Auto merge of #52767 - ljedrz:avoid_format, r=petrochenkov

Prefer to_string() to format!()

Simple benchmarks suggest in some cases it can be faster by even 37%:
```
test converting_f64_long  ... bench:         339 ns/iter (+/- 199)
test converting_f64_short ... bench:         136 ns/iter (+/- 34)
test converting_i32_long  ... bench:          87 ns/iter (+/- 16)
test converting_i32_short ... bench:          87 ns/iter (+/- 49)
test converting_str       ... bench:          54 ns/iter (+/- 15)
test formatting_f64_long  ... bench:         349 ns/iter (+/- 176)
test formatting_f64_short ... bench:         145 ns/iter (+/- 14)
test formatting_i32_long  ... bench:          98 ns/iter (+/- 14)
test formatting_i32_short ... bench:          93 ns/iter (+/- 15)
test formatting_str       ... bench:          86 ns/iter (+/- 23)
```

Author: bors

src/bootstrap/builder.rs

@@ -925,7 +925,7 @@ impl<'a> Builder<'a> {
             cargo.env("RUSTC_VERIFY_LLVM_IR", "1");
         }
 
-        cargo.env("RUSTC_VERBOSE", format!("{}", self.verbosity));
+        cargo.env("RUSTC_VERBOSE", self.verbosity.to_string());
 
         // in std, we want to avoid denying warnings for stage 0 as that makes cfg's painful.
         if self.config.deny_warnings && !(mode == Mode::Std && stage == 0) {

src/libcore/tests/str_lossy.rs

@@ -79,7 +79,7 @@ fn chunks() {
 fn display() {
     assert_eq!(
         "Hello\u{FFFD}\u{FFFD} There\u{FFFD} Goodbye",
-        &format!("{}", Utf8Lossy::from_bytes(b"Hello\xC0\x80 There\xE6\x83 Goodbye")));
+        &Utf8Lossy::from_bytes(b"Hello\xC0\x80 There\xE6\x83 Goodbye").to_string());
 }
 
 #[test]

src/librustc/infer/error_reporting/mod.rs

@@ -557,7 +557,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         // Output the lifetimes fot the first type
         let lifetimes = sub.regions()
             .map(|lifetime| {
-                let s = format!("{}", lifetime);
+                let s = lifetime.to_string();
                 if s.is_empty() {
                     "'_".to_string()
                 } else {
@@ -582,7 +582,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 value.0.extend((values.0).0);
                 other_value.0.extend((values.1).0);
             } else {
-                value.push_highlighted(format!("{}", type_arg));
+                value.push_highlighted(type_arg.to_string());
             }
 
             if len > 0 && i != len - 1 {
@@ -716,7 +716,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             mutbl: hir::Mutability,
             s: &mut DiagnosticStyledString,
         ) {
-            let r = &format!("{}", r);
+            let r = &r.to_string();
             s.push_highlighted(format!(
                 "&{}{}{}",
                 r,
@@ -727,7 +727,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     ""
                 }
             ));
-            s.push_normal(format!("{}", ty));
+            s.push_normal(ty.to_string());
         }
 
         match (&t1.sty, &t2.sty) {
@@ -768,7 +768,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     }
 
                     fn lifetime_display(lifetime: Region) -> String {
-                        let s = format!("{}", lifetime);
+                        let s = lifetime.to_string();
                         if s.is_empty() {
                             "'_".to_string()
                         } else {
@@ -863,8 +863,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     // We couldn't find anything in common, highlight everything.
                     //     let x: Bar<Qux> = y::<Foo<Zar>>();
                     (
-                        DiagnosticStyledString::highlighted(format!("{}", t1)),
-                        DiagnosticStyledString::highlighted(format!("{}", t2)),
+                        DiagnosticStyledString::highlighted(t1.to_string()),
+                        DiagnosticStyledString::highlighted(t2.to_string()),
                     )
                 }
             }
@@ -873,12 +873,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             (&ty::TyRef(r1, ref_ty1, mutbl1), _) if equals(&ref_ty1, &t2) => {
                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
                 push_ty_ref(&r1, ref_ty1, mutbl1, &mut values.0);
-                values.1.push_normal(format!("{}", t2));
+                values.1.push_normal(t2.to_string());
                 values
             }
             (_, &ty::TyRef(r2, ref_ty2, mutbl2)) if equals(&t1, &ref_ty2) => {
                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
-                values.0.push_normal(format!("{}", t1));
+                values.0.push_normal(t1.to_string());
                 push_ty_ref(&r2, ref_ty2, mutbl2, &mut values.1);
                 values
             }
@@ -902,8 +902,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 } else {
                     // We couldn't find anything in common, highlight everything.
                     (
-                        DiagnosticStyledString::highlighted(format!("{}", t1)),
-                        DiagnosticStyledString::highlighted(format!("{}", t2)),
+                        DiagnosticStyledString::highlighted(t1.to_string()),
+                        DiagnosticStyledString::highlighted(t2.to_string()),
                     )
                 }
             }
@@ -1073,8 +1073,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         }
 
