use drain_filter instead of filter and retain

Author: TaKO8Ki

compiler/rustc_resolve/src/diagnostics.rs

@@ -1708,10 +1708,7 @@ crate fn show_candidates(
 
     path_strings.sort();
     let core_path_strings =
-        path_strings.iter().filter(|p| p.starts_with("core::")).cloned().collect::<Vec<String>>();
-    if !core_path_strings.is_empty() {
-        path_strings.retain(|p| !p.starts_with("core::"));
-    }
+        path_strings.drain_filter(|p| p.starts_with("core::")).collect::<Vec<String>>();
     path_strings.extend(core_path_strings);
     path_strings.dedup();
 

compiler/rustc_resolve/src/lib.rs

@@ -10,6 +10,7 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(box_patterns)]
+#![feature(drain_filter)]
 #![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
 #![feature(format_args_capture)]