refactor(complete): Remove unused allocation

Author: epage

clap_complete/src/engine/complete.rs

@@ -559,13 +559,13 @@ fn populate_arg_candidate(candidate: CompletionCandidate, arg: &clap::Arg) -> Co
 }
 
 /// Get the possible values for completion
-fn possible_values(a: &clap::Arg) -> Option<Vec<clap::builder::PossibleValue>> {
+fn possible_values(
+    a: &clap::Arg,
+) -> Option<Box<dyn Iterator<Item = clap::builder::PossibleValue> + '_>> {
     if !a.get_num_args().expect("built").takes_values() {
         None
     } else {
-        a.get_value_parser()
-            .possible_values()
-            .map(|pvs| pvs.collect())
+        a.get_value_parser().possible_values()
     }
 }