Sema: disallow @intFromPtr to accept comptime-only types

[wrongnull]

It would make a lot more sense if we prevented it from accepting pointers to comptime-only types.

[wrongnull]

It looks like anytype parameters are treated as comptime-only under any conditions. @Vexu , is it a bug? If so, I could open an issue and try to fix one.

[Vexu]

No, this just has the same bug that you fixed for @extern in #17509. Also @SpexGuy was against this change when I previously tried to implement it in #11734 (comment).

[mlugg]

Also @SpexGuy was against this change when I previously tried to implement it in #11734 (comment).

AFAICT that's about something else. @intFromPtr on pointers to comptime memory where the child type is not comptime-only could, in theory, be implemented in a semi-sane way using lazy values or something (although I still don't think that's a worthwhile idea). However, this is about @intFromPtr on an actual comptime-only type, where having a concrete address is just a nonsensical concept - it's not like you could ever perform meaningful arithmetic on that address, since the value doesn't have a size.

Currently, it seems backends (or at least LLVM) just lower these values as references to zero-bit types (so give them an arbitrary "fake address"), which is an entirely useless and unintuitive behavior.

[andrewrk]

Thanks! After a minor rewording of the error message, this is ready to land.

[andrewrk]

Suggested change

	const msg = try sema.errMsg(block, ptr_src, "cannot accept pointer to comptime-only type '{}'", .{pointee_ty.fmt(mod)});
	const msg = try sema.errMsg(block, ptr_src, "comptime-only type '{}' has no pointer address", .{pointee_ty.fmt(mod)});

[wrongnull]

[wrongnull]

@andrewrk Is it worth mentioning this in the langref?