Stepping through macro expansions

Related to https://github.com/rocky/remake/issues/123 ,

I want to debug the following Makefile;
the make-dirs call expands to nothing:

define _make-dir
$1/.dum: $(not-dir $1)/.dum
        mkdir $(dir $@)
        touch $(dir $@)/.dum
endef

# we dont try to create/depend on /.dum
define make-dir
$(if $(not-dir $1),$(call _make-dir,$1),)
endef

$(call make-dir,test/)

I've skimmed through the manual earlier and looked through the in-REPL documentation, maybe I'm missing something but

• I don't see any way to step through macro expansions
• I don't see a way to dump the contents of the file after expansion
• are there other techniques for debugging macros?
  Are there any existing solutions to these, or are there features that could be implemented?

The issue provides a Makefile example and points to related issue #123 and the in-REPL documentation. Start by reviewing those materials and the requested macro-expansion debugging approaches; the payload does not name implementation files or tests, and completion criteria remain to be defined.