Shifted to crate fmt from num

Author: madhav-madhusoodanan

library/core/src/fmt/int_format.rs

@@ -0,0 +1,24 @@
+use crate::mem::MaybeUninit;
+
+/// 41 is chosen as the buffer length, as it is larger
+/// than that required to accommodate i128::MIN
+/// (39 decimal digits, 1 for negative sign).
+const BUF_SIZE: usize = 41;
+
+/// A minimal buffer implementation containing elements of type
+/// `MaybeUninit<u8>`.
+#[unstable(feature = "int_format_into", issue = "138215")]
+#[derive(Debug)]
+pub struct NumBuffer {
+    /// An array of elements of type `MaybeUninit<u8>`.
+    pub contents: [MaybeUninit<u8>; BUF_SIZE],
+}
+
+#[unstable(feature = "int_format_into", issue = "138215")]
+impl NumBuffer {
+    /// Initializes `contents` as an uninitialized array of `MaybeUninit<u8>`.
+    #[unstable(feature = "int_format_into", issue = "138215")]
+    pub fn new() -> Self {
+        NumBuffer { contents: [MaybeUninit::<u8>::uninit(); BUF_SIZE] }
+    }
+}

library/core/src/fmt/mod.rs

@@ -12,6 +12,7 @@ use crate::{iter, mem, result, str};
 mod builders;
 #[cfg(not(no_fp_fmt_parse))]
 mod float;
+mod int_format;
 #[cfg(no_fp_fmt_parse)]
 mod nofloat;
 mod num;
@@ -46,6 +47,9 @@ impl From<rt::Alignment> for Option<Alignment> {
     }
 }
 
+#[unstable(feature = "int_format_into", issue = "138215")]
+pub use int_format::NumBuffer;
+
 #[stable(feature = "debug_builders", since = "1.2.0")]
 pub use self::builders::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
 #[unstable(feature = "debug_closure_helpers", issue = "117729")]