No way to create a tuple with comptime fields using the new `@Tuple` builtin.

### Zig Version 0.16.0-dev.1470+32dc46aae ### Steps to Reproduce and Observed Behavior Hi there! I am writing a small game engine inspired in some ways by Bevy. The key feature is automatic, fully-comptime argument resolution for systems/functions using the `@typeInfo`, `@Type`, and `@call` builtins. However, while investigating how to port the codebase to the latest Zig version, I ran into a problem: it seems impossible to create a tuple with comptime fields using the new `@Tuple` builtin. This feature is required for comptime-only arguments resolution. Below is a heavily simplified version of the code currently used in my engine: ```zig fn system(a: u32, b: @TypeOf(.enum_lteral)) void { std.debug.print("Args values: {d} and {s}\n", .{ a, @tagName(b) }); } pub fn GetArgsTuple(func: anytype) type { const args = @typeInfo(@TypeOf(func)).@"fn".params; var args_array: [args.len]std.builtin.Type.StructField = undefined; inline for (args, 0..) |arg, i| { const ArgType = arg.type orelse unreachable; args_array[i] = if (ArgType == @TypeOf(.enum_lteral)) std.builtin.Type.StructField{ .name = std.fmt.comptimePrint("{d}", .{i}), .type = @TypeOf(.enum_lteral), .default_value_ptr = @ptrCast(&.hello), .alignment = @alignOf(@TypeOf(.enum_lteral)), .is_comptime = true, } else std.builtin.Type.StructField{ .name = std.fmt.comptimePrint("{d}", .{i}), .type = ArgType, .default_value_ptr = null, .alignment = @alignOf(ArgType), .is_comptime = false, }; } return @Type(.{ .@"struct" = std.builtin.Type.Struct{ .layout = .auto, .fields = &args_array, .decls = &.{}, .is_tuple = true, } }); } pub fn main() void { const ArgsTuple = comptime GetArgsTuple(system); var args: ArgsTuple = undefined; inline for (0..args.len) |i| { const ArgType = @TypeOf(args[i]); if (ArgType == @TypeOf(.enum_lteral)) { // allready provided continue; } else if (ArgType == u32) { args[i] = 2; } else unreachable; } @call(.auto, system, args); } const std = @import("std"); ``` Code snippet can be compiled using `0.15.0-dev.451+a843be44a`. P.S.: If there are any other possible ways to handle comptime argument resolution, let me know. ### Expected Behavior I expect that the rewriting should be done without losing **useful** functionality.