Rust 当为a Self：IntoIterator设置trait bind `时，获取`a T `不是迭代器"&'"<'>&'

我试图用Higher-Rank Trait Bound定义一个trait Foo，在&'a Self类型IntoIterator上.换句话说，我想要求实现类型T可以通过不可变借位迭代(即，&T: IntoIterator).

我还想要一个函数bar，它接受类型为T: Foo的参数.但这给了我一个错误.

以下是MRE:(playground在夜间1.79)

trait Foo
where for<'a> &'a Self: IntoIterator
{}

fn bar<T: Foo>(_: T) {}

这就是错误:

error[E0277]: `&'a T` is not an iterator
 --> src/lib.rs:5:11
  |
5 | fn bar<T: Foo>(_: T) {}
  |           ^^^ `&'a T` is not an iterator
  |
  = help: the trait `for<'a> Iterator` is not implemented for `&'a T`, which is required by `for<'a> &'a T: IntoIterator`
  = help: the trait `Iterator` is implemented for `&mut I`
  = note: required for `&'a T` to implement `for<'a> IntoIterator`
note: required by a bound in `Foo`
 --> src/lib.rs:2:25
  |
1 | trait Foo
  |       --- required by a bound in this trait
2 | where for<'a> &'a Self: IntoIterator
  |                         ^^^^^^^^^^^^ required by this bound in `Foo`

For more information about this error, try `rustc --explain E0277`.

我不明白这个错误.为什么要用for<'a> Iterator来实现&'a T？Iteratortrait 似乎不是IntoIterator的超级trait .

为什么他说是"required for 100 to implement 101"？毕竟，这正是我为Foo定义的trait边界，也就是我为bar参数的类型设置的边界，不是吗？

我觉得我在这里错过了一些基本的东西，但这是一种罕见的情况，当我发现编译器的错误信息根本没有帮助时.

PS:

这句话更让人困惑:"the trait 100 is implemented for 101".I到底是什么？