Remove unnecessary is_trait argument

It was only used for sugaring `Fn` trait bounds, and rustdoc already
checks that the `did` is for a `Fn` (or `FnMut`, `FnOnce`) lang item,
so it's not necessary to also check that the `did` belongs to a trait.

Author: camelid

Diff for: src/librustdoc/clean/mod.rs

@@ -164,8 +164,7 @@ 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, true, true, bounds.to_vec(), trait_ref.substs);
+        let path = external_path(cx, trait_ref.def_id, true, bounds.to_vec(), trait_ref.substs);
 
         debug!("ty::TraitRef\n  subst: {:?}\n", trait_ref.substs);
 
@@ -1442,12 +1441,12 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                     AdtKind::Enum => ItemType::Enum,
                 };
                 inline::record_extern_fqn(cx, did, kind);
-                let path = external_path(cx, did, false, false, vec![], substs);
+                let path = external_path(cx, did, 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, false, false, vec![], InternalSubsts::empty());
+                let path = external_path(cx, did, false, vec![], InternalSubsts::empty());
                 ResolvedPath { path, did, is_generic: false }
             }
             ty::Dynamic(ref obj, ref reg) => {
@@ -1471,7 +1470,7 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
 
                 for did in dids {
                     let empty = cx.tcx.intern_substs(&[]);
-                    let path = external_path(cx, did, true, false, vec![], empty);
+                    let path = external_path(cx, did, false, vec![], empty);
                     inline::record_extern_fqn(cx, did, ItemType::Trait);
                     let bound = PolyTrait {
                         trait_: ResolvedPath { path, did, is_generic: false },
@@ -1488,7 +1487,7 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                     });
                 }
 
-                let path = external_path(cx, did, true, false, bindings, substs);
+                let path = external_path(cx, did, false, bindings, substs);
                 bounds.insert(
                     0,
                     PolyTrait {

Diff for: 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, true, false, vec![], empty);
+        let path = external_path(cx, did, false, vec![], empty);
         inline::record_extern_fqn(cx, did, ItemType::Trait);
         GenericBound::TraitBound(
             PolyTrait {

Diff for: src/librustdoc/clean/utils.rs

@@ -94,7 +94,6 @@ crate fn krate(cx: &mut DocContext<'_>) -> Crate {
 fn external_generic_args(
     cx: &mut DocContext<'_>,
     did: DefId,
-    is_trait: bool,
     has_self: bool,
     bindings: Vec<TypeBinding>,
     substs: SubstsRef<'_>,
@@ -122,7 +121,7 @@ fn external_generic_args(
         })
         .collect();
 
-    if is_trait && cx.tcx.fn_trait_kind_from_lang_item(did).is_some() {
+    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(),
@@ -140,12 +139,9 @@ fn external_generic_args(
     }
 }
 
-/// `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,
-    is_trait: bool,
     has_self: bool,
     bindings: Vec<TypeBinding>,
     substs: SubstsRef<'_>,
@@ -157,7 +153,7 @@ pub(super) fn external_path(
         res: Res::Def(def_kind, did),
         segments: vec![PathSegment {
             name,
-            args: external_generic_args(cx, did, is_trait, has_self, bindings, substs),
+            args: external_generic_args(cx, did, has_self, bindings, substs),
         }],
     }
 }