Why are supertraits weird?

[acidoglutammico]

Why does the first compile and the second not?

Rust Playground

Rust Playground

I have two traits and i want one to require the first. The first trait requires for the type to implement IntoIterator for &Self (not Self, so that i can use iter() or implement it later for all T that have that trait). But I have to specify again where for<'a> &'a Self: IntoIterator, in the second trait.
Since i have other traits that require the basic trait I dont want to clutter all the code with bounds that are required in some mod far from the actual code.

[nerditation]

the short answer is the where clause of &'a Self is not a super trait, so it is not propagated.

see also discussion in this previous post:

Where clause in trait definition must be copied to where the trait is used?

This is a case of non-supertrait bounds not being elaborated elsewhere. That is, here: trait DeserRefer: Refer where for<'de> Self::Ref<'de>: Deserialize<'de> {} The where clause is not considered supertrait bound (a bound on Self).[1] If you don't have to worry about MSRV, we recently got the ability to make bounds on associated types of Self into bounds on Self, thus making them supertrait bounds which are implied elsewhere: // Inline associated type bound vvvvvvvvvvvvvvvvvvvvvvvvvv…

[acidoglutammico]

Thank you, searching for this stuff is hard, probably needs to be written somewhere on the wiki.