Can't you just do if (DEFINED Halide_VERSION_OVERRIDE)?

No, because, as a cache variable, it is always defined.

I guess it might suffice to initialize it to the default and use it unconditionally?

Ah, wait this patch is still wrong because I need a way to include no information at all.

I think this is better now, @LebedevRI

I think this is less messy, but there's an issue.
I currently do pass -DHalide_VERSION_OVERRIDE="",
in order to end up with libhalide<major>.so.<soversion> + libhalide<major>.so (symlink to former)...
I would really suggest if(DEFINED <???>) (i.e. use any override
without any attempts at verifying it), but in the end it doesn't matter.

As i've said, for all i care, this patch is unnessesary, i will still have to patch stuff on the packaging side.

If you set VERSION to the empty string and set SOVERSION to something meaningful, you get:

libHalide..dylib  # real lib
libHalide.19.dylib -> libHalide.dylib
libHalide.dylib -> libHalide.19.dylib

That first entry, with the truly empty version component, is insane.

I agree it is, but that is not what i get here. That insanity might be osx-specific.

If you leave VERSION undefined, however, you get what you described:

No, i don't. I need major version to be a suffix of the name, without .-separator.

No, i don't. I need major version to be a suffix of the name, without .-separator.

What you're describing here would be something like CMAKE_RELEASE_POSTFIX, no?

Docs: https://cmake.org/cmake/help/latest/variable/CMAKE_CONFIG_POSTFIX.html

With this patch, you can set:

-DCMAKE_RELEASE_POSTFIX=19 -DHalide_VERSION_OVERRIDE="" -DHalide_SOVERSION_OVERRIDE=0

I get libHalide19.0.so and a symlink to it called libHalide19.so.

Maybe.

Let me put it another way: why must this cmakefile refuse to take "" as valid version/soversion override?

It doesn't have to, but it has to make some compromise between:

1. Defaulting to having a VERSION and SOVERSION
2. Enabling users to conveniently override "not defined"
3. Enabling users to conveniently override to "empty string"

I'm not willing to compromise on (1) because having library versions is the correct default for too many users. So then in order to override, the override variable must be defined. If it's defined, how should I specify that I should remove the VERSION and SOVERSION properties, as I need to do for pip packaging? I can either:

1. Use <empty> as a special value leading to the empty string and let an empty string lead to undefined.
2. Use <undef> as a special value leading to undefined and let an empty string be an empty string.

The mathematician in me likes (2) because "an empty string [should] be an empty string". However, I chose (1) because of the vexing .. behavior. I still haven't seen a use for the empty string that isn't covered by CMAKE_RELEASE_POSTFIX. Well, I didn't quite choose (1) because I didn't implement <empty>, but again, I haven't seen a need.

You clearly have a reason, otherwise we wouldn't be in this discussion. Can you enlighten me?