IMHO it is OK if you are only going to call a few simple one, but for calling a few hundred complex ones (callbacks with variable argument list, etc..), it becomes a bit cumbersome.

BTW I am not implying that is Rust's fault, actually I can't think a syntax that would make it less verbose, and I am a huge Rust fan.

Not really, there are tools that can take C header files and spit out bindings. Rust also supports vararg C functions even though Rust itself doesn't support varargs. Writing safe Rust wrappers around these unsafe C bindings can sometimes be tedious, but this isn't worse than using C directly (which is inherently unsafe).

I didn't say it is not supporting them. I said that is a bit cumbersome to have to write the shims for them.

I wasn't aware of the tools that do this automatically. Just found one and it looks promising.

Yeah, my point was that thin shims are free, and "thick" safe shims take effort but as far as comparing with pure C is concerned you only need to compare the cost of thin shims. C doesn't have safety so the concept of a thick, safe shim is nonexistant.

For very extensive C APIs like this (Lua, GTK, etc.) we typically see people create thin, Rust-friendly wrappers to reduce the amount of manual API calls that need to be written out.