Prefer doc comments over //-comments in compiler

compiler/rustc_parse/src/parser/attr_wrapper.rs

@@ -50,7 +50,7 @@ impl AttrWrapper {
         self.attrs
     }
 
-    // Prepend `self.attrs` to `attrs`.
+    /// Prepend `self.attrs` to `attrs`.
     // FIXME: require passing an NT to prevent misuse of this method
     pub(crate) fn prepend_to_nt_inner(self, attrs: &mut AttrVec) {
         let mut self_attrs = self.attrs;

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -224,9 +224,9 @@ impl MultiSugg {
     }
 }
 
-// SnapshotParser is used to create a snapshot of the parser
-// without causing duplicate errors being emitted when the `Parser`
-// is dropped.
+/// SnapshotParser is used to create a snapshot of the parser
+/// without causing duplicate errors being emitted when the `Parser`
+/// is dropped.
 pub struct SnapshotParser<'a> {
     parser: Parser<'a>,
     unclosed_delims: Vec<UnmatchedBrace>,