Double quote bug fix for signature

A while ago I wrote about Shoehorening Keep State into GNU Make. A reader has identified a bug in the code that I presented that causes the code to keep regenerating a target even though the commands have not changed.

This bug occurs if the commands for a target have a double-quote in them. For example, if you have something like:

foo.o:
@compiler -D_DEBUG="YES" foo.c

foo.o will be regenerated every time the Makefile is run. This is because the keep state code echoes the current state of the command to a file and echo strips the double-quotes around YES.

The fix is simple: escape ". Here's the updated code for signature with the fix in it:

include gmsl

last_target :=

dump_var = \$$(eval $1 := $($1))

define new_rule
@echo "$(call map,dump_var,@ % < ? ^ + *)" > $S
@$(if $(wildcard $F),,touch $F)
@echo $@: $F >> $S
endef

define do
$(eval S := $*.sig)$(eval F := $*.force)$(eval C := $(strip $1))
$(if $(call sne,$@,$(last_target)),$(call new_rule),$(eval last_target := $@))
@echo "$(subst ",\",$(subst $$,\$$,$$(if $$(call sne,$(strip $1),$C),$$(shell touch $F))))" >> $S
$C
endef