From b570ebd37eb81fd8dff1b2e4651609d766043597 Mon Sep 17 00:00:00 2001
From: "Tim (Theemathas Chirananthavat)" <theemathas@gmail.com>
Date: Sat, 4 Jul 2026 17:54:11 +0700
Subject: [PATCH 1/2] Weaken guarantee for `From<legacy::RangeInclusive> for
 RangeInclusive`

As per https://github.com/rust-lang/rust/pull/155114#issuecomment-4845403701,
this `From` impl no longer guarantees panicking for exhausted iterators.
Instead, it only guarantees that the conversion will either panic or
produce an empty range.

This is done so that we can optimize the implementation of
`legacy::RangeInclusive` in a way such that we cannot check if it has
been exhausted in a generic context without a `Step` and/or `PartialOrd`
bound.
---
 library/core/src/range.rs | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/library/core/src/range.rs b/library/core/src/range.rs
index fb7a51a779f6d..74d1cfde034eb 100644
--- a/library/core/src/range.rs
+++ b/library/core/src/range.rs
@@ -402,7 +402,8 @@ const impl<T> From<legacy::RangeInclusive<T>> for RangeInclusive<T> {
     ///
     /// # Panics
     ///
-    /// Panics if the legacy range iterator has been exhausted.
+    /// If the legacy range iterator has been exhausted,
+    /// this function will either panic or return an empty range.
     ///
     /// # Examples
     ///
@@ -419,19 +420,16 @@ const impl<T> From<legacy::RangeInclusive<T>> for RangeInclusive<T> {
     /// assert_eq!((empty.start, empty.last), (0, 0));
     /// ```
     ///
-    /// ```should_panic
+    /// ```
     /// use core::range::legacy;
     /// use core::range::RangeInclusive;
+    /// use std::panic::catch_unwind;
     ///
     /// let mut exhausted: legacy::RangeInclusive<i32> = 0..=0;
     /// exhausted.next();
-    /// # if exhausted.is_empty() {
-    /// # // assert!s don't work correctly in `should_panic` doctests since you
-    /// # // can't assert the panic message. Skip the rest of the test instead,
-    /// # // so that the expected panic doesn't happen and the test fails.
-    /// assert!(exhausted.is_empty());
-    /// let _ = RangeInclusive::from(exhausted); // this panics
-    /// # }
+    /// let result = catch_unwind(|| RangeInclusive::from(exhausted));
+    /// // The `from` call either panicked or returned an empty range.
+    /// assert!(result.is_err() || result.is_ok_and(|range| range.is_empty()));
     /// ```
     #[inline]
     fn from(value: legacy::RangeInclusive<T>) -> Self {

From 1920371ad120c8c23e0254e04086d448ef46a2ee Mon Sep 17 00:00:00 2001
From: "Tim (Theemathas Chirananthavat)" <theemathas@gmail.com>
Date: Sun, 5 Jul 2026 22:55:53 +0700
Subject: [PATCH 2/2] Disable `RangeInclusive`'s `From` test when unwinding
 isn't available.

---
 library/core/src/range.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/library/core/src/range.rs b/library/core/src/range.rs
index 74d1cfde034eb..07f423edcfea1 100644
--- a/library/core/src/range.rs
+++ b/library/core/src/range.rs
@@ -421,6 +421,10 @@ const impl<T> From<legacy::RangeInclusive<T>> for RangeInclusive<T> {
     /// ```
     ///
     /// ```
+    /// # // This test requires unwinding to work.
+    /// # // Disable it when unwinding isn't available.
+    /// # #[cfg(panic = "unwind")]
+    /// # fn main() {
     /// use core::range::legacy;
     /// use core::range::RangeInclusive;
     /// use std::panic::catch_unwind;
@@ -430,6 +434,9 @@ const impl<T> From<legacy::RangeInclusive<T>> for RangeInclusive<T> {
     /// let result = catch_unwind(|| RangeInclusive::from(exhausted));
     /// // The `from` call either panicked or returned an empty range.
     /// assert!(result.is_err() || result.is_ok_and(|range| range.is_empty()));
+    /// # }
+    /// # #[cfg(not(panic = "unwind"))]
+    /// # fn main() {}
     /// ```
     #[inline]
     fn from(value: legacy::RangeInclusive<T>) -> Self {