Rollup merge of #112113 - notriddle:notriddle/rm-fnretty, r=GuillaumeGomez

rustdoc: simplify `clean` by removing `FnRetTy`

The default fn ret ty is always unit. Just use that.

Looking back at the time when `FnRetTy` (then called `FunctionRetTy`) was first added to rustdoc, it seems to originally be there because `-> !` was a special form: the never type didn't exist back then.

eb01b17b06 (diff-384affc1b4190940f114f3fcebbf969e7e18657a71ef9001da6b223a036687d9L921-L924)

`DefaultReturn` was later added to rustdoc to mirror a change in HIR, which added a variant for DefaultReturn because it makes `Span` management easier. This isn't needed in rustdoc, since it doesn't carry spans.

3f0cc8011a (diff-384affc1b4190940f114f3fcebbf969e7e18657a71ef9001da6b223a036687d9R1144)

src/librustdoc/html/render/mod.rs

@@ -844,7 +844,7 @@ fn assoc_method(
         + name.as_str().len()
         + generics_len;
 
-    let notable_traits = d.output.as_return().and_then(|output| notable_traits_button(output, cx));
+    let notable_traits = notable_traits_button(&d.output, cx);
 
     let (indent, indent_str, end_newline) = if parent == ItemType::Trait {
         header_len += 4;
@@ -1282,6 +1282,11 @@ fn should_render_item(item: &clean::Item, deref_mut_: bool, tcx: TyCtxt<'_>) ->
 pub(crate) fn notable_traits_button(ty: &clean::Type, cx: &mut Context<'_>) -> Option<String> {
     let mut has_notable_trait = false;
 
+    if ty.is_unit() {
+        // Very common fast path.
+        return None;
+    }
+
     let did = ty.def_id(cx.cache())?;
 
     // Box has pass-through impls for Read, Write, Iterator, and Future when the

src/librustdoc/html/render/print_item.rs

@@ -587,8 +587,7 @@ fn item_function(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, f: &cle
         + name.as_str().len()
         + generics_len;
 
-    let notable_traits =
-        f.decl.output.as_return().and_then(|output| notable_traits_button(output, cx));
+    let notable_traits = notable_traits_button(&f.decl.output, cx);
 
     wrap_item(w, |w| {
         w.reserve(header_len);

src/librustdoc/html/render/search_index.rs

@@ -7,7 +7,7 @@ use rustc_span::symbol::Symbol;
 use serde::ser::{Serialize, SerializeStruct, Serializer};
 
 use crate::clean;
-use crate::clean::types::{FnRetTy, Function, Generics, ItemId, Type, WherePredicate};
+use crate::clean::types::{Function, Generics, ItemId, Type, WherePredicate};
 use crate::formats::cache::{Cache, OrphanImplItem};
 use crate::formats::item_type::ItemType;
 use crate::html::format::join_with_double_colon;
@@ -656,22 +656,9 @@ fn get_fn_inputs_and_outputs<'tcx>(
     }
 
     let mut ret_types = Vec::new();
-    match decl.output {
-        FnRetTy::Return(ref return_type) => {
-            add_generics_and_bounds_as_types(
-                self_,
-                generics,
-                return_type,
-                tcx,
-                0,
-                &mut ret_types,
-                cache,
-            );
-            if ret_types.is_empty() {
-                ret_types.push(get_index_type(return_type, vec![]));
-            }
-        }
-        _ => {}
-    };
+    add_generics_and_bounds_as_types(self_, generics, &decl.output, tcx, 0, &mut ret_types, cache);
+    if ret_types.is_empty() {
+        ret_types.push(get_index_type(&decl.output, vec![]));
+    }
     (all_types, ret_types)
 }