zon.stringify: tagged unions with void fields do not serialize

[NicoElbers]

Zig Version

0.14.0-dev.3241+55c46870b

Steps to Reproduce and Observed Behavior

mwe.zig:

 pub const foo = union(enum) {
    bar,
};

pub fn main() !void {
    const t: foo = .bar;

    std.zon.stringify.serialize(t, .{}, std.io.null_writer) catch unreachable;
}
const std = @import("std");

run: zig run mwe.zig

Observe:

zig run mwe.zig
/nix/store/4h7cpfzzsczh6g8ivdvaz5k9dygy5z6p-zig-0.14.0-dev.3241+55c46870b/lib/std/debug.zig:518:14: error: reached unreachable code
    if (!ok) unreachable; // assertion failure
             ^~~~~~~~~~~
/nix/store/4h7cpfzzsczh6g8ivdvaz5k9dygy5z6p-zig-0.14.0-dev.3241+55c46870b/lib/std/zon/stringify.zig:493:28: note: called from here
            comptime assert(canSerializeType(@TypeOf(val)));
                     ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
referenced by:
    fieldArbitraryDepth__anon_6382: /nix/store/4h7cpfzzsczh6g8ivdvaz5k9dygy5z6p-zig-0.14.0-dev.3241+55c46870b/lib/std/zon/stringify.zig:1005:56
    fieldArbitraryDepth__anon_4262: /nix/store/4h7cpfzzsczh6g8ivdvaz5k9dygy5z6p-zig-0.14.0-dev.3241+55c46870b/lib/std/zon/stringify.zig:907:55
    9 reference(s) hidden; use '-freference-trace=11' to see all references

Expected Behavior

A union with a void field should serialize

[NicoElbers]

I have a patch here that would solve serialization, at least generating valid zig code, but it uses a void literal which then doesn't de-serialize.

Here the patch

diff --git a/lib/std/zon/stringify.zig b/lib/std/zon/stringify.zig
index a3f2b9cc00..9197c1dafc 100644
--- a/lib/std/zon/stringify.zig
+++ b/lib/std/zon/stringify.zig
@@ -504,7 +504,6 @@ pub fn Serializer(Writer: type) type {
                 .bool, .null => try std.fmt.format(self.writer, "{}", .{val}),
                 .enum_literal => try self.ident(@tagName(val)),
                 .@"enum" => try self.ident(@tagName(val)),
-                .void => try self.writer.writeAll("{}"),
                 .pointer => |pointer| {
                     // Try to serialize as a string
                     const item: ?type = switch (@typeInfo(pointer.child)) {
@@ -581,11 +580,14 @@ pub fn Serializer(Writer: type) type {
                     comptime assert(@"union".tag_type != null);
                     var container = try self.startStruct(.{ .whitespace_style = .{ .fields = 1 } });
                     switch (val) {
-                        inline else => |pl, tag| try container.fieldArbitraryDepth(
-                            @tagName(tag),
-                            pl,
-                            options,
-                        ),
+                        inline else => |pl, tag| try if (@TypeOf(pl) == void)
+                            self.writer.print(".{s} = {{}}", .{@tagName(tag)})
+                        else
+                            container.fieldArbitraryDepth(
+                                @tagName(tag),
+                                pl,
+                                options,
+                            ),
                     }
                     try container.finish();
                 },

To do this properly under the current system you would have to check if the child type is a union and if its child type is void, otherwise things get wrapped in .{ } (forcing the usage of a void literal)

@as(Foo, .bar)

Deserializes to:

.{.bar = {}}

However:

1:10: error: void literals are not available in ZON
1:10: note: void union payloads can be represented by enum literals

Ignore all that, I cannot read code