2 files changed, 44 insertions, 36 deletions

diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
index 580f95eddce..4f7f8a5b84d 100644
--- a/library/core/src/fmt/mod.rs
+++ b/library/core/src/fmt/mod.rs
@@ -622,44 +622,9 @@ pub struct Arguments<'a> {
     args: &'a [rt::Argument<'a>],
 }
 
-/// Used by the format_args!() macro to create a fmt::Arguments object.
 #[doc(hidden)]
 #[unstable(feature = "fmt_internals", issue = "none")]
 impl<'a> Arguments<'a> {
-    #[inline]
-    pub const fn new_const<const N: usize>(pieces: &'a [&'static str; N]) -> Self {
-        const { assert!(N <= 1) };
-        Arguments { pieces, fmt: None, args: &[] }
-    }
-
-    /// When using the format_args!() macro, this function is used to generate the
-    /// Arguments structure.
-    #[inline]
-    pub const fn new_v1<const P: usize, const A: usize>(
-        pieces: &'a [&'static str; P],
-        args: &'a [rt::Argument<'a>; A],
-    ) -> Arguments<'a> {
-        const { assert!(P >= A && P <= A + 1, "invalid args") }
-        Arguments { pieces, fmt: None, args }
-    }
-
-    /// Specifies nonstandard formatting parameters.
-    ///
-    /// An `rt::UnsafeArg` is required because the following invariants must be held
-    /// in order for this function to be safe:
-    /// 1. The `pieces` slice must be at least as long as `fmt`.
-    /// 2. Every `rt::Placeholder::position` value within `fmt` must be a valid index of `args`.
-    /// 3. Every `rt::Count::Param` within `fmt` must contain a valid index of `args`.
-    #[inline]
-    pub const fn new_v1_formatted(
-        pieces: &'a [&'static str],
-        args: &'a [rt::Argument<'a>],
-        fmt: &'a [rt::Placeholder],
-        _unsafe_arg: rt::UnsafeArg,
-    ) -> Arguments<'a> {
-        Arguments { pieces, fmt: Some(fmt), args }
-    }
-
     /// Estimates the length of the formatted text.
     ///
     /// This is intended to be used for setting initial `String` capacity
diff --git a/library/core/src/fmt/rt.rs b/library/core/src/fmt/rt.rs
index e409771362e..ec5015e06d2 100644
--- a/library/core/src/fmt/rt.rs
+++ b/library/core/src/fmt/rt.rs
@@ -1,7 +1,10 @@
 #![allow(missing_debug_implementations)]
 #![unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
 
-//! These are the lang items used by format_args!().
+//! All types and methods in this file are used by the compiler in
+//! the expansion/lowering of format_args!().
+//!
+//! Do not modify them without understanding the consequences for the format_args!() macro.
 
 use super::*;
 use crate::hint::unreachable_unchecked;
@@ -229,3 +232,43 @@ impl UnsafeArg {
         Self { _private: () }
     }
 }
+
+/// Used by the format_args!() macro to create a fmt::Arguments object.
+#[doc(hidden)]
+#[unstable(feature = "fmt_internals", issue = "none")]
+#[rustc_diagnostic_item = "FmtArgumentsNew"]
+impl<'a> Arguments<'a> {
+    #[inline]
+    pub const fn new_const<const N: usize>(pieces: &'a [&'static str; N]) -> Self {
+        const { assert!(N <= 1) };
+        Arguments { pieces, fmt: None, args: &[] }
+    }
+
+    /// When using the format_args!() macro, this function is used to generate the
+    /// Arguments structure.
+    #[inline]
+    pub const fn new_v1<const P: usize, const A: usize>(
+        pieces: &'a [&'static str; P],
+        args: &'a [rt::Argument<'a>; A],
+    ) -> Arguments<'a> {
+        const { assert!(P >= A && P <= A + 1, "invalid args") }
+        Arguments { pieces, fmt: None, args }
+    }
+
+    /// Specifies nonstandard formatting parameters.
+    ///
+    /// An `rt::UnsafeArg` is required because the following invariants must be held
+    /// in order for this function to be safe:
+    /// 1. The `pieces` slice must be at least as long as `fmt`.
+    /// 2. Every `rt::Placeholder::position` value within `fmt` must be a valid index of `args`.
+    /// 3. Every `rt::Count::Param` within `fmt` must contain a valid index of `args`.
+    #[inline]
+    pub const fn new_v1_formatted(
+        pieces: &'a [&'static str],
+        args: &'a [rt::Argument<'a>],
+        fmt: &'a [rt::Placeholder],
+        _unsafe_arg: rt::UnsafeArg,
+    ) -> Arguments<'a> {
+        Arguments { pieces, fmt: Some(fmt), args }
+    }
+}