Rollup merge of #100157 - rust-lang:notriddle/use-map-instead-of-repe…

…ated-push, r=Dylan-DPC

rustdoc: use `collect()` instead of repeatedly pushing

src/librustdoc/clean/mod.rs

@@ -1617,9 +1617,10 @@ pub(crate) fn clean_middle_ty<'tcx>(
             // HACK: pick the first `did` as the `did` of the trait object. Someone
             // might want to implement "native" support for marker-trait-only
             // trait objects.
-            let mut dids = obj.principal_def_id().into_iter().chain(obj.auto_traits());
-            let did = dids
-                .next()
+            let mut dids = obj.auto_traits();
+            let did = obj
+                .principal_def_id()
+                .or_else(|| dids.next())
                 .unwrap_or_else(|| panic!("found trait object `{:?}` with no traits?", this));
             let substs = match obj.principal() {
                 Some(principal) => principal.skip_binder().substs,
@@ -1630,19 +1631,18 @@ pub(crate) fn clean_middle_ty<'tcx>(
             inline::record_extern_fqn(cx, did, ItemType::Trait);
 
             let lifetime = clean_middle_region(*reg);
-            let mut bounds = vec![];
-
-            for did in dids {
-                let empty = cx.tcx.intern_substs(&[]);
-                let path = external_path(cx, did, false, vec![], empty);
-                inline::record_extern_fqn(cx, did, ItemType::Trait);
-                let bound = PolyTrait { trait_: path, generic_params: Vec::new() };
-                bounds.push(bound);
-            }
+            let mut bounds = dids
+                .map(|did| {
+                    let empty = cx.tcx.intern_substs(&[]);
+                    let path = external_path(cx, did, false, vec![], empty);
+                    inline::record_extern_fqn(cx, did, ItemType::Trait);
+                    PolyTrait { trait_: path, generic_params: Vec::new() }
+                })
+                .collect::<Vec<_>>();
 
-            let mut bindings = vec![];
-            for pb in obj.projection_bounds() {
-                bindings.push(TypeBinding {
+            let bindings = obj
+                .projection_bounds()
+                .map(|pb| TypeBinding {
                     assoc: projection_to_path_segment(
                         pb.skip_binder()
                             .lift_to_tcx(cx.tcx)
@@ -1656,8 +1656,8 @@ pub(crate) fn clean_middle_ty<'tcx>(
                     kind: TypeBindingKind::Equality {
                         term: clean_middle_term(pb.skip_binder().term, cx),
                     },
-                });
-            }
+                })
+                .collect();
 
             let path = external_path(cx, did, false, bindings, substs);
             bounds.insert(0, PolyTrait { trait_: path, generic_params: Vec::new() });