         Some((
-            DiagnosticStyledString::highlighted(format!("{}", exp_found.expected)),
-            DiagnosticStyledString::highlighted(format!("{}", exp_found.found)),
+            DiagnosticStyledString::highlighted(exp_found.expected.to_string()),
+            DiagnosticStyledString::highlighted(exp_found.found.to_string()),
         ))
     }
 

src/librustc/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -57,7 +57,7 @@ impl<'a, 'gcx, 'tcx> NiceRegionError<'a, 'gcx, 'tcx> {
                         let lifetime_name = match sup_r {
                             RegionKind::ReFree(FreeRegion {
                                 bound_region: BoundRegion::BrNamed(_, ref name), ..
-                            }) => format!("{}", name),
+                            }) => name.to_string(),
                             _ => "'_".to_owned(),
                         };
                         if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(return_sp) {

src/librustc/mir/mod.rs

@@ -2093,7 +2093,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
 
                 // When printing regions, add trailing space if necessary.
                 let region = if ppaux::verbose() || ppaux::identify_regions() {
-                    let mut region = format!("{}", region);
+                    let mut region = region.to_string();
                     if region.len() > 0 {
                         region.push(' ');
                     }

src/librustc/session/code_stats.rs

@@ -135,8 +135,8 @@ impl CodeStats {
                 let VariantInfo { ref name, kind: _, align: _, size, ref fields } = *variant_info;
                 let indent = if !struct_like {
                     let name = match name.as_ref() {
-                        Some(name) => format!("{}", name),
-                        None => format!("{}", i),
+                        Some(name) => name.to_owned(),
+                        None => i.to_string(),
                     };
                     println!("print-type-size {}variant `{}`: {} bytes",
                              indent, name, size - discr_size);

src/librustc/traits/error_reporting.rs

@@ -543,7 +543,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     &data.parent_trait_ref);
                 match self.get_parent_trait_ref(&data.parent_code) {
                     Some(t) => Some(t),
-                    None => Some(format!("{}", parent_trait_ref.skip_binder().self_ty())),
+                    None => Some(parent_trait_ref.skip_binder().self_ty().to_string()),
                 }
             }
             _ => None,
@@ -797,12 +797,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                             ty::TypeVariants::TyTuple(ref tys) => ArgKind::Tuple(
                                 Some(span),
                                 tys.iter()
-                                    .map(|ty| ("_".to_owned(), format!("{}", ty.sty)))
+                                    .map(|ty| ("_".to_owned(), ty.sty.to_string()))
                                     .collect::<Vec<_>>()
                             ),
-                            _ => ArgKind::Arg("_".to_owned(), format!("{}", t.sty)),
+                            _ => ArgKind::Arg("_".to_owned(), t.sty.to_string()),
                         }).collect(),
-                    ref sty => vec![ArgKind::Arg("_".to_owned(), format!("{}", sty))],
+                    ref sty => vec![ArgKind::Arg("_".to_owned(), sty.to_string())],
                 };
                 if found.len() == expected.len() {
                     self.report_closure_arg_mismatch(span,
@@ -989,7 +989,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             }) => {
                 (self.tcx.sess.codemap().def_span(span),
                  fields.iter().map(|field| {
-                     ArgKind::Arg(format!("{}", field.ident), "_".to_string())
+                     ArgKind::Arg(field.ident.to_string(), "_".to_string())
                  }).collect::<Vec<_>>())
             }
             hir::map::NodeStructCtor(ref variant_data) => {
@@ -1152,7 +1152,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     ::rustc_target::spec::abi::Abi::Rust
                 )
             };
-            format!("{}", ty::Binder::bind(sig))
+            ty::Binder::bind(sig).to_string()
         }
 
         let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
@@ -1575,10 +1575,10 @@ impl ArgKind {
             ty::TyTuple(ref tys) => ArgKind::Tuple(
                 None,
                 tys.iter()
-                   .map(|ty| ("_".to_owned(), format!("{}", ty.sty)))
+                   .map(|ty| ("_".to_owned(), ty.sty.to_string()))
                    .collect::<Vec<_>>()
             ),
-            _ => ArgKind::Arg("_".to_owned(), format!("{}", t.sty)),
+            _ => ArgKind::Arg("_".to_owned(), t.sty.to_string()),
         }
     }
 }

src/librustc/ty/item_path.rs

@@ -315,7 +315,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             ty::TyUint(_) |
             ty::TyFloat(_) |
             ty::TyStr => {
-                buffer.push(&format!("{}", self_ty));
+                buffer.push(&self_ty.to_string());
             }
 
             _ => {

src/librustc/ty/mod.rs

@@ -225,7 +225,7 @@ impl AssociatedItem {
                 // late-bound regions, and we don't want method signatures to show up
                 // `as for<'r> fn(&'r MyType)`.  Pretty-printing handles late-bound
                 // regions just fine, showing `fn(&MyType)`.
-                format!("{}", tcx.fn_sig(self.def_id).skip_binder())
+                tcx.fn_sig(self.def_id).skip_binder().to_string()
             }
             ty::AssociatedKind::Type => format!("type {};", self.ident),
             ty::AssociatedKind::Existential => format!("existential type {};", self.ident),

src/librustc/util/common.rs

@@ -242,7 +242,7 @@ pub fn to_readable_str(mut val: usize) -> String {
         val /= 1000;
 
         if val == 0 {
-            groups.push(format!("{}", group));
+            groups.push(group.to_string());
             break;
         } else {
             groups.push(format!("{:03}", group));