rustdoc: fix cross-crate impl Sized & impl ?Sized

src/librustdoc/clean/mod.rs

@@ -835,7 +835,6 @@ fn clean_ty_generics<'tcx>(
                         .into_iter()
                         .flatten()
                         .cloned()
-                        .filter(|b| !b.is_sized_bound(cx)),
                 );
 
                 if let Some(proj) = projection
@@ -862,8 +861,27 @@ fn clean_ty_generics<'tcx>(
         .collect::<Vec<_>>();
 
     for (param, mut bounds) in impl_trait {
+        let mut has_sized = false;
+        bounds.retain(|b| {
+            if b.is_sized_bound(cx) {
+                has_sized = true;
+                false
+            } else {
+                true
+            }
+        });
+        if !has_sized {
+            bounds.push(GenericBound::maybe_sized(cx));
+        }
+
         // Move trait bounds to the front.
-        bounds.sort_by_key(|b| !matches!(b, GenericBound::TraitBound(..)));
+        bounds.sort_by_key(|b| !b.is_trait_bound());
+
+        // Add back a `Sized` bound if there are no *trait* bounds remaining (incl. `?Sized`).
+        // Since all potential trait bounds are at the front we can just check the first bound.
+        if bounds.first().map_or(true, |b| !b.is_trait_bound()) {
+            bounds.insert(0, GenericBound::sized(cx));
+        }
 
         let crate::core::ImplTraitParam::ParamIndex(idx) = param else { unreachable!() };
         if let Some(proj) = impl_trait_proj.remove(&idx) {
@@ -2107,7 +2125,6 @@ fn clean_middle_opaque_bounds<'tcx>(
     cx: &mut DocContext<'tcx>,
     bounds: Vec<ty::Clause<'tcx>>,
 ) -> Type {
-    let mut regions = vec![];
     let mut has_sized = false;
     let mut bounds = bounds
         .iter()
@@ -2116,10 +2133,7 @@ fn clean_middle_opaque_bounds<'tcx>(
             let trait_ref = match bound_predicate.skip_binder() {
                 ty::ClauseKind::Trait(tr) => bound_predicate.rebind(tr.trait_ref),
                 ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(_ty, reg)) => {
-                    if let Some(r) = clean_middle_region(reg) {
-                        regions.push(GenericBound::Outlives(r));
-                    }
-                    return None;
+                    return clean_middle_region(reg).map(GenericBound::Outlives);
                 }
                 _ => return None,
             };
@@ -2155,10 +2169,20 @@ fn clean_middle_opaque_bounds<'tcx>(
             Some(clean_poly_trait_ref_with_bindings(cx, trait_ref, bindings))
         })
         .collect::<Vec<_>>();
-    bounds.extend(regions);
-    if !has_sized && !bounds.is_empty() {
-        bounds.insert(0, GenericBound::maybe_sized(cx));
+
+    if !has_sized {
+        bounds.push(GenericBound::maybe_sized(cx));
     }
+
+    // Move trait bounds to the front.
+    bounds.sort_by_key(|b| !b.is_trait_bound());
+
+    // Add back a `Sized` bound if there are no *trait* bounds remaining (incl. `?Sized`).
+    // Since all potential trait bounds are at the front we can just check the first bound.
+    if bounds.first().map_or(true, |b| !b.is_trait_bound()) {
+        bounds.insert(0, GenericBound::sized(cx));
+    }
+
     ImplTrait(bounds)
 }
 

src/librustdoc/clean/types.rs

@@ -1219,15 +1219,24 @@ pub(crate) enum GenericBound {
 }
 
 impl GenericBound {
+    pub(crate) fn sized(cx: &mut DocContext<'_>) -> GenericBound {
+        Self::sized_with(cx, hir::TraitBoundModifier::None)
+    }
+
     pub(crate) fn maybe_sized(cx: &mut DocContext<'_>) -> GenericBound {
+        Self::sized_with(cx, hir::TraitBoundModifier::Maybe)
+    }
+
+    fn sized_with(cx: &mut DocContext<'_>, modifier: hir::TraitBoundModifier) -> GenericBound {
         let did = cx.tcx.require_lang_item(LangItem::Sized, None);
         let empty = ty::Binder::dummy(ty::GenericArgs::empty());
         let path = external_path(cx, did, false, ThinVec::new(), empty);
         inline::record_extern_fqn(cx, did, ItemType::Trait);
-        GenericBound::TraitBound(
-            PolyTrait { trait_: path, generic_params: Vec::new() },
-            hir::TraitBoundModifier::Maybe,
-        )
+        GenericBound::TraitBound(PolyTrait { trait_: path, generic_params: Vec::new() }, modifier)
+    }
+
+    pub(crate) fn is_trait_bound(&self) -> bool {
+        matches!(self, Self::TraitBound(..))
     }
 
