Deserialization of comptime structs

[gballet]

This is a tracking issue for the following problem:

The implementation of structure deserialization uses a reference to @field, which is a runtime expression.

If a structure is declared const in a test, it will be comptime and this causes a problem where a reference to a comptime object is taken at runtime, which is not possible.

Reproduction of the problem:

const std = @import("std");
const builtin = @import("builtin");

pub fn main() !void {
    const mystruc = .{ .age = @as(u8, 5), .name = @as([]const u8, "roger") };
    const tinfo = @typeInfo(@TypeOf(mystruc));
    inline for (tinfo.Struct.fields) |field| {
    	const x = &@field(mystruc, field.name);
        std.debug.print("field = {any}\n", .{x});
    }
}

output:

prog.zig:11:45: error: runtime value contains reference to comptime var
/tmp/tmpdir_tg2Kt7nRRXakarUS/tmp_kfQvMGZT1vr00sIzprog.zig:11:45: note: comptime var pointers are not available at runtime

Update

Note that dereferencing the pointer works:

const std = @import("std");
const builtin = @import("builtin");

pub fn main() !void {
    const mystruc = .{ .age = @as(u8, 5), .name = @as([]const u8, "roger") };
    const tinfo = @typeInfo(@TypeOf(mystruc));
    inline for (tinfo.Struct.fields) |field| {
    	const x = &@field(mystruc, field.name);
        std.debug.print("field = {any}\n", .{x.*});
    }
}

output:

field = 5
field = { 114, 111, 103, 101, 114 }

which is normal, since there no longer is a reference during the comptime evaluation. So the workaround would be to somehow not pass a pointer in that case.

[gballet]

Clarification: the issue is that the reference to the field is taken at comptime, but it is used at runtime on out.*, which makes no sense as this is an entirely different context. The question is whether we can force the pointer to be taken at runtime?