From 162fb713ac66fef8f6a1d14bae9d1d4b35f76411 Mon Sep 17 00:00:00 2001
From: Jason Newcomb <jsnewcomb@pm.me>
Date: Fri, 21 Feb 2025 16:01:19 -0500
Subject: Allow SliceIndex to be indexed by ranges.

---
 compiler/rustc_index/src/idx.rs   | 91 +++++++++++++++++++++++++++++++++++++++
 compiler/rustc_index/src/lib.rs   |  3 +-
 compiler/rustc_index/src/slice.rs | 33 ++++++++------
 3 files changed, 113 insertions(+), 14 deletions(-)

(limited to 'compiler/rustc_index')

diff --git a/compiler/rustc_index/src/idx.rs b/compiler/rustc_index/src/idx.rs
index b85160540d8..33f406e2113 100644
--- a/compiler/rustc_index/src/idx.rs
+++ b/compiler/rustc_index/src/idx.rs
@@ -1,5 +1,7 @@
 use std::fmt::Debug;
 use std::hash::Hash;
+use std::ops;
+use std::slice::SliceIndex;
 
 /// Represents some newtyped `usize` wrapper.
 ///
@@ -43,3 +45,92 @@ impl Idx for u32 {
         self as usize
     }
 }
+
+/// Helper trait for indexing operations with a custom index type.
+pub trait IntoSliceIdx<I, T: ?Sized> {
+    type Output: SliceIndex<T>;
+    fn into_slice_idx(self) -> Self::Output;
+}
+
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for I {
+    type Output = usize;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        self.index()
+    }
+}
+
+impl<I, T> IntoSliceIdx<I, [T]> for ops::RangeFull {
+    type Output = ops::RangeFull;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        self
+    }
+}
+
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for ops::Range<I> {
+    type Output = ops::Range<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        ops::Range { start: self.start.index(), end: self.end.index() }
+    }
+}
+
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for ops::RangeFrom<I> {
+    type Output = ops::RangeFrom<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        ops::RangeFrom { start: self.start.index() }
+    }
+}
+
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for ops::RangeTo<I> {
+    type Output = ops::RangeTo<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        ..self.end.index()
+    }
+}
+
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for ops::RangeInclusive<I> {
+    type Output = ops::RangeInclusive<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        ops::RangeInclusive::new(self.start().index(), self.end().index())
+    }
+}
+
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for ops::RangeToInclusive<I> {
+    type Output = ops::RangeToInclusive<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        ..=self.end.index()
+    }
+}
+
+#[cfg(feature = "nightly")]
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for core::range::Range<I> {
+    type Output = core::range::Range<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        core::range::Range { start: self.start.index(), end: self.end.index() }
+    }
+}
+
+#[cfg(feature = "nightly")]
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for core::range::RangeFrom<I> {
+    type Output = core::range::RangeFrom<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        core::range::RangeFrom { start: self.start.index() }
+    }
+}
+
+#[cfg(feature = "nightly")]
+impl<I: Idx, T> IntoSliceIdx<I, [T]> for core::range::RangeInclusive<I> {
+    type Output = core::range::RangeInclusive<usize>;
+    #[inline]
+    fn into_slice_idx(self) -> Self::Output {
+        core::range::RangeInclusive { start: self.start.index(), end: self.end.index() }
+    }
+}
diff --git a/compiler/rustc_index/src/lib.rs b/compiler/rustc_index/src/lib.rs
index cae55230b06..3441a5f65c7 100644
--- a/compiler/rustc_index/src/lib.rs
+++ b/compiler/rustc_index/src/lib.rs
@@ -2,6 +2,7 @@
 #![cfg_attr(all(feature = "nightly", test), feature(stmt_expr_attributes))]
 #![cfg_attr(feature = "nightly", allow(internal_features))]
 #![cfg_attr(feature = "nightly", feature(extend_one, step_trait, test))]
+#![cfg_attr(feature = "nightly", feature(new_range_api))]
 #![cfg_attr(feature = "nightly", feature(new_zeroed_alloc))]
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end
@@ -14,7 +15,7 @@ mod idx;
 mod slice;
 mod vec;
 
-pub use idx::Idx;
+pub use idx::{Idx, IntoSliceIdx};
 pub use rustc_index_macros::newtype_index;
 pub use slice::IndexSlice;
 #[doc(no_inline)]
diff --git a/compiler/rustc_index/src/slice.rs b/compiler/rustc_index/src/slice.rs
index 956d32c9a69..cc8080ee697 100644
--- a/compiler/rustc_index/src/slice.rs
+++ b/compiler/rustc_index/src/slice.rs
@@ -1,8 +1,9 @@
+use std::fmt;
 use std::marker::PhantomData;
 use std::ops::{Index, IndexMut};
-use std::{fmt, slice};
+use std::slice::{self, SliceIndex};
 
-use crate::{Idx, IndexVec};
+use crate::{Idx, IndexVec, IntoSliceIdx};
 
 /// A view into contiguous `T`s, indexed by `I` rather than by `usize`.
 ///
@@ -99,13 +100,19 @@ impl<I: Idx, T> IndexSlice<I, T> {
     }
 
     #[inline]
-    pub fn get(&self, index: I) -> Option<&T> {
-        self.raw.get(index.index())
+    pub fn get<R: IntoSliceIdx<I, [T]>>(
+        &self,
+        index: R,
+    ) -> Option<&<R::Output as SliceIndex<[T]>>::Output> {
+        self.raw.get(index.into_slice_idx())
     }
 
     #[inline]
-    pub fn get_mut(&mut self, index: I) -> Option<&mut T> {
-        self.raw.get_mut(index.index())
+    pub fn get_mut<R: IntoSliceIdx<I, [T]>>(
+        &mut self,
+        index: R,
+    ) -> Option<&mut <R::Output as SliceIndex<[T]>>::Output> {
+        self.raw.get_mut(index.into_slice_idx())
     }
 
     /// Returns mutable references to two distinct elements, `a` and `b`.
@@ -186,19 +193,19 @@ impl<I: Idx, T: fmt::Debug> fmt::Debug for IndexSlice<I, T> {
     }
 }
 
-impl<I: Idx, T> Index<I> for IndexSlice<I, T> {
-    type Output = T;
+impl<I: Idx, T, R: IntoSliceIdx<I, [T]>> Index<R> for IndexSlice<I, T> {
+    type Output = <R::Output as SliceIndex<[T]>>::Output;
 
     #[inline]
-    fn index(&self, index: I) -> &T {
-        &self.raw[index.index()]
+    fn index(&self, index: R) -> &Self::Output {
+        &self.raw[index.into_slice_idx()]
     }
 }
 
-impl<I: Idx, T> IndexMut<I> for IndexSlice<I, T> {
+impl<I: Idx, T, R: IntoSliceIdx<I, [T]>> IndexMut<R> for IndexSlice<I, T> {
     #[inline]
-    fn index_mut(&mut self, index: I) -> &mut T {
-        &mut self.raw[index.index()]
+    fn index_mut(&mut self, index: R) -> &mut Self::Output {
+        &mut self.raw[index.into_slice_idx()]
     }
 }
 
-- 
cgit 1.4.1-3-g733a5