     pub(crate) fn is_sized_bound(&self, cx: &DocContext<'_>) -> bool {

src/librustdoc/html/format.rs

@@ -1094,22 +1094,35 @@ fn fmt_type<'cx>(
             };
             let m = mutability.print_with_space();
             let amp = if f.alternate() { "&" } else { "&amp;" };
-            match **ty {
+
+            if let clean::Generic(name) = **ty {
+                return primitive_link(
+                    f,
+                    PrimitiveType::Reference,
+                    &format!("{amp}{lt}{m}{name}"),
+                    cx,
+                );
+            }
+
+            write!(f, "{amp}{lt}{m}")?;
+
+            let needs_parens = match **ty {
                 clean::DynTrait(ref bounds, ref trait_lt)
                     if bounds.len() > 1 || trait_lt.is_some() =>
                 {
-                    write!(f, "{}{}{}(", amp, lt, m)?;
-                    fmt_type(ty, f, use_absolute, cx)?;
-                    write!(f, ")")
-                }
-                clean::Generic(name) => {
-                    primitive_link(f, PrimitiveType::Reference, &format!("{amp}{lt}{m}{name}"), cx)
-                }
-                _ => {
-                    write!(f, "{}{}{}", amp, lt, m)?;
-                    fmt_type(ty, f, use_absolute, cx)
+                    true
                 }
+                clean::ImplTrait(ref bounds) if bounds.len() > 1 => true,
+                _ => false,
+            };
+            if needs_parens {
+                f.write_str("(")?;
             }
+            fmt_type(ty, f, use_absolute, cx)?;
+            if needs_parens {
+                f.write_str(")")?;
+            }
+            Ok(())
         }
         clean::ImplTrait(ref bounds) => {
             if f.alternate() {

tests/rustdoc/extern-impl-trait.rs

@@ -7,5 +7,5 @@ extern crate extern_impl_trait;
 // @has 'foo/struct.X.html' '//h4[@class="code-header"]' "impl Foo<Associated = ()> + 'a"
 pub use extern_impl_trait::X;
 
-// @has 'foo/struct.Y.html' '//h4[@class="code-header"]' "impl ?Sized + Foo<Associated = ()> + 'a"
+// @has 'foo/struct.Y.html' '//h4[@class="code-header"]' "impl Foo<Associated = ()> + ?Sized + 'a"
 pub use extern_impl_trait::Y;

tests/rustdoc/impl-everywhere.rs

@@ -25,6 +25,6 @@ pub fn foo_foo() -> impl Foo + Foo2 {
     Bar
 }
 
-// @has foo/fn.foo_foo_foo.html '//section[@id="main-content"]//pre' "x: &'x impl Foo + Foo2"
+// @has foo/fn.foo_foo_foo.html '//section[@id="main-content"]//pre' "x: &'x (impl Foo + Foo2)"
 pub fn foo_foo_foo<'x>(_x: &'x (impl Foo + Foo2)) {
 }

tests/rustdoc/inline_cross/auxiliary/impl-sized.rs

@@ -0,0 +1,21 @@
+use std::fmt::Debug;
+
+pub fn sized(x: impl Sized) -> impl Sized {
+    x
+}
+
+pub fn sized_outlives<'a>(x: impl Sized + 'a) -> impl Sized + 'a {
+    x
+}
+
+pub fn maybe_sized(x: &impl ?Sized) -> &impl ?Sized {
+    x
+}
+
+pub fn debug_maybe_sized(x: &(impl Debug + ?Sized)) -> &(impl Debug + ?Sized) {
+    x
+}
+
+pub fn maybe_sized_outlives<'t>(x: &(impl ?Sized + 't)) -> &(impl ?Sized + 't) {
+    x
+}

tests/rustdoc/inline_cross/impl-sized.rs

@@ -0,0 +1,27 @@
+#![crate_name = "user"]
+
+// aux-crate:impl_sized=impl-sized.rs
+// edition:2021
+
+// @has user/fn.sized.html
+// @has - '//pre[@class="rust item-decl"]' "sized(x: impl Sized) -> impl Sized"
+pub use impl_sized::sized;
+
+// @has user/fn.sized_outlives.html
+// @has - '//pre[@class="rust item-decl"]' \
+//     "sized_outlives<'a>(x: impl Sized + 'a) -> impl Sized + 'a"
+pub use impl_sized::sized_outlives;
+
+// @has user/fn.maybe_sized.html
+// @has - '//pre[@class="rust item-decl"]' "maybe_sized(x: &impl ?Sized) -> &impl ?Sized"
+pub use impl_sized::maybe_sized;
+
+// @has user/fn.debug_maybe_sized.html
+// @has - '//pre[@class="rust item-decl"]' \
+//     "debug_maybe_sized(x: &(impl Debug + ?Sized)) -> &(impl Debug + ?Sized)"
+pub use impl_sized::debug_maybe_sized;
+
+// @has user/fn.maybe_sized_outlives.html
+// @has - '//pre[@class="rust item-decl"]' \
+//     "maybe_sized_outlives<'t>(x: &(impl ?Sized + 't)) -> &(impl ?Sized + 't)"
+pub use impl_sized::maybe_sized_outlives;