Merge "strings.mk: Allow empty RHS values for inputs of collapse-pairs"

endef

###########################################################

## Convert "a=b c= d e = f" into "a=b c=d e=f"

## Convert "a=b c= d e = f = g h=" into "a=b c=d e= f=g h="

##

## $(1): list to collapse

## $(2): if set, separator word; usually "=", ":", or ":="

###########################################################

define collapse-pairs

$(strip \

$(eval _cpSEP := $(strip $(if $(2),$(2),=)))\

$(strip $(subst $(space)$(_cpSEP)$(space),$(_cpSEP),$(strip \

    $(subst $(_cpSEP), $(_cpSEP) ,$(1)))$(space)))

$(eval _cpLHS :=)\

$(eval _cpRET :=)\

$(foreach w,$(subst $(space)$(_cpSEP),$(_cpSEP),$(strip \

            $(subst $(_cpSEP),$(space)$(_cpSEP)$(space),$(1)))),\

  $(if $(findstring $(_cpSEP),$(w)),\

    $(eval _cpRET += $(_cpLHS))$(eval _cpLHS := $(w)),\

    $(eval _cpRET += $(_cpLHS)$(w))$(eval _cpLHS :=)))\

$(if $(_cpLHS),$(_cpRET)$(space)$(_cpLHS),$(_cpRET))\

$(eval _cpSEP :=)\

$(eval _cpLHS :=)\

$(eval _cpRET :=))

endef

# Sanity check for collapse-pairs.

ifneq (a=b c=d e= f=g h=,$(call collapse-pairs,a=b c= d e = f = g h=))

  $(error collapse-pairs sanity check failure)

endif

ifneq (a:=b c:=d e:=f g:=h,$(call collapse-pairs,a:=b c:= d e :=f g := h,:=))

  $(error collapse-pairs sanity check failure)

endif

###########################################################

## Given a list of pairs, if multiple pairs have the same

## first components, keep only the first pair.