Rollup merge of #42134 - scottmcm:rangeinclusive-struct, r=aturon

Make RangeInclusive just a two-field struct

Not being an enum improves ergonomics and consistency, especially since NonEmpty variant wasn't prevented from being empty.  It can still be iterable without an extra "done" bit by making the range have !(start <= end), which is even possible without changing the Step trait.

Implements merged https://github.com/rust-lang/rfcs/pull/1980; tracking issue https://github.com/rust-lang/rust/issues/28237.

This is definitely a breaking change to anything consuming `RangeInclusive` directly (not as an Iterator) or constructing it without using the sugar.  Is there some change that would make sense before this so compilation failures could be compatibly fixed ahead of time?

r? @aturon (as FCP proposer on the RFC)

1 files changed, 27 insertions, 40 deletions

diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index 24ebfeb62e2..cef3682fd94 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -981,95 +981,82 @@ impl<T> SliceIndex<[T]> for ops::RangeInclusive<usize> {
 
     #[inline]
     fn get(self, slice: &[T]) -> Option<&[T]> {
-        match self {
-            ops::RangeInclusive::Empty { .. } => Some(&[]),
-            ops::RangeInclusive::NonEmpty { end, .. } if end == usize::max_value() => None,
-            ops::RangeInclusive::NonEmpty { start, end } => (start..end + 1).get(slice),
-        }
+        if self.end == usize::max_value() { None }
+        else { (self.start..self.end + 1).get(slice) }
     }
 
     #[inline]
     fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
-        match self {
-            ops::RangeInclusive::Empty { .. } => Some(&mut []),
-            ops::RangeInclusive::NonEmpty { end, .. } if end == usize::max_value() => None,
-            ops::RangeInclusive::NonEmpty { start, end } => (start..end + 1).get_mut(slice),
-        }
+        if self.end == usize::max_value() { None }
+        else { (self.start..self.end + 1).get_mut(slice) }
     }
 
     #[inline]
     unsafe fn get_unchecked(self, slice: &[T]) -> &[T] {
-        match self {
-            ops::RangeInclusive::Empty { .. } => &[],
-            ops::RangeInclusive::NonEmpty { start, end } => (start..end + 1).get_unchecked(slice),
-        }
+        (self.start..self.end + 1).get_unchecked(slice)
     }
 
     #[inline]
     unsafe fn get_unchecked_mut(self, slice: &mut [T]) -> &mut [T] {
-        match self {
-            ops::RangeInclusive::Empty { .. } => &mut [],
-            ops::RangeInclusive::NonEmpty { start, end } => {
-                (start..end + 1).get_unchecked_mut(slice)
-            }
-        }
+        (self.start..self.end + 1).get_unchecked_mut(slice)
     }
 
     #[inline]
     fn index(self, slice: &[T]) -> &[T] {
-        match self {
-            ops::RangeInclusive::Empty { .. } => &[],
-            ops::RangeInclusive::NonEmpty { end, .. } if end == usize::max_value() => {
-                panic!("attempted to index slice up to maximum usize");
-            },
-            ops::RangeInclusive::NonEmpty { start, end } => (start..end + 1).index(slice),
-        }
+        assert!(self.end != usize::max_value(),
+            "attempted to index slice up to maximum usize");
+        (self.start..self.end + 1).index(slice)
     }
 
     #[inline]
     fn index_mut(self, slice: &mut [T]) -> &mut [T] {
-        match self {
-            ops::RangeInclusive::Empty { .. } => &mut [],
-            ops::RangeInclusive::NonEmpty { end, .. } if end == usize::max_value() => {
-                panic!("attempted to index slice up to maximum usize");
-            },
-            ops::RangeInclusive::NonEmpty { start, end } => (start..end + 1).index_mut(slice),
-        }
+        assert!(self.end != usize::max_value(),
+            "attempted to index slice up to maximum usize");
+        (self.start..self.end + 1).index_mut(slice)
     }
 }
 
+#[cfg(stage0)] // The bootstrap compiler has a different `...` desugar
+fn inclusive(start: usize, end: usize) -> ops::RangeInclusive<usize> {
+    ops::RangeInclusive { start, end }
+}
+#[cfg(not(stage0))]
+fn inclusive(start: usize, end: usize) -> ops::RangeInclusive<usize> {
+    start...end
+}
+
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl<T> SliceIndex<[T]> for ops::RangeToInclusive<usize> {
     type Output = [T];
 
     #[inline]
     fn get(self, slice: &[T]) -> Option<&[T]> {
-        (0...self.end).get(slice)
+        inclusive(0, self.end).get(slice)
     }
 
     #[inline]
     fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
-        (0...self.end).get_mut(slice)
+        inclusive(0, self.end).get_mut(slice)
     }
 
     #[inline]
     unsafe fn get_unchecked(self, slice: &[T]) -> &[T] {
-        (0...self.end).get_unchecked(slice)
+        inclusive(0, self.end).get_unchecked(slice)
     }
 
     #[inline]
     unsafe fn get_unchecked_mut(self, slice: &mut [T]) -> &mut [T] {
-        (0...self.end).get_unchecked_mut(slice)
+        inclusive(0, self.end).get_unchecked_mut(slice)
     }
 
     #[inline]
     fn index(self, slice: &[T]) -> &[T] {
-        (0...self.end).index(slice)
+        inclusive(0, self.end).index(slice)
     }
 
     #[inline]
     fn index_mut(self, slice: &mut [T]) -> &mut [T] {
-        (0...self.end).index_mut(slice)
+        inclusive(0, self.end).index_mut(slice)
     }
 }