Remove support for specializing ToString outside the standard library

This is the only trait specializable outside of the standard library.
Before stabilizing specialization we will probably want to remove
support for this. It was originally made specializable to allow a more
efficient ToString in libproc_macro back when this way the only way to
get any data out of a TokenStream. We now support getting individual
tokens, so proc macros no longer need to call it as often.

1 files changed, 32 insertions, 37 deletions

diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index c5378d78d59..23d060d2158 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -2675,12 +2675,25 @@ pub trait ToString {
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: fmt::Display + ?Sized> ToString for T {
+    #[inline]
+    fn to_string(&self) -> String {
+        <Self as SpecToString>::spec_to_string(self)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+trait SpecToString {
+    fn spec_to_string(&self) -> String;
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<T: fmt::Display + ?Sized> SpecToString for T {
     // A common guideline is to not inline generic functions. However,
     // removing `#[inline]` from this method causes non-negligible regressions.
     // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
     // to try to remove it.
     #[inline]
-    default fn to_string(&self) -> String {
+    default fn spec_to_string(&self) -> String {
         let mut buf = String::new();
         let mut formatter =
             core::fmt::Formatter::new(&mut buf, core::fmt::FormattingOptions::new());
@@ -2691,42 +2704,34 @@ impl<T: fmt::Display + ?Sized> ToString for T {
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[unstable(feature = "ascii_char", issue = "110998")]
-impl ToString for core::ascii::Char {
+impl SpecToString for core::ascii::Char {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         self.as_str().to_owned()
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "char_to_string_specialization", since = "1.46.0")]
-impl ToString for char {
+impl SpecToString for char {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         String::from(self.encode_utf8(&mut [0; 4]))
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "bool_to_string_specialization", since = "1.68.0")]
-impl ToString for bool {
+impl SpecToString for bool {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         String::from(if *self { "true" } else { "false" })
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "u8_to_string_specialization", since = "1.54.0")]
-impl ToString for u8 {
+impl SpecToString for u8 {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         let mut buf = String::with_capacity(3);
         let mut n = *self;
         if n >= 10 {
@@ -2742,12 +2747,10 @@ impl ToString for u8 {
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "i8_to_string_specialization", since = "1.54.0")]
-impl ToString for i8 {
+impl SpecToString for i8 {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         let mut buf = String::with_capacity(4);
         if self.is_negative() {
             buf.push('-');
@@ -2788,11 +2791,9 @@ macro_rules! to_string_expr_wrap_in_deref {
 macro_rules! to_string_str {
     {$($($x:ident)*),+} => {
         $(
-            #[doc(hidden)]
-            #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
-            impl ToString for to_string_str_wrap_in_ref!($($x)*) {
+            impl SpecToString for to_string_str_wrap_in_ref!($($x)*) {
                 #[inline]
-                fn to_string(&self) -> String {
+                fn spec_to_string(&self) -> String {
                     String::from(to_string_expr_wrap_in_deref!(self ; $($x)*))
                 }
             }
@@ -2816,32 +2817,26 @@ to_string_str! {
     x,
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
-impl ToString for Cow<'_, str> {
+impl SpecToString for Cow<'_, str> {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         self[..].to_owned()
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "string_to_string_specialization", since = "1.17.0")]
-impl ToString for String {
+impl SpecToString for String {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         self.to_owned()
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "fmt_arguments_to_string_specialization", since = "1.71.0")]
-impl ToString for fmt::Arguments<'_> {
+impl SpecToString for fmt::Arguments<'_> {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         crate::fmt::format(*self)
     }
 }