Auto merge of #29615 - steveklabnik:lol_strings, r=alexcrichton

&format!("...") is the same as "" if we're not doing any interpolation,
and doesn't allocate an intermediate String.

Author: bors

src/librustc/middle/check_const.rs

@@ -225,7 +225,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
             {
                 self.tcx.sess.span_err(
                     expr.span,
-                    &format!("const fns are an unstable feature"));
+                    "const fns are an unstable feature");
                 fileline_help!(
                     self.tcx.sess,
                     expr.span,

src/librustc/middle/const_eval.rs

@@ -1232,7 +1232,7 @@ fn resolve_trait_associated_const<'a, 'tcx: 'a>(tcx: &'a ty::ctxt<'tcx>,
         _ => {
             tcx.sess.span_bug(
                 ti.span,
-                &format!("resolve_trait_associated_const: unexpected vtable type"))
+                "resolve_trait_associated_const: unexpected vtable type")
         }
     }
 }

src/librustc/middle/infer/error_reporting.rs

@@ -1751,7 +1751,7 @@ impl<'a, 'tcx> ErrorReportingHelpers<'tcx> for InferCtxt<'a, 'tcx> {
             infer::ParameterInScope(_, span) => {
                 self.tcx.sess.span_note(
                     span,
-                    &format!("...so that a type/lifetime parameter is in scope here"));
+                    "...so that a type/lifetime parameter is in scope here");
             }
             infer::DataBorrowed(ty, span) => {
                 self.tcx.sess.span_note(

src/librustc/middle/infer/mod.rs

@@ -1130,7 +1130,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         match self.tables.borrow().node_types.get(&ex.id) {
             Some(&t) => t,
             None => {
-                self.tcx.sess.bug(&format!("no type for expr in fcx"));
+                self.tcx.sess.bug("no type for expr in fcx");
             }
         }
     }

src/librustc/middle/traits/error_reporting.rs

@@ -498,7 +498,7 @@ fn note_obligation_cause_code<'a, 'tcx, T>(infcx: &InferCtxt<'a, 'tcx>,
         ObligationCauseCode::SliceOrArrayElem => {
             tcx.sess.fileline_note(
                 cause_span,
-                &format!("slice and array elements must have `Sized` type"));
+                "slice and array elements must have `Sized` type");
         }
         ObligationCauseCode::ProjectionWf(data) => {
             tcx.sess.fileline_note(

src/librustc/middle/ty/error.rs

@@ -288,10 +288,9 @@ impl<'tcx> ty::ctxt<'tcx> {
                 let found_str = values.found.sort_string(self);
                 if expected_str == found_str && expected_str == "closure" {
                     self.sess.span_note(sp,
-                        &format!("no two closures, even if identical, have the same type"));
+                        "no two closures, even if identical, have the same type");
                     self.sess.span_help(sp,
-                        &format!("consider boxing your closure and/or \
-                                  using it as a trait object"));
+                        "consider boxing your closure and/or using it as a trait object");
                 }
             },
             TyParamDefaultMismatch(values) => {
@@ -307,8 +306,7 @@ impl<'tcx> ty::ctxt<'tcx> {
                             .and_then(|node_id| self.map.opt_span(node_id))
                 {
                     Some(span) => {
-                        self.sess.span_note(span,
-                                            &format!("a default was defined here..."));
+                        self.sess.span_note(span, "a default was defined here...");
                     }
                     None => {
                         self.sess.note(
@@ -319,15 +317,14 @@ impl<'tcx> ty::ctxt<'tcx> {
 
                 self.sess.span_note(
                     expected.origin_span,
-                    &format!("...that was applied to an unconstrained type variable here"));
+                    "...that was applied to an unconstrained type variable here");
 
                 match
                     self.map.as_local_node_id(found.def_id)
                             .and_then(|node_id| self.map.opt_span(node_id))
                 {
                     Some(span) => {
-                        self.sess.span_note(span,
-                                            &format!("a second default was defined here..."));
+                        self.sess.span_note(span, "a second default was defined here...");
                     }
                     None => {
                         self.sess.note(
@@ -338,7 +335,7 @@ impl<'tcx> ty::ctxt<'tcx> {
 
                 self.sess.span_note(
                     found.origin_span,
-                    &format!("...that also applies to the same type variable here"));
+                    "...that also applies to the same type variable here");
             }
             _ => {}
         }

src/librustc_mir/build/expr/as_temp.rs

@@ -38,7 +38,7 @@ impl<'a,'tcx> Builder<'a,'tcx> {
         let temp_lifetime = match expr.temp_lifetime {
             Some(t) => t,
             None => {
-                this.hir.span_bug(expr.span, &format!("no temp_lifetime for expr"));
+                this.hir.span_bug(expr.span, "no temp_lifetime for expr");
             }
         };
         this.schedule_drop(expr.span, temp_lifetime, DropKind::Deep, &temp, expr_ty);

src/librustc_mir/hair/cx/expr.rs

@@ -236,7 +236,7 @@ impl<'tcx> Mirror<'tcx> for &'tcx hir::Expr {
                 let (adt_def, substs) = match range_ty.sty {
                     ty::TyStruct(adt_def, substs) => (adt_def, substs),
                     _ => {
-                        cx.tcx.sess.span_bug(self.span, &format!("unexpanded ast"));
+                        cx.tcx.sess.span_bug(self.span, "unexpanded ast");
                     }
                 };
 
@@ -555,14 +555,12 @@ fn convert_var<'a, 'tcx: 'a>(cx: &mut Cx<'a, 'tcx>,
                     match expr.node {
                         hir::ExprClosure(_, _, ref body) => body.id,
                         _ => {
-                            cx.tcx.sess.span_bug(expr.span,
-                                              &format!("closure expr is not a closure expr"));
+                            cx.tcx.sess.span_bug(expr.span, "closure expr is not a closure expr");
                         }
                     }
                 }
                 _ => {
-                    cx.tcx.sess.span_bug(expr.span,
-                                      &format!("ast-map has garbage for closure expr"));
+                    cx.tcx.sess.span_bug(expr.span, "ast-map has garbage for closure expr");
                 }
             };
 

src/librustc_mir/mir_map.rs

@@ -173,7 +173,7 @@ impl<'a, 'm, 'tcx> visit::Visitor<'tcx> for InnerDump<'a,'m,'tcx> {
                             None => {
                                 self.tcx.sess.span_err(
                                     item.span,
-                                    &format!("graphviz attribute requires a path"));
+                                    "graphviz attribute requires a path");
                             }
                         }
                     }

src/librustc_typeck/check/intrinsic.rs

@@ -458,14 +458,12 @@ fn match_intrinsic_type_to_type<'tcx, 'a>(
                     match_intrinsic_type_to_type(tcx, position, span, structural_to_nominal,
                                                  inner_expected, ty)
                 }
-                _ => simple_error(&format!("`{}`", t),
-                                  &format!("raw pointer")),
+                _ => simple_error(&format!("`{}`", t), "raw pointer"),
             }
         }
         Vector(ref inner_expected, ref _llvm_type, len) => {
             if !t.is_simd() {
-                simple_error(&format!("non-simd type `{}`", t),
-                             "simd type");
+                simple_error(&format!("non-simd type `{}`", t), "simd type");
                 return;
             }
             let t_len = t.simd_size(tcx);