ExprKind::Tup(_elems) => { None }

ExprKind in rustc_hir

Call(&'hir Expr<'hir>, &'hir [Expr<'hir>])
A function call.

The first field resolves to the function itself (usually an ExprKind::Path), and the second field is the list of arguments. This also represents calling the constructor of tuple-like ADTs such as tuple structs and enum variants.

看起来你的匹配表达式需要返回一个 Option 类型，但是你的当前实现返回的是 () 类型（Rust的空类型）。你需要返回一个合适的 Option 类型，例如 None 或者 Some(T)，其中 T 是一个适合你程序的类型。

如果你没有合适的值要返回，你可以简单地返回 None，例如：

            ExprKind::Tup(_elems) => {
                // Do nothing for tuples, return None
                None
            }