Fix redundant arguments in external_path()

If the path is for a trait, it is always true that `trait_did ==
Some(did)`, so instead, `external_path()` now takes an `is_trait`
boolean.

src/librustdoc/clean/mod.rs

@@ -164,14 +164,8 @@ impl Clean<Type> for (ty::TraitRef<'_>, &[TypeBinding]) {
             );
         }
         inline::record_extern_fqn(cx, trait_ref.def_id, kind);
-        let path = external_path(
-            cx,
-            trait_ref.def_id,
-            Some(trait_ref.def_id),
-            true,
-            bounds.to_vec(),
-            trait_ref.substs,
-        );
+        let path =
+            external_path(cx, trait_ref.def_id, true, true, bounds.to_vec(), trait_ref.substs);
 
         debug!("ty::TraitRef\n  subst: {:?}\n", trait_ref.substs);
 
@@ -1448,12 +1442,12 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                     AdtKind::Enum => ItemType::Enum,
                 };
                 inline::record_extern_fqn(cx, did, kind);
-                let path = external_path(cx, did, None, false, vec![], substs);
+                let path = external_path(cx, did, false, false, vec![], substs);
                 ResolvedPath { path, did, is_generic: false }
             }
             ty::Foreign(did) => {
                 inline::record_extern_fqn(cx, did, ItemType::ForeignType);
-                let path = external_path(cx, did, None, false, vec![], InternalSubsts::empty());
+                let path = external_path(cx, did, false, false, vec![], InternalSubsts::empty());
                 ResolvedPath { path, did, is_generic: false }
             }
             ty::Dynamic(ref obj, ref reg) => {
@@ -1477,7 +1471,7 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
 
                 for did in dids {
                     let empty = cx.tcx.intern_substs(&[]);
-                    let path = external_path(cx, did, Some(did), false, vec![], empty);
+                    let path = external_path(cx, did, true, false, vec![], empty);
                     inline::record_extern_fqn(cx, did, ItemType::Trait);
                     let bound = PolyTrait {
                         trait_: ResolvedPath { path, did, is_generic: false },
@@ -1494,7 +1488,7 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                     });
                 }
 
-                let path = external_path(cx, did, Some(did), false, bindings, substs);
+                let path = external_path(cx, did, true, false, bindings, substs);
                 bounds.insert(
                     0,
                     PolyTrait {

src/librustdoc/clean/types.rs

@@ -1158,7 +1158,7 @@ impl GenericBound {
     crate fn maybe_sized(cx: &mut DocContext<'_>) -> GenericBound {
         let did = cx.tcx.require_lang_item(LangItem::Sized, None);
         let empty = cx.tcx.intern_substs(&[]);
-        let path = external_path(cx, did, Some(did), false, vec![], empty);
+        let path = external_path(cx, did, true, false, vec![], empty);
         inline::record_extern_fqn(cx, did, ItemType::Trait);
         GenericBound::TraitBound(
             PolyTrait {

src/librustdoc/clean/utils.rs

@@ -93,7 +93,8 @@ crate fn krate(cx: &mut DocContext<'_>) -> Crate {
 
 fn external_generic_args(
     cx: &mut DocContext<'_>,
-    trait_did: Option<DefId>,
+    did: DefId,
+    is_trait: bool,
     has_self: bool,
     bindings: Vec<TypeBinding>,
     substs: SubstsRef<'_>,
@@ -121,32 +122,30 @@ fn external_generic_args(
         })
         .collect();
 
-    match trait_did {
-        // Attempt to sugar an external path like Fn<(A, B,), C> to Fn(A, B) -> C
-        Some(did) if cx.tcx.fn_trait_kind_from_lang_item(did).is_some() => {
-            assert!(ty_kind.is_some());
-            let inputs = match ty_kind {
-                Some(ty::Tuple(ref tys)) => tys.iter().map(|t| t.expect_ty().clean(cx)).collect(),
-                _ => return GenericArgs::AngleBracketed { args, bindings },
-            };
-            let output = None;
-            // FIXME(#20299) return type comes from a projection now
-            // match types[1].kind {
-            //     ty::Tuple(ref v) if v.is_empty() => None, // -> ()
-            //     _ => Some(types[1].clean(cx))
-            // };
-            GenericArgs::Parenthesized { inputs, output }
-        }
-        _ => GenericArgs::AngleBracketed { args, bindings },
+    if is_trait && cx.tcx.fn_trait_kind_from_lang_item(did).is_some() {
+        assert!(ty_kind.is_some());
+        let inputs = match ty_kind {
+            Some(ty::Tuple(ref tys)) => tys.iter().map(|t| t.expect_ty().clean(cx)).collect(),
+            _ => return GenericArgs::AngleBracketed { args, bindings },
+        };
+        let output = None;
+        // FIXME(#20299) return type comes from a projection now
+        // match types[1].kind {
+        //     ty::Tuple(ref v) if v.is_empty() => None, // -> ()
+        //     _ => Some(types[1].clean(cx))
+        // };
+        GenericArgs::Parenthesized { inputs, output }
+    } else {
+        GenericArgs::AngleBracketed { args, bindings }
     }
 }
 
-/// trait_did should be set to a trait's DefId if called on a TraitRef, in order to sugar
+/// `is_trait` should be set to `true` if called on a `TraitRef`, in order to sugar
 /// from `Fn<(A, B,), C>` to `Fn(A, B) -> C`
 pub(super) fn external_path(
     cx: &mut DocContext<'_>,
     did: DefId,
-    trait_did: Option<DefId>,
+    is_trait: bool,
     has_self: bool,
     bindings: Vec<TypeBinding>,
     substs: SubstsRef<'_>,
@@ -158,7 +157,7 @@ pub(super) fn external_path(
         res: Res::Def(def_kind, did),
         segments: vec![PathSegment {
             name,
-            args: external_generic_args(cx, trait_did, has_self, bindings, substs),
+            args: external_generic_args(cx, did, is_trait, has_self, bindings, substs),
         }],
     }
 }