A much simpler version of write

Author: nyurik

library/core/src/fmt/mod.rs

@@ -201,22 +201,14 @@ pub trait Write {
         impl<W: Write + ?Sized> SpecWriteFmt for &mut W {
             #[inline]
             default fn spec_write_fmt(mut self, args: Arguments<'_>) -> Result {
-                if let Some(s) = args.as_const_str() {
-                    self.write_str(s)
-                } else {
-                    write(&mut self, args)
-                }
+                write(&mut self, args)
             }
         }
 
         impl<W: Write> SpecWriteFmt for &mut W {
             #[inline]
             fn spec_write_fmt(self, args: Arguments<'_>) -> Result {
-                if let Some(s) = args.as_const_str() {
-                    self.write_str(s)
-                } else {
-                    write(self, args)
-                }
+                write(self, args)
             }
         }
 
@@ -438,15 +430,6 @@ impl<'a> Arguments<'a> {
             _ => None,
         }
     }
-
-    /// Same as [`Arguments::as_str`], but will only return `Some(s)` if it can be determined at compile time.
-    #[must_use]
-    #[inline]
-    fn as_const_str(&self) -> Option<&'static str> {
-        let s = self.as_str();
-        // SAFETY: both cases are valid as the result
-        if unsafe { core::intrinsics::is_val_statically_known(s.is_some()) } { s } else { None }
-    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1119,8 +1102,14 @@ pub trait UpperExp {
 /// ```
 ///
 /// [`write!`]: crate::write!
+#[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
+    if let Some(s) = args.as_str() { output.write_str(s) } else { write_internal(output, args) }
+}
+
+/// Actual implementation of the [`write`], but without the simple string optimization.
+fn write_internal(output: &mut dyn Write, args: Arguments<'_>) -> Result {
     let mut formatter = Formatter::new(output);
     let mut idx = 0;
 
@@ -1599,9 +1588,8 @@ impl<'a> Formatter<'a> {
     /// assert_eq!(format!("{:0>8}", Foo(2)), "Foo 2");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[inline]
     pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
-        if let Some(s) = fmt.as_const_str() { self.buf.write_str(s) } else { write(self.buf, fmt) }
+        write(self.buf, fmt)
     }
 
     /// Flags for formatting
@@ -2290,13 +2278,8 @@ impl Write for Formatter<'_> {
         self.buf.write_char(c)
     }
 
-    #[inline]
     fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
-        if let Some(s) = args.as_const_str() {
-            self.buf.write_str(s)
-        } else {
-            write(self.buf, args)
-        }
+        write(self.buf, args)
     }
 }
 

library/core/src/lib.rs

@@ -176,7 +176,6 @@
 #![feature(ip)]
 #![feature(ip_bits)]
 #![feature(is_ascii_octdigit)]
-#![feature(is_val_statically_known)]
 #![feature(isqrt)]
 #![feature(maybe_uninit_uninit_array)]
 #![feature(non_null_convenience)]