From df25df1af84487b9ce9e793834e91bbf1485cecf Mon Sep 17 00:00:00 2001
From: EFanZh <efanzh@gmail.com>
Date: Sat, 27 Dec 2025 12:29:19 +0800
Subject: [PATCH] Constify `fmt::from_fn`

---
 library/core/src/fmt/builders.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/library/core/src/fmt/builders.rs b/library/core/src/fmt/builders.rs
index 197cddd3fa9d..7550dac45cd0 100644
--- a/library/core/src/fmt/builders.rs
+++ b/library/core/src/fmt/builders.rs
@@ -1227,8 +1227,9 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
 /// assert_eq!(format!("{:?}", wrapped), "'a'");
 /// ```
 #[stable(feature = "fmt_from_fn", since = "1.93.0")]
+#[rustc_const_stable(feature = "const_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> {
+pub const fn from_fn<F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result>(f: F) -> FromFn<F> {
     FromFn(f)
 }