Ok since I posted the first two attempts I'll add the latest fix here
also (while recognizing that this is a good example of why posting
solutions to email lists is not a good idea in general). The problem
was MAKECMDGOALS which means solution didn't work when switching
between targets. So:
OSMVF = .old_serialized_make_vars
NSMVF = .new_serialized_make_vars
SVDOF = .serialized_vars_diff_output
# Variables To Not Serialize. MAKECMDGOALS is in here because we don't
# consider a change of the target specified on the command line a good
# reason to rebuild everything.
VTNS = MAKECMDGOALS
# Vars To Serialize
VTS = $(filter-out $(VTNS), $(.VARIABLES))
# Put serialization of all VTS flavor/name/value into $(NSMVF)
$(file \
>$(NSMVF), \
$(foreach v,$(VTS),$(flavor $(v)) var $(v) is $(value $(v))$(nl)))
# Create or update $(OSMVF) if necessary
$(shell \
( \
[ -a $(OSMVF) ] \
&& \
(diff $(OSMVF) $(NSMVF) >$(SVDOF)) \
) \
|| \
cp $(NSMVF) $(OSMVF) \
; \
rm $(NSMVF) )
# Build Rule Inputs. This is supposed to list everything that influences
# the build system itself. FIXXME: this won't work right with generated
# dependency files with .mk extensions (so use a different extension :)
BRI = Makefile \
$(wildcard Makefile.*) \
$(shell find . -name "*.mk" -print) \
$(OSMVF)
# Means all targets should depend on target in $(BRI)
.EXTRA_PREREQS = $(BRI)
