either move callconv to be just after fn keyword, or put comptime arguments in scope of callconv expression

[alexnask]

Example:

fn foo(comptime flag: bool) callconv(if (flag) .Unspecified else .Async) void {}

test "" {
    // Yields: "error: use of undeclared identifier 'flag'"
    foo(true);
}

[LemonBoy]

That's intended (I can vouch for the callconv parameter at least), the callconv and align are evaluated in the scope containing the function and independently from its parameters.

[alexnask]

Fair enough, closing this.

[andrewrk]

Hang on, the whole point of having callconv after the parameters rather than after the fn keyword is so that it would make sense for the comptime parameters to be in scope.

I actually thought they were in scope until just now. So one of two things needs to happen:

• Decide that comptime args will not be in spec for callconv purposes (status quo), and therefore move callconv to be after the `fn keyword, or
• Change the callconv expression to have comptime parameters in scope

I propose the latter, to match align.

#4285

I'll second #4285. I've worked out a way to make it non-breaking, and it has a whole lot of other benefits as well.