nll: improve format operations

Author: ljedrz

src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs

@@ -87,9 +87,9 @@ impl<'tcx> BorrowExplanation<'tcx> {
                     // Otherwise, just report the whole type (and use
                     // the intentionally fuzzy phrase "destructor")
                     ty::Closure(..) =>
-                        ("destructor", format!("closure")),
+                        ("destructor", "closure".to_owned()),
                     ty::Generator(..) =>
-                        ("destructor", format!("generator")),
+                        ("destructor", "generator".to_owned()),
 
                     _ => ("destructor", format!("type `{}`", local_decl.ty)),
                 };

src/librustc_mir/borrow_check/nll/region_infer/dump_mir.rs

@@ -36,12 +36,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 let outlived_by = self.universal_region_relations.regions_outlived_by(region);
                 writeln!(
                     out,
-                    "| {r:rw$} | {c:cw$} | {ob}",
-                    r = format!("{:?}", region),
+                    "| {r:rw$?} | {c:cw$?} | {ob:?}",
+                    r = region,
                     rw = REGION_WIDTH,
-                    c = format!("{:?}", classification),
+                    c = classification,
                     cw = 8, // "External" at most
-                    ob = format!("{:?}", outlived_by)
+                    ob = outlived_by
                 )?;
             }
         }
@@ -51,8 +51,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         for region in self.regions() {
             writeln!(
                 out,
-                "| {r:rw$} | {ui:4?} | {v}",
-                r = format!("{:?}", region),
+                "| {r:rw$?} | {ui:4?} | {v}",
+                r = region,
                 rw = REGION_WIDTH,
                 ui = self.region_universe(region),
                 v = self.region_value_str(region),

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs

@@ -550,7 +550,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     let span = infcx.tcx.def_span(*did);
                     if let Ok(snippet) = infcx.tcx.sess.source_map().span_to_snippet(span) {
                         let suggestable_fr_name = if fr_name.was_named() {
-                            format!("{}", fr_name)
+                            fr_name.to_string()
                         } else {
                             "'_".to_string()
                         };