make-3.79.1: embedded command prefix problems

[Philip Guenther]

The make info pages include the following quote under
Commands->Sequences:

-------
   In command execution, each line of a canned sequence is treated just
as if the line appeared on its own in the rule, preceded by a tab.  In
particular, `make' invokes a separate subshell for each line.  You can
use the special prefix characters that affect command lines (`@', `-',
and `+') on each line of a canned sequence.  *Note Writing the Commands
in Rules: Commands.  For example, using this canned sequence:

     define frobnicate
     @echo "frobnicating target $@"
     frob-step-1 $< -o address@hidden
     frob-step-2 address@hidden -o $@
     endef
-------

Okay, combining that with some good advice about automaticly generating
dependencies led to my writing the following variable definitions and
rules:

DEPEND_MUNGE    = dfile=$(basename $@).d Pfile=$(basename $@).P ; \
                  rm -f $$Pfile ; \
                  sed -e '1s:^:$(dir $@):' < $$dfile >$$Pfile ; \
                  sed -e 's/\#.*//' -e 's/^[^:]*: *//' -e 's/ *\\$$//' \
                        -e '/^$$/d' -e 's/$$/ :/' < $$dfile >>$$Pfile ; \
                  rm -f $$dfile
define COMPILEc
${CC} -c ${ALL_CPPFLAGS} ${LOCAL_CPPFLAGS} ${DEPEND} \
                ${ALL_CFLAGS} ${LOCAL_CFLAGS} -o $@ $<
@ ${DEPEND_MUNGE}
endef

That's then used in a series of pattern rules that look like:

${objdir}/%.o: ${srcdir}/%.c ; ${COMPILEc}


The problem is that sometimes, but not always, make will execute the
commands in ${COMPILEc} without echoing _any_ of them.  "make -n" shows
the correct output and tracing make shows that it really is executing
the commands.  Removing the '@' on the ${DEPEND_MUNGE} command makes
everything be echoed properly, so it is as if make sometimes 'leaks' an
embedded '@' prefix to apply to the entire variable.

What I find particularly bizarre is how it doesn't always do it.  Make
may need to build six files, all using the same pattern rule, but it'll
only show the ${CC} executing for one of the six.  Same directory, same
rule, same variable, different results.


For now I'm using the obvious workaround of changing COMPILEc to read:

define COMPILEc
@ echo ${CC} -c ${ALL_CPPFLAGS} ${LOCAL_CPPFLAGS} ${DEPEND} \
                ${ALL_CFLAGS} ${LOCAL_CFLAGS} -o $@ $<
@ ${CC} -c ${ALL_CPPFLAGS} ${LOCAL_CPPFLAGS} ${DEPEND} \
                ${ALL_CFLAGS} ${LOCAL_CFLAGS} -o $@ $<
@ ${DEPEND_MUNGE}
endef

which works just fine.


As a side note, writing DEPEND_MUNGE as a multiline variable definition
using define---endif doesn't appears to work for some other strange
reason.  At one point I was seeing two levels of make variable expansion
take place on it.  Trying it again now, I get "Recursive variable
`DEPEND_MUNGE' references itself (eventually)" errors, but I need to
play with it more to make sure I'm not confusing myself too.


Philip Guenther