From ec1775d85d3e65945f5949f1b0e62cad37fe8e7a Mon Sep 17 00:00:00 2001
From: Markus Reiter <me@reitermark.us>
Date: Wed, 8 May 2024 21:51:50 +0200
Subject: [PATCH] Allow optimizing `u32::from::<char>`.

---
 library/core/src/char/convert.rs | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/library/core/src/char/convert.rs b/library/core/src/char/convert.rs
index f0c2636307fcf..5be203296360a 100644
--- a/library/core/src/char/convert.rs
+++ b/library/core/src/char/convert.rs
@@ -48,7 +48,12 @@ impl From<char> for u32 {
     /// ```
     #[inline]
     fn from(c: char) -> Self {
-        c as u32
+        let c = c as Self;
+
+        // SAFETY: `char::MAX` is the highest valid Unicode code point.
+        unsafe { core::hint::assert_unchecked(c <= char::MAX as Self) };
+
+        c
     }
 }
 
@@ -69,7 +74,12 @@ impl From<char> for u64 {
     fn from(c: char) -> Self {
         // The char is casted to the value of the code point, then zero-extended to 64 bit.
         // See [https://doc.rust-lang.org/reference/expressions/operator-expr.html#semantics]
-        c as u64
+        let c = c as Self;
+
+        // SAFETY: `char::MAX` is the highest valid Unicode code point.
+        unsafe { core::hint::assert_unchecked(c <= char::MAX as Self) };
+
+        c
     }
 }
 
@@ -90,7 +100,12 @@ impl From<char> for u128 {
     fn from(c: char) -> Self {
         // The char is casted to the value of the code point, then zero-extended to 128 bit.
         // See [https://doc.rust-lang.org/reference/expressions/operator-expr.html#semantics]
-        c as u128
+        let c = c as Self;
+
+        // SAFETY: `char::MAX` is the highest valid Unicode code point.
+        unsafe { core::hint::assert_unchecked(c <= char::MAX as Self) };
+
+        c
     }
 }