Re: solved I think: rebuild if any variable changes. Is it right?

[Britton Kerin]

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)