --init $(GIT_SUBMODULES)
+	# If available, do blobless partial clones of submodules to save time and space.
+	# A blobless partial clone lazily fetches data as needed, but has all the metadata available (tags, etc.).
+	# Fallback to standard submodule update if blobless isn't available (earlier than 2.36.0)
+	$(Q)cd $(TOP) && git submodule update --filter=blob:none --init $(GIT_SUBMODULES) || \
+	  git submodule update --init $(GIT_SUBMODULES)	               
 endif
 .PHONY: submodules