[tavianator]

Nice! I used to do something similar, don't remember exactly why I had to switch but the two step process did become necessary at some point.

Just from a quick peek at that repo, nowadays you can write

#if __has_attribute(cold)

and avoid the configure test entirely. Probably wasn't a thing 10 years ago though :)

[o11c]

The problem is that the various `__has_foo` aren't actually reliable in practice - they don't tell you if the attribute, builtin, include, etc. actually works the way it's supposed to without bugs, or if it includes a particular feature (accepts a new optional argument, or allows new values for an existing argument, etc.).

[aaronmdjones]

    #if __has_attribute(cold)

You should use double underscores on attribute names to avoid conflicts with macros (user-defined macros beginning with double underscores are forbidden, as identifiers beginning with double underscores are reserved).

    #if __has_attribute(__cold__)
    #  warning "This works too"
    #endif

    static void __attribute__((__cold__))
    foo(void)
    {
        // This works too
    }

[codys]

yep. C's really come a long way with the special operators for checking if attributes exist, if builtins exist, if headers exist, etc.

Covers a very large part of what is needed, making fewer and fewer things need to end up in configure scripts. I think most of what's left is checking for items (types, functions) existence and their shape, as you were doing :). I can dream about getting a nice special operator to check for fields/functions, would let us remove even more from configure time, but I suspect we won't because that requires type resolution and none of the existing special operators do that.

[mikepurvis]

You still need a configure step for the "where are my deps" part of it, though both autotools and CMake would be way faster if all they were doing was finding, and not any testing.