make item_struct and item_union return impl fmt::Display

Author: yotamofek

src/librustdoc/html/render/print_item.rs

@@ -243,8 +243,8 @@ pub(super) fn print_item(cx: &Context<'_>, item: &clean::Item, buf: &mut String)
             write_str(buf, format_args!("{}", item_function(cx, item, f)))
         }
         clean::TraitItem(ref t) => write_str(buf, format_args!("{}", item_trait(cx, item, t))),
-        clean::StructItem(ref s) => item_struct(buf, cx, item, s),
-        clean::UnionItem(ref s) => item_union(buf, cx, item, s),
+        clean::StructItem(ref s) => write_str(buf, format_args!("{}", item_struct(cx, item, s))),
+        clean::UnionItem(ref s) => write_str(buf, format_args!("{}", item_union(cx, item, s))),
         clean::EnumItem(ref e) => item_enum(buf, cx, item, e),
         clean::TypeAliasItem(ref t) => item_type_alias(buf, cx, item, t),
         clean::MacroItem(ref m) => item_macro(buf, cx, item, m),
@@ -1470,7 +1470,11 @@ fn item_type_alias(w: &mut String, cx: &Context<'_>, it: &clean::Item, t: &clean
     }
 }
 
-fn item_union(w: &mut String, cx: &Context<'_>, it: &clean::Item, s: &clean::Union) {
+fn item_union<'a, 'tcx>(
+    cx: &'a Context<'tcx>,
+    it: &'a clean::Item,
+    s: &'a clean::Union,
+) -> impl fmt::Display + 'a + Captures<'tcx> {
     item_template!(
         #[template(path = "item_union.html")]
         struct ItemUnion<'a, 'cx> {
@@ -1527,7 +1531,10 @@ fn item_union(w: &mut String, cx: &Context<'_>, it: &clean::Item, s: &clean::Uni
         }
     }
 
-    ItemUnion { cx, it, s }.render_into(w).unwrap();
+    fmt::from_fn(|w| {
+        ItemUnion { cx, it, s }.render_into(w).unwrap();
+        Ok(())
+    })
 }
 
 fn print_tuple_struct_fields<'a, 'cx: 'a>(
@@ -1981,30 +1988,32 @@ fn item_constant(
     write_str(w, format_args!("{}", document(cx, it, None, HeadingOffset::H2)));
 }
 
-fn item_struct(w: &mut String, cx: &Context<'_>, it: &clean::Item, s: &clean::Struct) {
-    wrap_item(w, |w| {
-        render_attributes_in_code(w, it, cx);
-        write_str(
-            w,
-            format_args!(
+fn item_struct<'a, 'tcx>(
+    cx: &'a Context<'tcx>,
+    it: &'a clean::Item,
+    s: &'a clean::Struct,
+) -> impl fmt::Display + 'a + Captures<'tcx> {
+    fmt::from_fn(|w| {
+        wrap_item(w, |w| {
+            render_attributes_in_code(w, it, cx);
+            write!(
+                w,
                 "{}",
                 render_struct(it, Some(&s.generics), s.ctor_kind, &s.fields, "", true, cx)
-            ),
-        );
-    });
+            )
+        })?;
 
-    let def_id = it.item_id.expect_def_id();
+        let def_id = it.item_id.expect_def_id();
 
-    write_str(
-        w,
-        format_args!(
+        write!(
+            w,
             "{}{}{}{}",
             document(cx, it, None, HeadingOffset::H2),
             item_fields(cx, it, &s.fields, s.ctor_kind),
             render_assoc_items(cx, it, def_id, AssocItemRender::All),
             document_type_layout(cx, def_id),
-        ),
-    );
+        )
+    })
 }
 
 fn item_fields<'a, 'tcx>(