clarify semantics of ConstantIndex MIR projection

rust-lang · Oct 5, 2024 · f0ddc7b · f0ddc7b
1 parent 5a4ee43
commit f0ddc7b
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
@@ -1135,8 +1135,10 @@ pub enum ProjectionElem<V, T> {
     ConstantIndex {
         /// index or -index (in Python terms), depending on from_end
         offset: u64,
-        /// The thing being indexed must be at least this long. For arrays this
-        /// is always the exact length.
+        /// The thing being indexed must be at least this long -- otherwise, the
+        /// projection is UB.
+        ///
+        /// For arrays this is always the exact length.
         min_length: u64,
         /// Counting backwards from end? This is always false when indexing an
         /// array.

diff --git a/compiler/stable_mir/src/mir/body.rs b/compiler/stable_mir/src/mir/body.rs
@@ -768,8 +768,10 @@ pub enum ProjectionElem {
     ConstantIndex {
         /// index or -index (in Python terms), depending on from_end
         offset: u64,
-        /// The thing being indexed must be at least this long. For arrays this
-        /// is always the exact length.
+        /// The thing being indexed must be at least this long -- otherwise, the
+        /// projection is UB.
+        ///
+        /// For arrays this is always the exact length.
         min_length: u64,
         /// Counting backwards from end? This is always false when indexing an
         /// array.