review comments: avoid string modification

Author: estebank

Diff for: src/librustc_typeck/check/demand.rs

@@ -379,7 +379,19 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     }
                 };
                 if self.can_coerce(ref_ty, expected) {
-                    if let Ok(src) = cm.span_to_snippet(sp) {
+                    let mut sugg_sp = sp;
+                    if let hir::ExprKind::MethodCall(_segment, _sp, args) = &expr.node {
+                        let clone_path = "std::clone::Clone::clone";
+                        if let ([arg], Some(true)) = (&args[..], self.tables.borrow()
+                            .type_dependent_def_id(expr.hir_id)
+                            .map(|did| self.tcx.def_path_str(did).as_str() == clone_path))
+                        {
+                            // If this expression had a clone call when suggesting borrowing
+                            // we want to suggest removing it because it'd now be unecessary.
+                            sugg_sp = arg.span;
+                        }
+                    }
+                    if let Ok(src) = cm.span_to_snippet(sugg_sp) {
                         let needs_parens = match expr.node {
                             // parenthesize if needed (Issue #46756)
                             hir::ExprKind::Cast(_, _) |
@@ -426,28 +438,16 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             }
                         }
 
-                        let mut sugg = sugg_expr.as_str();
-                        if let hir::ExprKind::MethodCall(_segment, _sp, _args) = &expr.node {
-                            let clone_path = "std::clone::Clone::clone";
-                            if let Some(true) = self.tables.borrow()
-                                .type_dependent_def_id(expr.hir_id)
-                                .map(|did| self.tcx.def_path_str(did).as_str() == clone_path)
-                            {
-                                // If this expression had a clone call when suggesting borrowing
-                                // we want to suggest removing it because it'd now be unecessary.
-                                sugg = sugg_expr.trim_end_matches(".clone()");
-                            }
-                        }
                         return Some(match mutability {
                             hir::Mutability::MutMutable => (
                                 sp,
                                 "consider mutably borrowing here",
-                                format!("{}&mut {}", field_name, sugg),
+                                format!("{}&mut {}", field_name, sugg_expr),
                             ),
                             hir::Mutability::MutImmutable => (
                                 sp,
                                 "consider borrowing here",
-                                format!("{}&{}", field_name, sugg),
+                                format!("{}&{}", field_name, sugg_expr),
                             ),
                         });
                     }