Include generated makefile without warning message

Question

For a project of mine I am automatically generating makefiles and including them, like this:

all:
    @echo 'SUCCESS is $(SUCCESS)'

clean:
    rm depend.mk

depend.mk:
    @echo 'Creating $@'
    @echo 'SUCCESS := 1' > $@

.PHONY: all clean

include depend.mk

This works, but the include line generates a warning message:

$ make
Makefile:13: depend.mk: No such file or directory
Creating depend.mk
SUCCESS is 1

I would like to silence that first warning line saying that depend.mk doesn't exist. I know it doesn't exist since I have a rule written to generate it, so the warning is unnecessary (unless of course there isn't a rule for it). I do NOT want make to ignore the error where the included file doesn't exist and there is no rule for it, so prefixing include with a - to ignore the error will not work for me. I'd like something similar to bash's convention of piping stderr to /dev/null like some_cmd 2>/dev/null but for including in make.

The sample above is a very simplified example of this case. In my actual project there are a lot of automatically generated makefiles (via clang's automatic dependency generation) being included, meaning a fresh run of make will flood my screen with these warning messages.

Is anything like this possible, or am I just going to have to deal with the annoying warning messages?

Answer 1

I've encountered and (re-re-re-re-)solved this problem a number of times myself. Really, the problem is in the thinking surrounding when the dependency files are generated and used.

This link has the detailed description of the "resolution": http://make.mad-scientist.net/papers/advanced-auto-dependency-generation/

Basically it comes down to the fact that dependency files are really only necessary for rebuilding, not the initial building of your library/executable. Resultantly you don't need to have a rule for generating dependency files up front (which is in fact less efficient), you instead should generate them during the object file step as intermediate files marked precious (so they're created and tracked as side-effect files that should never be cleaned up automatically). Subsequent builds will then have the files available, which is exactly what you were trying to achieve overall. You can then make it a "-include" on the dependency files, with the foreknowledge that your object file build step will fail if the dependency file generation fails, giving an immediate error, as you've mentioned is preferred, rather than an obscure and indirect one much later.

I've actually done a couple rather large build systems implementing this method, and it does work quite well, including ones that used non-GNU toolchains. To an outside user it appears identical, but internally it performs more efficiently and isn't hiding potentially important errors.

Answer 2

I tried many (many!) things to see if I could prevent or redirect the error message. No luck.

But when I tried -include (include with a leading dash), it didn't give an error, and make with clean, all, depend.mk and 'default' all worked properly and as expected.

Is there a particular reason you didn't want to use the -include variant? Seems to do exactly what you're looking for, and doesn't alter how the Makefile works in any way, just doesn't show the error during the first pass through the Makefile.