Fetch dependencies recursively

This uses some general make tools, most notably "while" and "select" which come from
https://github.com/markpiffer/gmtt.git and which allow us to recursively parse the
.dep files in the given e3 installation. Broadly speaking, we start with all variables
of the form `%_DEP_VERSION` to determine the first line of dependent modules, and then
we ask them (using `fetch_deps`) what they depend on.

require-ess/tools/driver.makefile

@@ -423,6 +423,46 @@ ifeq ($(filter O.%,$(notdir ${CURDIR})),)
 ## RUN 3
 # Target architecture defined.
 # Still in source directory, third run.
+
+# First, sort out all of the dependencies. This is done recursively using tools from https://github.com/markpiffer/gmtt.git
+
+space := $(strip) $(strip)#
+comma := ,#
+list2param = $(subst $(space),$(comma),$(strip $1))
+exec = $(eval -exec=$1)$(eval -exec:=$$(call -exec,$(call list2param,$2)))$(-exec)
+while = $(if $(call exec,$1),$(eval $2)$(call while,$1,$2,$3),$(eval $3))
+
+pick = $(foreach elem,$1,$(word $(elem),$2))
+
+select = $(strip $(call -select,$1,$(strip $2),$3))
+-select = $(call --select,$(wordlist 2,2147483647,$2),$(firstword $2),3,$1,$3)
+--select = $(if $1,$(if $(call exec,$5,$(call list2param,$(wordlist 1,$2,$1))), $(call pick,$4,$1))$(call --select,$(wordlist $3,2147483647,$1),$2,$3,$4,$5))
+
+str-eq = $(if $(subst x$1,,x$2),,t)
+
+define fetch_deps
+2 $(shell cat $(E3_SITEMODS_PATH)/$1/$($1_VERSION)/lib/$(T_A)/$1.dep | sed '1d')
+endef
+
+define update_dep_versions
+m := $$(firstword $$(_MODULES))
+REQUIRED += $$m
+$$m_TBL := $$(call fetch_deps,$$m)
+$$m_DEPS := $$(call select,1,$$($$m_TBL),1)
+_MODULES := $$(filter-out $$(REQUIRED),$$(_MODULES) $$($$m_DEPS))
+$$(foreach mm,$$($$m_DEPS),$$(eval export $$(mm)_VERSION := $$(call select,2,$$($$m_TBL),$$$$(call str-eq,$$$$1,$$(mm)))))
+endef
+
+# Convert (for example) ASYN_DEP_VERSION to asyn_VERSION and add asyn to the list of modules
+_MODULES :=
+REQUIRED :=
+$(foreach m,$(patsubst %_DEP_VERSION,%,$(filter %_DEP_VERSION,$(.VARIABLES))),\
+$(eval _lm := $(shell echo $m | tr '[:upper:]' '[:lower:]'))\
+$(eval export $(_lm)_VERSION := $($m_DEP_VERSION))\
+$(eval _MODULES += $(_lm)))
+
+$(call while,$$(_MODULES),$(update_dep_versions))
+
 debug::
 	@echo "===================== Pass 3: T_A = $(T_A) ====================="
 	@echo "BINS = $(BINS)"