Nested eval

[David A. Greene]

More fun with GNU make 2.81:

I have this Makefile:

define testa
testa_target := $$(eval $(1))
testa: $$(testa_target)
        touch $$@
        @echo testa done!

TESTS += testa
endef

define testb
$(1):
        touch $$@
        @echo testb done!
endef

testera = $(eval $(call testa,$(1)))
testerb = $(eval $(call testb,$(1))) $(1)

__sink := $(call testera,$$(call testerb,targetb))

all: $(TESTS)

The intent is to generate rule testa to depend on the target of the rule 
created by invoking testerb.

A "make all" results in this:

test.mk:19: *** missing separator.  Stop.

A "remake all" (GNU make debugger) gives this:

Reading makefiles...
Reading makefile `test.mk'...
calling testera("$(call testerb,targetb)")
 calling testa("$(call testerb,targetb)")
 testa() returns "testa_target := $(eval $(call testerb,targetb))
testa: $(testa_target)
        touch $@
        @echo testa done!

TESTS += testa"
 calling testerb("targetb")
  calling testb("targetb")
  testb() returns "targetb:
        touch $@
        @echo testb done!"
 testerb() returns " targetb"
test.mk:19: *** missing separator.  Stop.
Command-line arguments:
        "-d -f test.mk"

So it looks like things are generated correctly but remake never reports
the return value for the call to testera, almost like the call sequence got
prematurely terminated.

Is doing a nested eval like this legal?  If not, is there an alternative way
to do what I'm attempting?

                                        -Dave