GAT lifetime not added to 'de bounds

[tguichaoua]

I'm trying to use Generic Associated Types in structure that derive serde::Deserialize.

But because of the GAT the bound 'de: 'a is not added for A.

I know it's possible to use #[serde(bound = "'de: 'a")] but it's surprising the bounds used by GAT are ignored.

trait Trait {
    type Gat<'a>;
}

struct Foo;

impl Trait for Foo {
    type Gat<'a> = &'a str;
}

struct Goo;

impl Trait for Goo {
    type Gat<'a> = String;
}

#[derive(serde::Deserialize)]
struct A<'a> {
    x: <Foo as Trait>::Gat<'a>, // lifetime may not live long enough consider adding the following bound: `'de: 'a`
    y: <Goo as Trait>::Gat<'a>, // this one is OK
}

#[derive(serde::Deserialize)]
struct B<'a> {
    x: &'a str, // no problem when inlined
}

Output of cargo expand

impl<'de, 'a> _serde::Deserialize<'de> for A<'a> {
// ...
impl<'de: 'a, 'a> _serde::Deserialize<'de> for B<'a> {

[tguichaoua]

I check the docs and it's seems the solution is to use #[serde(borrow)].
https://serde.rs/lifetimes.html#borrowing-data-in-a-derived-impl