luci.mk: add simple cache buster

Append a ?v=version string to any media or resource URL that has a .js or .css
extension.

Also substitute placeholders in the form <%# xxxPKG_VERSION %> where
xxx is replaced verbatim and PKG_VERSION with the actual version, e.g.
<%# ?x=PKG_VERSION %> will result in "?x=git-16.237.30043-f885853".

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

luci.mk

@@ -155,12 +155,21 @@ define SrcDiet
 	done
 endef
 
+define SubstituteVersion
+	$(FIND) $(1) -type f -name '*.htm' | while read src; do \
+		$(SED) 's/<%# *\([^ ]*\)PKG_VERSION *%>/\1$(PKG_VERSION)/g' \
+		    -e 's/"\(<%= *\(media\|resource\) *%>[^"]*\.\(js\|css\)\)"/"\1?v=$(PKG_VERSION)"/g' \
+			"$$$$src"; \
+	done
+endef
+
 define Package/$(PKG_NAME)/install
 	if [ -d $(PKG_BUILD_DIR)/luasrc ]; then \
 	  $(INSTALL_DIR) $(1)$(LUCI_LIBRARYDIR); \
 	  cp -pR $(PKG_BUILD_DIR)/luasrc/* $(1)$(LUCI_LIBRARYDIR)/; \
 	  $(FIND) $(1)$(LUCI_LIBRARYDIR)/ -type f -name '*.luadoc' | $(XARGS) rm; \
 	  $(if $(CONFIG_LUCI_SRCDIET),$(call SrcDiet,$(1)$(LUCI_LIBRARYDIR)/),true); \
+	  $(call SubstituteVersion,$(1)$(LUCI_LIBRARYDIR)/); \
 	else true; fi
 	if [ -d $(PKG_BUILD_DIR)/htdocs ]; then \
 	  $(INSTALL_DIR) $(1)$(HTDOCS); \