UnionDecl

    pub const UnionDecl = struct {
        // These fields should be concatenated and reinterpreted as a `std.zig.SrcHash`.
        // This hash contains the source of all fields, and any specified attributes (`extern` etc).
        fields_hash_0: u32,
        fields_hash_1: u32,
        fields_hash_2: u32,
        fields_hash_3: u32,
        src_line: u32,
        src_column: u32,
        /// This node provides a new absolute baseline node for all instructions within this struct.
        src_node: Ast.Node.Index,

        pub const Small = packed struct(u16) {
            has_captures_len: bool,
            has_decls_len: bool,
            has_fields_len: bool,
            name_strategy: NameStrategy,
            kind: Kind,
            any_field_aligns: bool,
            any_field_values: bool,
            _: u6 = 0,
        };

        pub const Kind = enum(u3) {
            /// `union`
            auto,
            /// `union(T)`
            tagged_explicit,
            /// `union(enum)`
            tagged_enum,
            /// `union(enum(T))`
            tagged_enum_explicit,
            /// `extern union`
            @"extern",
            /// `packed union`
            @"packed",
            /// `packed union(T)`
            packed_explicit,

            pub fn hasArgType(k: Kind) bool {
                return switch (k) {
                    .auto, .tagged_enum, .@"extern", .@"packed" => false,
                    .tagged_explicit, .tagged_enum_explicit, .packed_explicit => true,
                };
            }

            pub fn layout(k: Kind) std.lang.Type.ContainerLayout {
                return switch (k) {
                    .auto, .tagged_explicit, .tagged_enum, .tagged_enum_explicit => .auto,
                    .@"extern" => .@"extern",
                    .@"packed", .packed_explicit => .@"packed",
                };
            }
        };
    }