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.

https://github.com/rust-lang/rust/commit/eb01b17b06eb35542bb80ff7456043b0ed5572ba#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.

https://github.com/rust-lang/rust/commit/3f0cc8011aef3f530663302d525bd2d8cb493db5#diff-384affc1b4190940f114f3fcebbf969e7e18657a71ef9001da6b223a036687d9R1144

4 files changed, 30 insertions, 42 deletions

diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index d963d6092c4..f26d74629dd 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -1257,9 +1257,9 @@ impl clean::Impl {
                 };
                 primitive_link_fragment(f, PrimitiveType::Tuple, &format!("fn ({name}₁, {name}₂, …, {name}ₙ{ellipsis})"), "#trait-implementations-1", cx)?;
                 // Write output.
-                if let clean::FnRetTy::Return(ty) = &bare_fn.decl.output {
+                if !bare_fn.decl.output.is_unit() {
                     write!(f, " -> ")?;
-                    fmt_type(ty, f, use_absolute, cx)?;
+                    fmt_type(&bare_fn.decl.output, f, use_absolute, cx)?;
                 }
             } else if let Some(ty) = self.kind.as_blanket_ty() {
                 fmt_type(ty, f, use_absolute, cx)?;
@@ -1296,22 +1296,6 @@ impl clean::Arguments {
     }
 }
 
-impl clean::FnRetTy {
-    pub(crate) fn print<'a, 'tcx: 'a>(
-        &'a self,
-        cx: &'a Context<'tcx>,
-    ) -> impl fmt::Display + 'a + Captures<'tcx> {
-        display_fn(move |f| match self {
-            clean::Return(clean::Tuple(tys)) if tys.is_empty() => Ok(()),
-            clean::Return(ty) if f.alternate() => {
-                write!(f, " -> {:#}", ty.print(cx))
-            }
-            clean::Return(ty) => write!(f, " -&gt; {}", ty.print(cx)),
-            clean::DefaultReturn => Ok(()),
-        })
-    }
-}
-
 impl clean::BareFunctionDecl {
     fn print_hrtb_with_space<'a, 'tcx: 'a>(
         &'a self,
@@ -1366,7 +1350,7 @@ impl clean::FnDecl {
                     "({args:#}{ellipsis}){arrow:#}",
                     args = self.inputs.print(cx),
                     ellipsis = ellipsis,
-                    arrow = self.output.print(cx)
+                    arrow = self.print_output(cx)
                 )
             } else {
                 write!(
@@ -1374,7 +1358,7 @@ impl clean::FnDecl {
                     "({args}{ellipsis}){arrow}",
                     args = self.inputs.print(cx),
                     ellipsis = ellipsis,
-                    arrow = self.output.print(cx)
+                    arrow = self.print_output(cx)
                 )
             }
         })
@@ -1464,9 +1448,22 @@ impl clean::FnDecl {
             Some(n) => write!(f, "\n{})", Indent(n))?,
         };
 
-        fmt::Display::fmt(&self.output.print(cx), f)?;
+        fmt::Display::fmt(&self.print_output(cx), f)?;
         Ok(())
     }
+
+    pub(crate) fn print_output<'a, 'tcx: 'a>(
+        &'a self,
+        cx: &'a Context<'tcx>,
+    ) -> impl fmt::Display + 'a + Captures<'tcx> {
+        display_fn(move |f| match &self.output {
+            clean::Tuple(tys) if tys.is_empty() => Ok(()),
+            ty if f.alternate() => {
+                write!(f, " -> {:#}", ty.print(cx))
+            }
+            ty => write!(f, " -&gt; {}", ty.print(cx)),
+        })
+    }
 }
 
 pub(crate) fn visibility_print_with_space<'a, 'tcx: 'a>(
diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 42e27d35a94..a5223bd6309 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/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
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index ba0fc35bdbc..21f61acb2c5 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/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);
diff --git a/src/librustdoc/html/render/search_index.rs b/src/librustdoc/html/render/search_index.rs
index 846299f02e3..f34be120d29 100644
--- a/src/librustdoc/html/render/search_index.rs
+++ b/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)
 }