@@ -207,8 +207,10 @@ pub fn attrs_to_doc_fragments<'a, A: AttributeExt + Clone + 'a>(
207207 attrs : impl Iterator < Item = ( & ' a A , Option < DefId > ) > ,
208208 doc_only : bool ,
209209) -> ( Vec < DocFragment > , ThinVec < A > ) {
210- let mut doc_fragments = Vec :: new ( ) ;
211- let mut other_attrs = ThinVec :: < A > :: new ( ) ;
210+ let ( min_size, max_size) = attrs. size_hint ( ) ;
211+ let size_hint = max_size. unwrap_or ( min_size) ;
212+ let mut doc_fragments = Vec :: with_capacity ( size_hint) ;
213+ let mut other_attrs = ThinVec :: < A > :: with_capacity ( if doc_only { 0 } else { size_hint } ) ;
212214 for ( attr, item_id) in attrs {
213215 if let Some ( ( doc_str, comment_kind) ) = attr. doc_str_and_comment_kind ( ) {
214216 let doc = beautify_doc_string ( doc_str, comment_kind) ;
@@ -230,6 +232,9 @@ pub fn attrs_to_doc_fragments<'a, A: AttributeExt + Clone + 'a>(
230232 }
231233 }
232234
235+ doc_fragments. shrink_to_fit ( ) ;
236+ other_attrs. shrink_to_fit ( ) ;
237+ 233238 unindent_doc_fragments ( & mut doc_fragments) ;
234239
235240 ( doc_fragments, other_attrs)
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