421a2113a8
show in docs whether the return type of a function impls Iterator/Read/Write Closes #25928 This PR makes it so that when rustdoc documents a function, it checks the return type to see whether it implements a handful of specific traits. If so, it will print the impl and any associated types. Rather than doing this via a whitelist within rustdoc, i chose to do this by a new `#[doc]` attribute parameter, so things like `Future` could tap into this if desired. ### Known shortcomings ~~The printing of impls currently uses the `where` class over the whole thing to shrink the font size relative to the function definition itself. Naturally, when the impl has a where clause of its own, it gets shrunken even further:~~ (This is no longer a problem because the design changed and rendered this concern moot.) The lookup currently just looks at the top-level type, not looking inside things like Result or Option, which renders the spotlights on Read/Write a little less useful: <details><summary>`File::{open, create}` don't have spotlight info (pic of old design)</summary>  </details> All three of the initially spotlighted traits are generically implemented on `&mut` references. Rustdoc currently treats a `&mut T` reference-to-a-generic as an impl on the reference primitive itself. `&mut Self` counts as a generic in the eyes of rustdoc. All this combines to create this lovely scene on `Iterator::by_ref`: <details><summary>`Iterator::by_ref` spotlights Iterator, Read, and Write (pic of old design)</summary>  </details> |
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| .. | ||
| iterator.rs | ||
| mod.rs | ||
| range.rs | ||
| sources.rs | ||
| traits.rs | ||
