.Pointer needs to go

Type.zig

// https://github.com/ziglang/zig/issues/10710#issue-1116978295

const std = @import("std");
const assert = std.debug.assert;

const TypeInfo = std.builtin.TypeInfo;

pub fn Type(comptime T: TypeInfo) type {
    return comptime switch (T) {
        // but what is the type of type?
        .Type => type,

        // won't work as the result is memoized :(
        .Opaque => opaque {},

        // the awkward
        .Struct => @Type(T),
        .Union => @Type(T),
        .Enum => @Type(T),
        .Int => @Type(T),
        .Fn => @Type(T),
        .Frame => |info| @Frame(info.function), // ???
        .ErrorSet => @Type(T), // sad:

        .BoundFn => @compileError("not loved anymore"),

        // the good stuff
        .Optional => |info| ?info.child,
        .AnyFrame => anyframe,
        .ComptimeFloat => comptime_float,
        .ComptimeInt => comptime_int,
        .Void => void,
        .Bool => bool,
        .NoReturn => noreturn,
        .Undefined => @TypeOf(undefined),
        .Null => @TypeOf(null),
        .EnumLiteral => @TypeOf(.magic),
        .Vector => |info| @Vector(info.len, info.child),
        .ErrorUnion => |info| info.error_set!info.payload,
        // :sad .ErrorSet => |info| @typeInfo(@TypeOf(hack(info orelse return error{}))).ErrorUnion.error_set,

        // cute
        .Array => |info| if (info.sentinel) |sentinel|
            [info.len:@ptrCast(*const info.child, sentinel).*]info.child
        else
            [info.len]info.child,

        .Float => |info| switch (info.bits) {
            16 => f16,
            32 => f32,
            64 => f64,
            80 => f80,
            128 => f128,
            else => @compileError("mate"),
        },

        // well, it's not that bad
        .Pointer => |info| {
            const pattern = //
                @as(u3, @boolToInt(info.is_volatile)) << 2 |
                @as(u3, @boolToInt(info.is_allowzero)) << 1 |
                @as(u3, @boolToInt(info.is_const));

            switch (info.size) {
                .One => return switch (pattern) {
                    0b111 => *allowzero align(info.alignment) addrspace(info.address_space) const volatile info.child,
                    0b011 => *allowzero align(info.alignment) addrspace(info.address_space) const info.child,
                    0b101 => *align(info.alignment) addrspace(info.address_space) const volatile info.child,
                    0b001 => *align(info.alignment) addrspace(info.address_space) const info.child,
                    0b110 => *allowzero align(info.alignment) addrspace(info.address_space) volatile info.child,
                    0b010 => *allowzero align(info.alignment) addrspace(info.address_space) info.child,
                    0b100 => *align(info.alignment) addrspace(info.address_space) volatile info.child,
                    0b000 => *align(info.alignment) addrspace(info.address_space) info.child,
                },
                .Many => {
                    if (info.sentinel) |tmp| {
                        const sentinel = @ptrCast(*const info.child, tmp).*;

                        return switch (pattern) {
                            0b111 => [*:sentinel]allowzero align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b011 => [*:sentinel]allowzero align(info.alignment) addrspace(info.address_space) const info.child,
                            0b101 => [*:sentinel]align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b001 => [*:sentinel]align(info.alignment) addrspace(info.address_space) const info.child,
                            0b110 => [*:sentinel]allowzero align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b010 => [*:sentinel]allowzero align(info.alignment) addrspace(info.address_space) info.child,
                            0b100 => [*:sentinel]align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b000 => [*:sentinel]align(info.alignment) addrspace(info.address_space) info.child,
                        };
                    } else {
                        return switch (pattern) {
                            0b111 => [*]allowzero align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b011 => [*]allowzero align(info.alignment) addrspace(info.address_space) const info.child,
                            0b101 => [*]align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b001 => [*]align(info.alignment) addrspace(info.address_space) const info.child,
                            0b110 => [*]allowzero align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b010 => [*]allowzero align(info.alignment) addrspace(info.address_space) info.child,
                            0b100 => [*]align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b000 => [*]align(info.alignment) addrspace(info.address_space) info.child,
                        };
                    }
                },
                .Slice => {
                    if (info.sentinel) |tmp| {
                        const sentinel = @ptrCast(*const info.child, tmp).*;

                        return switch (pattern) {
                            0b111 => [:sentinel]allowzero align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b011 => [:sentinel]allowzero align(info.alignment) addrspace(info.address_space) const info.child,
                            0b101 => [:sentinel]align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b001 => [:sentinel]align(info.alignment) addrspace(info.address_space) const info.child,
                            0b110 => [:sentinel]allowzero align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b010 => [:sentinel]allowzero align(info.alignment) addrspace(info.address_space) info.child,
                            0b100 => [:sentinel]align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b000 => [:sentinel]align(info.alignment) addrspace(info.address_space) info.child,
                        };
                    } else {
                        return switch (pattern) {
                            0b111 => []allowzero align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b011 => []allowzero align(info.alignment) addrspace(info.address_space) const info.child,
                            0b101 => []align(info.alignment) addrspace(info.address_space) const volatile info.child,
                            0b001 => []align(info.alignment) addrspace(info.address_space) const info.child,
                            0b110 => []allowzero align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b010 => []allowzero align(info.alignment) addrspace(info.address_space) info.child,
                            0b100 => []align(info.alignment) addrspace(info.address_space) volatile info.child,
                            0b000 => []align(info.alignment) addrspace(info.address_space) info.child,
                        };
                    }
                },
                .C => return switch (pattern) {
                    0b101 => [*c]align(info.alignment) addrspace(info.address_space) const volatile info.child,
                    0b001 => [*c]align(info.alignment) addrspace(info.address_space) const info.child,
                    0b100 => [*c]align(info.alignment) addrspace(info.address_space) volatile info.child,
                    0b000 => [*c]align(info.alignment) addrspace(info.address_space) info.child,
                    else => unreachable, // I can't be bothered to fix this
                },
            }
        },
    };
}

fn hack(comptime errors: []const TypeInfo.Error) !void {
    var x = false;
    inline for (errors) |err| {
        if (x) return @field(anyerror, err.name); // sue me
    }
}

test {
    const everything = *allowzero align(32) addrspace(.generic) const volatile u8;
    const shorttype = [*:32]allowzero align(32) addrspace(.generic) const volatile u32;

    comptime assert(Type(@typeInfo(everything)) == everything);
    comptime assert(Type(@typeInfo(shorttype)) == shorttype);
    comptime assert(*const u8 == Type(@typeInfo(*const u8)));
}