mir/borrowck: a few string tweaks

Author: ljedrz

src/librustc_mir/borrow_check/borrow_set.rs

@@ -92,12 +92,12 @@ impl<'tcx> fmt::Display for BorrowData<'tcx> {
             mir::BorrowKind::Mut { .. } => "mut ",
         };
         let region = self.region.to_string();
-        let region = if region.len() > 0 {
-            format!("{} ", region)
+        let separator = if !region.is_empty() {
+            " "
         } else {
-            region
+            ""
         };
-        write!(w, "&{}{}{:?}", region, kind, self.borrowed_place)
+        write!(w, "&{}{}{}{:?}", region, separator, kind, self.borrowed_place)
     }
 }
 

src/librustc_mir/borrow_check/error_reporting.rs

@@ -579,7 +579,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
     fn report_local_value_does_not_live_long_enough(
         &mut self,
         context: Context,
-        name: &String,
+        name: &str,
         scope_tree: &Lrc<ScopeTree>,
         borrow: &BorrowData<'tcx>,
         drop_span: Span,
@@ -1192,10 +1192,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             Place::Static(ref static_) => self.describe_field_from_ty(&static_.ty, field),
             Place::Projection(ref proj) => match proj.elem {
                 ProjectionElem::Deref => self.describe_field(&proj.base, field),
-                ProjectionElem::Downcast(def, variant_index) => format!(
-                    "{}",
-                    def.variants[variant_index].fields[field.index()].ident
-                ),
+                ProjectionElem::Downcast(def, variant_index) =>
+                    def.variants[variant_index].fields[field.index()].ident.to_string(),
                 ProjectionElem::Field(_, field_type) => {
                     self.describe_field_from_ty(&field_type, field)
                 }
@@ -1783,8 +1781,8 @@ impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
                 ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }),
                 _,
                 _,
-            ) => with_highlight_region_for_bound_region(*br, counter, || format!("{}", ty)),
-            _ => format!("{}", ty),
+            ) => with_highlight_region_for_bound_region(*br, counter, || ty.to_string()),
+            _ => ty.to_string(),
         }
     }
 
@@ -1795,9 +1793,9 @@ impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
             ty::TyKind::Ref(region, _, _) => match region {
                 ty::RegionKind::ReLateBound(_, br)
                 | ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }) => {
-                    with_highlight_region_for_bound_region(*br, counter, || format!("{}", region))
+                    with_highlight_region_for_bound_region(*br, counter, || region.to_string())
                 }
-                _ => format!("{}", region),
+                _ => region.to_string(),
             },
             _ => bug!("ty for annotation of borrow region is not a reference"),
         }

src/librustc_mir/borrow_check/move_errors.rs

@@ -331,7 +331,7 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                             _ => {
                                 let source = self.borrowed_content_source(place);
                                 self.infcx.tcx.cannot_move_out_of(
-                                    span, &format!("{}", source), origin
+                                    span, &source.to_string(), origin
                                 )
                             },
                         }
@@ -469,9 +469,9 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
             let binding_span = bind_to.source_info.span;
 
             if j == 0 {
-                err.span_label(binding_span, format!("data moved here"));
+                err.span_label(binding_span, "data moved here");
             } else {
-                err.span_label(binding_span, format!("...and here"));
+                err.span_label(binding_span, "...and here");
             }
 
             if binds_to.len() == 1 {

src/librustc_mir/borrow_check/mutability_errors.rs

@@ -504,7 +504,7 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                                 );
 
                                 let extra = if found {
-                                    String::from("")
+                                    String::new()
                                 } else {
                                     format!(", but it is not implemented for `{}`",
                                             substs.type_at(0))
@@ -583,7 +583,7 @@ fn suggest_ampmut<'cx, 'gcx, 'tcx>(
                 let ty = &src[ws_pos..];
                 return (assignment_rhs_span, format!("&{} mut {}", lt_name, ty));
             } else if src.starts_with('&') {
-                let borrowed_expr = src[1..].to_string();
+                let borrowed_expr = &src[1..];
                 return (assignment_rhs_span, format!("&mut {}", borrowed_expr));
             }
         }