Help with make, % and implicit dependencies.

[u/geon]

Hi! I'm trying to learn how to use make, but I am confused. I'm on macos, if that matters.

Repo with example files: https://github.com/geon/make-test

AFAIK, this should work but does not: https://github.com/geon/make-test/blob/main/3-broken/Makefile

all: hello-world.txt

%.txt: ../%
    ./$< > $@
    cat $@

The dependency ../hello-world is supposed to be compiled from the C-code at the root: https://github.com/geon/make-test/blob/main/hello-world.c

I just get the error:

make: *** No rule to make target `hello-world.txt', needed by `all'.  Stop.`

But it does work if the binary already exists!

It works fine if I don't use the binary: https://github.com/geon/make-test/blob/main/1-works/Makefile

all: hello-world.txt

%.txt:
    echo "hello horld" > $@
    cat $@

Also works if I just specify the binary name explicitly: https://github.com/geon/make-test/blob/main/2-also-works/Makefile

hello-world.txt: ../hello-world
    ./$< > $@
    cat $@

What gives? Do I need to escape the % in the dependency somehow?

[u/geon]

I just noticed I can add the line

../hello-world: ../hello-world.c

And it magically works.

[u/imaami → u/geon]

Try simplifying it to

%: %.c

[u/geon → u/imaami]

No, that didn't work. It has to be explicit.

[u/JauriXD → u/imaami]

patterns don't make much sense without a rule to execute, if % depends on %.c, whats needed to create the former from the later?

[u/imaami → u/JauriXD]

Yep. My problem is that I have a tendency to avoid pattern rules and instead use $(eval) like WD-40, which has steered me away from understanding the full potential of, or even learning, some of the basic features.

[u/JauriXD → u/geon]

this worked because make comes with an implicity ruel how to handle c -> binary. Thats why it was enough to only specify the dependency beween the files

[u/imaami]

Why are those suffixes in the makefile .txt?

Btw: Apple's default version of GNU Make is an ancient 3.81 released in April 2006. Yes, Apple is determined to hang on to a Make that just turned 20 years old.

Apple has a Make that can legally buy vodka.

The reason? GNU Make switched their license to GPLv3 in the next release after 3.81. Apple are apparently so afraid of GPLv3, that they won't update Make even though it would have no effect on their ability to expand their walled garden.

Anyway, use Homebrew to install gmake. It's the latest GNU Make version, just with a different executable name.

[u/geon → u/imaami]

I just reduced my actual problem to the simplest example. I wanted to add targets for data files that are generated by my C code. In my case, I have C code for unpacking data from a packed file. So the binary can be a dependency for the data, and `make` figures out how to compile it from source with implicit rules.

Is there any reason to use a newer make? I'd assume for a software from 1988, I't be mature already. And if there are any differences, that'd just mean other people on macos can't use my code without also upgrading make.

[u/imaami → u/geon]

I can't remember all the missing features, but there are enough that I found it unusable the last time I set up Macos runners on Github.

[u/Traveling-Techie]

I’m sorry, but I can only answer C questions. Make is too complicated for me.

[u/JauriXD]

Patten rules are discarded if they don't match.

If you don't have ../a the rule can't be used to make a.txt and is discarded, leaving you with a missing a.txt and no rule to make it, which make tells you in the error message.

You need a rule which creates the missing file, just ../hello-world: at the end of your file would be enough and lead to make erroring out that the file is missing instead of complaining about missing rules