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)
```

3 files changed, 4 insertions, 4 deletions

diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index b84046d1050..9f8909e1626 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -380,7 +380,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                                             structs, enums and unions");
                         if let ast::AttrStyle::Inner = attr.style {
                             let trait_list = traits.iter()
-                                .map(|t| format!("{}", t)).collect::<Vec<_>>();
+                                .map(|t| t.to_string()).collect::<Vec<_>>();
                             let suggestion = format!("#[derive({})]", trait_list.join(", "));
                             err.span_suggestion_with_applicability(
                                 span, "try an outer attribute", suggestion,
@@ -558,7 +558,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         invoc.expansion_data.mark.set_expn_info(ExpnInfo {
             call_site: attr.span,
             def_site: None,
-            format: MacroAttribute(Symbol::intern(&format!("{}", attr.path))),
+            format: MacroAttribute(Symbol::intern(&attr.path.to_string())),
             allow_internal_unstable: false,
             allow_internal_unsafe: false,
             local_inner_macros: false,
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 56760546c50..9011b6e48b9 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -6320,7 +6320,7 @@ impl<'a> Parser<'a> {
                 mod_name: mod_name.clone(),
                 default_path: default_path_str,
                 secondary_path: secondary_path_str,
-                dir_path: format!("{}", dir_path.display()),
+                dir_path: dir_path.display().to_string(),
             }),
             (true, true) => Err(Error::DuplicatePaths {
                 mod_name: mod_name.clone(),
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 08c9ec4c989..54ce06f61ef 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -631,7 +631,7 @@ pub trait PrintState<'a> {
                         self.writer().word(&ut.val_to_string(i))
                     }
                     ast::LitIntType::Unsuffixed => {
-                        self.writer().word(&format!("{}", i))
+                        self.writer().word(&i.to_string())
                     }
                 }
             }