Add more documentation

rust-lang · Jan 7, 2020 · 29c372b · 29c372b
1 parent f7f5952
commit 29c372b
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Showing 2 changed files with 8 additions and 1 deletion.
diff --git a/src/librustc_mir/const_eval/eval_queries.rs b/src/librustc_mir/const_eval/eval_queries.rs
@@ -124,7 +124,12 @@ pub(super) fn op_to_const<'tcx>(
             ConstValue::ByRef { alloc, offset: ptr.offset }
         }
         Scalar::Raw { data, .. } => {
-            assert_eq!(data, mplace.layout.align.abi.bytes().into());
+            assert_eq!(
+                data,
+                mplace.layout.align.abi.bytes().into(),
+                "this MPlaceTy must come from `try_as_mplace` being used on a zst, so we know what
+                 value this integer address must have",
+            );
             assert!(mplace.layout.is_zst());
             ConstValue::Scalar(Scalar::zst())
         }

diff --git a/src/librustc_mir/interpret/place.rs b/src/librustc_mir/interpret/place.rs
@@ -21,7 +21,9 @@ use super::{
 };
 
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, HashStable)]
+/// Information required for the sound usage of a `MemPlace`.
 pub enum MemPlaceMeta<Tag = (), Id = AllocId> {
+    /// The unsized payload (e.g. length for slices or vtable pointer for trait objects).
     Unsized(Scalar<Tag, Id>),
     /// `Sized` types or unsized `extern type`
     None,