Rollup merge of #104976 - WaffleLapkin:move_comments, r=cjgillot

Prefer doc comments over `//`-comments in compiler

Doc comments are generally nicer: they show up in the documentation, they are shown in IDEs when you hover other mentions of items, etc. Thus it makes sense to use them instead of `//`-comments.

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -417,8 +417,8 @@ pub trait Machine<'mir, 'tcx>: Sized {
     }
 }
 
-// A lot of the flexibility above is just needed for `Miri`, but all "compile-time" machines
-// (CTFE and ConstProp) use the same instance.  Here, we share that code.
+/// A lot of the flexibility above is just needed for `Miri`, but all "compile-time" machines
+/// (CTFE and ConstProp) use the same instance.  Here, we share that code.
 pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     type Provenance = AllocId;
     type ProvenanceExtra = ();

compiler/rustc_const_eval/src/interpret/projection.rs

@@ -206,8 +206,8 @@ where
         }
     }
 
-    // Iterates over all fields of an array. Much more efficient than doing the
-    // same by repeatedly calling `operand_index`.
+    /// Iterates over all fields of an array. Much more efficient than doing the
+    /// same by repeatedly calling `operand_index`.
     pub fn operand_array_fields<'a>(
         &self,
         base: &'a OpTy<'tcx, Prov>,

compiler/rustc_const_eval/src/interpret/visitor.rs

@@ -324,7 +324,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M>
 
 macro_rules! make_value_visitor {
     ($visitor_trait:ident, $value_trait:ident, $($mutability:ident)?) => {
-        // How to traverse a value and what to do when we are at the leaves.
+        /// How to traverse a value and what to do when we are at the leaves.
         pub trait $visitor_trait<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized {
             type V: $value_trait<'mir, 'tcx, M>;