Succinctly adding verbose output to GNU make - makefile

Question

I would like to add verbose output to a gnu makefile if V=1 is passed on the command line.
I can already do it in three lines as follows:
ifeq ($(V),1)
$(info SRC_FILES=$(SRC_FILES))
endif
Is there some more terse idiom, e.g., that appears all on one line? Ideally I'd like something like:
$(verbose SRC_FILES=$(SRC_FILES))
which may not be possible, or at least a one-liner like:
$(if $(V) $(info SRC_FILES=$(SRC_FILES)))

Answer 1

$(info $(if $(V),SRC_FILES=$(SRC_FILES))) almost does what you want. Its only drawback is that it outputs an empty line when V is undefined.
EDIT: from MadScientist's remark, and as initially suggested by BeeOnRope, $(if $(V),$(info SRC_FILES=$(SRC_FILES))) works exactly as expected, without the empty line when V is undefined.
You could also define a macro that prints an info message about a variable if and only if V is defined:
define verbose
$(if $(V),$(info $(1) = $($(1))))
endef
$(call verbose,SRC_FILES)
Of course, if you want a more generic macro, you can pass it the text to print:
define verbose
$(if $(V),$(info $(1)))
endef
$(call verbose,SRC_FILES = $(SRC_FILES))
Note that there are other types of information that you may want to control with a verbosity level variable. For the commands echoing, the commands outputs and the quiet command options I frequently use the following:
# Verbosity
ifeq ($(V),)
Q := #
MQ := --quiet
ECHO := echo
OUT := &> /dev/null
else ifeq ($(V),1)
Q :=
MQ :=
ECHO := echo
OUT :=
else
$(error V: invalid value ($(V)))
endif
foo:
$(Q)$(ECHO) 'making $#' && \
some-command $# $(OUT)
bar: cuz
$(Q)$(MAKE) $(MQ) $#
...

Answer 2

Maybe this will be practical:
verbose = $(if $(VERBOSITY),$(info $(-verbose)))
-verbose = $(if $(findstring 0,$(VERBOSITY)),$1 )$(if $(findstring 1,$(VERBOSITY)),$2 )$(if $(findstring 2,$(VERBOSITY)),$3 )$(if $(findstring 3,$(VERBOSITY)),$4 )$(if $(findstring 4,$(VERBOSITY)),$5 )$(if $(findstring 5,$(VERBOSITY)),$6 )$(if $(findstring 6,$(VERBOSITY)),$7 )$(if $(findstring 7,$(VERBOSITY)),$8 )$(if $(findstring 8,$(VERBOSITY)),$9 )$(if $(findstring 9,$(VERBOSITY)),$(10) )
VERBOSITY = 0
$(call verbose,warninglevel 1,warninglevel 2,warninglevel 3,info 1,info 2,info 3)
VERBOSITY = 2
$(call verbose,warninglevel 1,warninglevel 2,warninglevel 3,info 1,info 2,info 3)
VERBOSITY = 012345
$(call verbose,warninglevel 1,warninglevel 2,warninglevel 3,info 1,info 2,info 3)
Output:
warninglevel 1
warninglevel 3
warninglevel 1 warninglevel 2 warninglevel 3 info 1 info 2 info 3
I have added it to gmtt.