probe.mak

# Testbed for examining Make's behavior

#
# var: Show value of $(var) in a this instance and an empty makefile.
#
#  * `make var var=MAKEFLAGS -j2`:  MAKEFLAGS differs between
#    reading and rule processing phases.
#
#  * MAKEFLAGS & MFLAGS: Parsing MAKEFLAGS to detect `-r`, etc, is
#    non-trivial, whereas $(findstring r,$(word 1,MFLAGS)) appears to work.
#
var ?= .VARIABLES
subflags = -R
emptyget = $(shell make $1 -f - <<<'$$(info $$($(var)))_x:;@true')

var1 := $($(var))

var: ; @true\
  $(info phase1  : $(var) = $(var1))\
  $(info phase2  : $(var) = $($(var)))\
  $(info empty   : $(var) = $(call emptyget,$(subflags)))


#
# subdiff: Diff $(var) between this instance and `make $(subflags)`
#
diff = $(info -: $(sort $(filter-out $2,$1)))\
       $(info +: $(sort $(filter-out $1,$2)))

subdiff: ; @true\
  $(info This instance --> `make $(subflags)`:)\
  $(info $(call diff,$($(var)),$(call emptyget,$(subflags))))


#
# Diff $(var) between two submakes, one with $(subflags).
#
flagdiff: ; @true\
  $(info `make` --> `make $(subflags)`)\
  $(info $(call diff,$(emptyget),$(call emptyget,$(subflags))))


#
# Demonstrate parallelization
#
#   * `make par` takes 5 seconds
#   * `make par -j5` takes 1 second.
#   * `make par setflags=-j5` takes 1 second => setting MAKEFLAGS=-jN
#     affects the current Make instance.
#

ifdef setflags
  $(info MAKEFLAGS := $(setflags))
  MAKEFLAGS := $(setflags)
endif

par: 1.sleep 2.sleep 3.sleep 4.sleep 5.sleep

%.sleep: ; @echo $* start && sleep 1 && echo $* end


#
# Invoke self as sub-make
#
#  * `make submake setflags=-j5` warns "disabling jobserver".
#    Setting MAKEFLAGS=-jN creates this problem with submakes.
#

submake ?= par

submake: ; @$(MAKE) -f $(word 1,$(MAKEFILE_LIST)) $(submake)


#
# Expansion of recipes
#
#  * When recipes are expanded at build time, they can contain
#    newlines without tabs, even when in a one-line rule context.
#

define lazyRecipe
# comment
echo foo
@echo bar
echo baz
endef

lazy-test:
	$(lazyRecipe)

lazy2-test: ; $(lazyRecipe)


#
# Odd variable names
#
#  * We can define and use @ prior to rule processing phase, but during rule
#    processing phase it will use Make's automatic definition.
#
#  * $(VAR) is a problem when VAR contains ":" ... even if it is expanded
#    from a var or function call.
#
#  * $(call VAR) is a problem when VAR contains ":" or ")" ... even if those
#    are expanded from vars!
#
#  * Make 3.81
#       a<b = A<B
#       a>b = A<B
#       a$(EQ)n = A=B (if)
#       a$Cn = A:B (if)
#       a$(if ,,:)b = A:B (if)
#       a$Hb = A#B (if)
#       a$(if ,,\#)b =
#       @ = var-test now; but was MYDEF before rule processing.
#

E = =
C = :
H = \#
L = (
R = )
P = %

a = !A!
b = !B!
a b = A B
a<b = A<B
a>b = A<B
a$(if ,,=)b = A=B
a$(if ,,:)b = A:B
a$(if ,,\#)b = A\#B
a)b = A)B
a(b)c = A(B)C
a$(if ,,:%=%)b = A:%=%B


@ = MYDEF

PRE@ := $@
ifneq "$@" "MYDEF"
  $(error Cannot override "@" prior in expansion phase)
endif

var-test:
	@echo '$$(a b)             = $(a b)'
	@echo '$$(a>b)             = $(a>b)'
	@echo '$$(a$$En)            = $(a$Eb)'
	@echo '$$(a#b)             = $(a#b)'
	@echo '$$(a:b)             = $(a:b)'
	@echo '$$(a$$(if ,,:)%=%b)  = $(a$(if ,,:%=)%b)       ***'
	@echo '$$(call a:%=%b)     = $(call a:%=%b)       ***'
	@echo '$$(call a$$C$$P$$E$$Pb) = $(call a$C$P$E$Pb)       ***'
	@echo '$$(value a:%=%b)    = $(value a:%=%b)'
	@echo '$$(a)b)             = $(a$Rb)'
	@echo '$$(call a)b)        = $(call a$Rb)      ***'
	@echo '$$(call a(b)c)      = $(call a(b)c)         ***'
	@echo '$$(@) = $@ now; but was $(PRE@) before rule processing.'


#
# Escaping characters in targets
#
# Make 3.81:
#   * `a\ b` escapes "a b", as target or prereq.
#   * `a*b` globs as prereq (and as target!).  "Glob" means if there no file
#      matching the wildcard expression, then the wildcard expression
#      remains unchanges.
#   * `a\*b` does NOT escape the "*" (the "\" remains).
#   * `a\:b` escapes "a:b" in target; NOT in prereq.
#   * `a\=b` escapes "a=b" in prereq; NOT in target.
#


.PHONY: minion.md

m*d: ; @echo 'A: $$@ = "$@"'
a*b: ; @echo 'B: $$@ = "$@"'
m\*d: ; @echo 'C: $$@ = "$@"'
a\ b: ; @echo 'D: $$@ = "$@"'
a\:b: ; @echo 'E: $$@ = "$@"'
a\\\:b: ; @echo 'F: $$@ = "$@"'
a\b: ; @echo 'G: $$@ = "$@"'
a\#b: ; @echo 'H: $$@ = "$@"'
a$Eb: ; @echo 'I: $$@ = "$@"'
a\=b: ; @echo 'J: $$@ = "$@"'

wc1: m*d m\*d a\ b ; @echo '$@="$@";  $$^ = "$^"'
wc2: minion.md ; @echo '$$@ = "$@";  $$^ = "$^"'
wc3: a*b ; @echo '$$@ = "$@";  $$^ = "$^"'
wc\:x: ; @echo 'wcx1: $$@ = "$@";  $$^ = "$^"'     # make wc4:x
wc\\\:x: ; @echo 'wcx2: $$@ = "$@";  $$^ = "$^"'
#wc4: wc:x ; @echo '$$@ = "$@";  $$^ = "$^"' # ERROR: target pattern contains no %
wc5: wc\:x ; @echo '$$@ = "$@";  $$^ = "$^"'
wc7: a\b ; @echo '$$@ = "$@";  $$^ = "$^"'
wc8: a\#b ; @echo '$$@ = "$@";  $$^ = "$^"'
wc9: a\:b ; @echo '$$@ = "$@";  $$^ = "$^"'
wc10: a\=b ; @echo '$$@ = "$@";  $$^ = "$^"'