parseRoot

pub fn parseRoot(p: *Parse) Allocator.Error!void {
    // Root node must be index 0.
    p.nodes.appendAssumeCapacity(.{
        .tag = .root,
        .main_token = 0,
        .data = undefined,
    });
    const root_members = p.parseContainerMembers() catch |err| switch (err) {
        error.OutOfMemory => |e| return e,
        error.ParseError => {
            assert(p.errors.items.len > 0);
            return;
        },
    };
    const root_decls = try root_members.toSpan(p);
    if (p.tokenTag(p.tok_i) != .eof) {
        p.warnExpected(.eof) catch |err| switch (err) {
            error.OutOfMemory => |e| return e,
            error.ParseError => {
                assert(p.errors.items.len > 0);
                return;
            },
        };
    }
    p.nodes.items(.data)[0] = .{ .extra_range = root_decls };
}