collect diag suggestions instead of pushing into vector repeatedly

Author: yotamofek

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2680,19 +2680,16 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 return;
             }
 
-            let mut sugg = vec![];
             let sm = self.infcx.tcx.sess.source_map();
-
-            if let Some(span) = finder.closure_arg_span {
-                sugg.push((sm.next_point(span.shrink_to_lo()).shrink_to_hi(), finder.suggest_arg));
-            }
-            for span in finder.closure_change_spans {
-                sugg.push((span, "this".to_string()));
-            }
-
-            for (span, suggest) in finder.closure_call_changes {
-                sugg.push((span, suggest));
-            }
+            let sugg = finder
+                .closure_arg_span
+                .map(|span| (sm.next_point(span.shrink_to_lo()).shrink_to_hi(), finder.suggest_arg))
+                .into_iter()
+                .chain(
+                    finder.closure_change_spans.into_iter().map(|span| (span, "this".to_string())),
+                )
+                .chain(finder.closure_call_changes)
+                .collect();
 
             err.multipart_suggestion_verbose(
                 "try explicitly passing `&Self` into the closure as an argument",