Add list-keymaps make target (qmk#5563)

Makefile

@@ -371,6 +371,9 @@ define PARSE_KEYBOARD
  # The same if all was specified
  else ifeq ($$(call COMPARE_AND_REMOVE_FROM_RULE,all),true)
  $$(eval $$(call PARSE_ALL_KEYMAPS))
+ # List all keymaps for the given keyboard
+ else ifeq ($$(call COMPARE_AND_REMOVE_FROM_RULE,list-keymaps),true)
+ $$(eval $$(call LIST_ALL_KEYMAPS))
  # Try to match the specified keyamp with the list of known keymaps
  else ifeq ($$(call TRY_TO_MATCH_RULE_FROM_LIST,$$(KEYMAPS)),true)
  $$(eval $$(call PARSE_KEYMAP,$$(MATCHED_ITEM)))
@@ -407,6 +410,16 @@ endef
 # endif
 # endef
 
+# Prints a list of all known keymaps for the given keyboard
+define LIST_ALL_KEYMAPS
+ COMMAND_true_LIST_KEYMAPS := \
+ printf "$$(KEYMAPS)\n";
+ COMMAND_false_LIST_KEYMAPS := \
+ printf "$$(MSG_AVAILABLE_KEYMAPS)\n"; \
+ printf "$$(KEYMAPS)\n";
+ COMMANDS += LIST_KEYMAPS
+endef
+
 # $1 Keymap
 # This is the meat of compiling a keyboard, when entering this, everything is known
 # keyboard, subproject, and keymap

message.mk

@@ -76,6 +76,11 @@ define GENERATE_MSG_MAKE_TEST
 endef
 MSG_MAKE_TEST = $(eval $(call GENERATE_MSG_MAKE_TEST))$(MSG_MAKE_TEST_ACTUAL)
 MSG_TEST = Testing $(BOLD)$(TEST_NAME)$(NO_COLOR)
+define GENERATE_MSG_AVAILABLE_KEYMAPS
+ MSG_AVAILABLE_KEYMAPS_ACTUAL := Available keymaps for $(BOLD)$$(CURRENT_KB)$(NO_COLOR):
+endef
+MSG_AVAILABLE_KEYMAPS = $(eval $(call GENERATE_MSG_AVAILABLE_KEYMAPS))$(MSG_AVAILABLE_KEYMAPS_ACTUAL)
+
 MSG_CHECK_FILESIZE = Checking file size of $(TARGET).hex
 MSG_FILE_TOO_BIG = $(ERROR_COLOR)The firmware is too large!$(NO_COLOR) $(CURRENT_SIZE)/$(MAX_SIZE) ($(OVER_SIZE) bytes over)\n
 MSG_FILE_TOO_SMALL = The firmware is too small! $(CURRENT_SIZE)/$(MAX_SIZE)\n