feat(util): add make functions for listing files

Signed-off-by: Jose Martins <[email protected]>

util.mk

@@ -8,3 +8,43 @@
 define check_variable_defined
 $(if $($(strip $1)),,$(error $(strip $1) not defined: $(strip $2)))
 endef
+
+# Check if a variable is a valid directory path (can be absolute or relative).
+# Returns nothing if false, some unknown value if true.
+# @param directory name
+# @example $(call is_dir, src/core)
+define is_dir
+$(strip $(wildcard $1/.))
+endef
+
+# Check if a variable is a valid file path (not a directory!).
+# Returns nothing if false, some unknown value if true.
+# @param file path (absolute of relative)
+# @example $(call is_dir, src/core/init.c)
+define is_file
+$(if $(strip $(wildcard $1/.)),,$1,)
+endef
+
+# List files within a directory
+# @param directory path (can be absolte of relative)
+# @param a make pattern for the local file name (no relative paths)
+# example $(call list_dir, src, *.c)
+define list_dir_files
+$(strip \
+	$(foreach node, $(wildcard $(strip $1)/$(strip $2)), \
+		$(if $(call is_file, $(node)),$(node))) \
+)
+endef
+
+# List files within a directory and all of its subdirectories
+# @param directory path (can be absolte of relative)
+# @param a make pattern for the local file name (no relative paths)
+# example $(call list_dir_files_recursive, src, *.c)
+define list_dir_files_recursive
+$(strip \
+	$(call list_dir_files, $1, $2) \
+	$(foreach node, $(wildcard $(strip $1)/*), \
+		$(if $(call is_dir, $(node)), 	
+			$(call list_dir_files_recursive, $(node), $(strip $2)))) \
+)
+endef