Rollup merge of rust-lang#145915 - coolreader18:stabilize-fmt_from_fn, r=dtolnay

Stabilize `fmt::from_fn`

Resolves rust-lang#146705, pending its FCP.

As discussed in that tracking issue and rust-lang#117729, this splits `fmt::from_fn` out from the `debug_closure_helpers` feature.

Author: Zalathar

alloc/src/fmt.rs

@@ -602,7 +602,7 @@ pub use core::fmt::{DebugAsHex, FormattingOptions, Sign};
 pub use core::fmt::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::{Formatter, Result, Write};
-#[unstable(feature = "debug_closure_helpers", issue = "117729")]
+#[stable(feature = "fmt_from_fn", since = "CURRENT_RUSTC_VERSION")]
 pub use core::fmt::{FromFn, from_fn};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::{LowerExp, UpperExp};

core/src/fmt/builders.rs

@@ -1210,13 +1210,12 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     }
 }
 
-/// Creates a type whose [`fmt::Debug`] and [`fmt::Display`] impls are provided with the function
-/// `f`.
+/// Creates a type whose [`fmt::Debug`] and [`fmt::Display`] impls are
+/// forwarded to the provided closure.
 ///
 /// # Examples
 ///
 /// ```
-/// #![feature(debug_closure_helpers)]
 /// use std::fmt;
 ///
 /// let value = 'a';
@@ -1227,21 +1226,19 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
 /// assert_eq!(format!("{}", wrapped), "'a'");
 /// assert_eq!(format!("{:?}", wrapped), "'a'");
 /// ```
-#[unstable(feature = "debug_closure_helpers", issue = "117729")]
+#[stable(feature = "fmt_from_fn", since = "CURRENT_RUSTC_VERSION")]
 #[must_use = "returns a type implementing Debug and Display, which do not have any effects unless they are used"]
 pub fn from_fn<F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result>(f: F) -> FromFn<F> {
     FromFn(f)
 }
 
-/// Implements [`fmt::Debug`] and [`fmt::Display`] using a function.
+/// Implements [`fmt::Debug`] and [`fmt::Display`] via the provided closure.
 ///
 /// Created with [`from_fn`].
-#[unstable(feature = "debug_closure_helpers", issue = "117729")]
-pub struct FromFn<F>(F)
-where
-    F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result;
+#[stable(feature = "fmt_from_fn", since = "CURRENT_RUSTC_VERSION")]
+pub struct FromFn<F>(F);
 
-#[unstable(feature = "debug_closure_helpers", issue = "117729")]
+#[stable(feature = "fmt_from_fn", since = "CURRENT_RUSTC_VERSION")]
 impl<F> fmt::Debug for FromFn<F>
 where
     F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result,
@@ -1251,7 +1248,7 @@ where
     }
 }
 
-#[unstable(feature = "debug_closure_helpers", issue = "117729")]
+#[stable(feature = "fmt_from_fn", since = "CURRENT_RUSTC_VERSION")]
 impl<F> fmt::Display for FromFn<F>
 where
     F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result,

core/src/fmt/mod.rs

@@ -39,7 +39,7 @@ pub use num_buffer::{NumBuffer, NumBufferTrait};
 
 #[stable(feature = "debug_builders", since = "1.2.0")]
 pub use self::builders::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
-#[unstable(feature = "debug_closure_helpers", issue = "117729")]
+#[stable(feature = "fmt_from_fn", since = "CURRENT_RUSTC_VERSION")]
 pub use self::builders::{FromFn, from_fn};
 
 /// The type returned by formatter methods.