How to debug my Makefile

[thutt]

Stefan Monnier writes:
 > My `make` complains that
 >
 >     make: execvp: /bin/sh: Argument list too long
 >     make: execvp: /bin/sh: Argument list too long
 >
 > but I'm having trouble figuring out which command's argument list is
 > too long.  I tried "make -d" but it doesn't really help:
 >
 >     % LANG=C make -d

 <snip>

 > As you can see, the error seems to be signaled "early".
 > How could I track it down?
 >


 If 'make -n' doesn't point out the long command line, then your
 diagnosis that it's the use of $(shell) is probably the culprit.


 > Looking at the make file I see one $(shell ..) invocation which is the
 > most likely culprit:
 >
 >     define SET-diff
 >     $(shell echo "$(1)" "$(2)" "$(2)" | tr ' ' '\n' | sort | uniq -u)
 >     endef

 Could you use a standard Make rule to generate an output file, and
 then use redirection to provide the output file to any programs.

 Within Gnu Make, it's pretty easy to $(sort) sort a list, but
 de-duplicating it is a bit tougher.  It could be done fairly easily
 with the associative arrays or sets in the Gnu Make Standard Library:

   https://gmsl.sourceforge.io/