Stabilize Range[Inclusive]::is_empty

I would like to propose these two simple methods for stabilization:
- Knowing that a range is exhaused isn't otherwise trivial
- Clippy would like to suggest them, but had to do extra work to disable that path <https://github.com/rust-lang/rust-clippy/issues/3807> because they're unstable
- These work on `PartialOrd`, consistently with now-stable `contains`, and are thus more general than iterator-based approaches that need `Step`
- They've been unchanged for some time, and have picked up uses in the compiler
- Stabilizing them doesn't block any future iterator-based is_empty plans, as the inherent ones are preferred in name resolution

library/core/src/ops/range.rs

@@ -125,8 +125,6 @@ impl<Idx: PartialOrd<Idx>> Range<Idx> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(range_is_empty)]
-    ///
     /// assert!(!(3..5).is_empty());
     /// assert!( (3..3).is_empty());
     /// assert!( (3..2).is_empty());
@@ -135,13 +133,11 @@ impl<Idx: PartialOrd<Idx>> Range<Idx> {
     /// The range is empty if either side is incomparable:
     ///
     /// ```
-    /// #![feature(range_is_empty)]
-    ///
     /// assert!(!(3.0..5.0).is_empty());
     /// assert!( (3.0..f32::NAN).is_empty());
     /// assert!( (f32::NAN..5.0).is_empty());
     /// ```
-    #[unstable(feature = "range_is_empty", reason = "recently added", issue = "48111")]
+    #[stable(feature = "range_is_empty", since = "1.47.0")]
     pub fn is_empty(&self) -> bool {
         !(self.start < self.end)
     }
@@ -481,8 +477,6 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(range_is_empty)]
-    ///
     /// assert!(!(3..=5).is_empty());
     /// assert!(!(3..=3).is_empty());
     /// assert!( (3..=2).is_empty());
@@ -491,8 +485,6 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// The range is empty if either side is incomparable:
     ///
     /// ```
-    /// #![feature(range_is_empty)]
-    ///
     /// assert!(!(3.0..=5.0).is_empty());
     /// assert!( (3.0..=f32::NAN).is_empty());
     /// assert!( (f32::NAN..=5.0).is_empty());
@@ -501,14 +493,12 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// This method returns `true` after iteration has finished:
     ///
     /// ```
-    /// #![feature(range_is_empty)]
-    ///
     /// let mut r = 3..=5;
     /// for _ in r.by_ref() {}
     /// // Precise field values are unspecified here
     /// assert!(r.is_empty());
     /// ```
-    #[unstable(feature = "range_is_empty", reason = "recently added", issue = "48111")]
+    #[stable(feature = "range_is_empty", since = "1.47.0")]
     #[inline]
     pub fn is_empty(&self) -> bool {
         self.exhausted || !(self.start <= self.end)

library/core/tests/lib.rs

@@ -17,7 +17,6 @@
 #![feature(try_find)]
 #![feature(is_sorted)]
 #![feature(pattern)]
-#![feature(range_is_empty)]
 #![feature(raw)]
 #![feature(sort_internals)]
 #![feature(slice_partition_at_index)]

src/librustc_infer/lib.rs

@@ -22,7 +22,6 @@
 #![feature(extend_one)]
 #![feature(never_type)]
 #![feature(or_patterns)]
-#![feature(range_is_empty)]
 #![feature(in_band_lifetimes)]
 #![feature(crate_visibility_modifier)]
 #![recursion_limit = "512"] // For rustdoc

src/librustc_middle/lib.rs

@@ -40,7 +40,6 @@
 #![feature(nll)]
 #![feature(option_expect_none)]
 #![feature(or_patterns)]
-#![feature(range_is_empty)]
 #![feature(min_specialization)]
 #![feature(trusted_len)]
 #![feature(stmt_expr_attributes)]

src/librustc_mir/lib.rs

@@ -22,7 +22,6 @@ Rust MIR: a lowered representation of Rust.
 #![feature(try_blocks)]
 #![feature(associated_type_bounds)]
 #![feature(associated_type_defaults)]
-#![feature(range_is_empty)]
 #![feature(stmt_expr_attributes)]
 #![feature(trait_alias)]
 #![feature(option_expect_none)]

src/test/ui/range_inclusive.rs

@@ -1,6 +1,5 @@
 // run-pass
 // Test inclusive range syntax.
-#![feature(range_is_empty)]
 #![allow(unused_braces)]
 #![allow(unused_comparisons)]