Rollup merge of rust-lang#69514 - GuillaumeGomez:remove-spotlight, r=kinnison

Remove spotlight

I had a few comments saying that this feature was at best misunderstood or not even used so I decided to organize a poll about on [twitter](https://twitter.com/imperioworld_/status/1232769353503956994). After 87 votes, the result is very clear: it's not useful. Considering the amount of code we have just to run it, I think it's definitely worth it to remove it.

r? @kinnison

cc @ollie27

Author: Centril

src/doc/rustdoc/src/unstable-features.md

@@ -138,27 +138,6 @@ Book][unstable-doc-cfg] and [its tracking issue][issue-doc-cfg].
 [unstable-doc-cfg]: ../unstable-book/language-features/doc-cfg.html
 [issue-doc-cfg]: https://github.com/rust-lang/rust/issues/43781
 
-### Adding your trait to the "Important Traits" dialog
-
-Rustdoc keeps a list of a few traits that are believed to be "fundamental" to a given type when
-implemented on it. These traits are intended to be the primary interface for their types, and are
-often the only thing available to be documented on their types. For this reason, Rustdoc will track
-when a given type implements one of these traits and call special attention to it when a function
-returns one of these types. This is the "Important Traits" dialog, visible as a circle-i button next
-to the function, which, when clicked, shows the dialog.
-
-In the standard library, the traits that qualify for inclusion are `Iterator`, `io::Read`, and
-`io::Write`. However, rather than being implemented as a hard-coded list, these traits have a
-special marker attribute on them: `#[doc(spotlight)]`. This means that you could apply this
-attribute to your own trait to include it in the "Important Traits" dialog in documentation.
-
-The `#[doc(spotlight)]` attribute currently requires the `#![feature(doc_spotlight)]` feature gate.
-For more information, see [its chapter in the Unstable Book][unstable-spotlight] and [its tracking
-issue][issue-spotlight].
-
-[unstable-spotlight]: ../unstable-book/language-features/doc-spotlight.html
-[issue-spotlight]: https://github.com/rust-lang/rust/issues/45040
-
 ### Exclude certain dependencies from documentation
 
 The standard library uses several dependencies which, in turn, use several types and traits from the

src/doc/unstable-book/src/language-features/doc-spotlight.md

@@ -24,7 +24,6 @@ use crate::task::{Context, Poll};
 /// `.await` the value.
 ///
 /// [`Waker`]: ../task/struct.Waker.html
-#[doc(spotlight)]
 #[must_use = "futures do nothing unless you `.await` or poll them"]
 #[stable(feature = "futures_api", since = "1.36.0")]
 #[lang = "future_trait"]

src/libcore/future/future.rs

@@ -92,7 +92,6 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
     label = "`{Self}` is not an iterator",
     message = "`{Self}` is not an iterator"
 )]
-#[doc(spotlight)]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 pub trait Iterator {
     /// The type of the elements being iterated over.

src/libcore/iter/traits/iterator.rs

@@ -90,7 +90,6 @@
 #![feature(custom_inner_attributes)]
 #![feature(decl_macro)]
 #![feature(doc_cfg)]
-#![feature(doc_spotlight)]
 #![feature(extern_types)]
 #![feature(fundamental)]
 #![feature(intrinsics)]

src/libcore/lib.rs

@@ -245,7 +245,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                     include => external_doc
                     cfg => doc_cfg
                     masked => doc_masked
-                    spotlight => doc_spotlight
                     alias => doc_alias
                     keyword => doc_keyword
                 );

src/librustc_ast_passes/feature_gate.rs

@@ -360,9 +360,6 @@ declare_features! (
     /// Allows `#[doc(masked)]`.
     (active, doc_masked, "1.21.0", Some(44027), None),
 
-    /// Allows `#[doc(spotlight)]`.
-    (active, doc_spotlight, "1.22.0", Some(45040), None),
-
     /// Allows `#[doc(include = "some-file")]`.
     (active, external_doc, "1.22.0", Some(44732), None),
 

src/librustc_feature/active.rs

@@ -270,7 +270,6 @@ symbols! {
         doc_cfg,
         doc_keyword,
         doc_masked,
-        doc_spotlight,
         doctest,
         document_private_items,
         dotdoteq_in_patterns,
@@ -689,7 +688,6 @@ symbols! {
         Some,
         specialization,
         speed,
-        spotlight,
         sse4a_target_feature,
         stable,
         staged_api,

src/librustc_span/symbol.rs

@@ -198,15 +198,13 @@ pub fn build_external_trait(cx: &DocContext<'_>, did: DefId) -> clean::Trait {
     let generics = (cx.tcx.generics_of(did), predicates).clean(cx);
     let generics = filter_non_trait_generics(did, generics);
     let (generics, supertrait_bounds) = separate_supertrait_bounds(generics);
-    let is_spotlight = load_attrs(cx, did).clean(cx).has_doc_flag(sym::spotlight);
     let is_auto = cx.tcx.trait_is_auto(did);
     clean::Trait {
         auto: auto_trait,
         unsafety: cx.tcx.trait_def(did).unsafety,
         generics,
         items: trait_items,
         bounds: supertrait_bounds,
-        is_spotlight,
         is_auto,
     }
 }

src/librustdoc/clean/inline.rs

@@ -1013,7 +1013,6 @@ impl Clean<FnRetTy> for hir::FnRetTy<'_> {
 impl Clean<Item> for doctree::Trait<'_> {
     fn clean(&self, cx: &DocContext<'_>) -> Item {
         let attrs = self.attrs.clean(cx);
-        let is_spotlight = attrs.has_doc_flag(sym::spotlight);
         Item {
             name: Some(self.name.clean(cx)),
             attrs,
@@ -1028,7 +1027,6 @@ impl Clean<Item> for doctree::Trait<'_> {
                 items: self.items.iter().map(|ti| ti.clean(cx)).collect(),
                 generics: self.generics.clean(cx),
                 bounds: self.bounds.clean(cx),
-                is_spotlight,
                 is_auto: self.is_auto.clean(cx),
             }),
         }