let_chains: Improve documentation for ast::ExprKind::Let(..).

src/libsyntax/ast.rs

@@ -1115,8 +1115,11 @@ pub enum ExprKind {
     Cast(P<Expr>, P<Ty>),
     /// A type ascription (e.g., `42: usize`).
     Type(P<Expr>, P<Ty>),
-    /// A `let pat = expr` pseudo-expression that only occurs in the scrutinee
+    /// A `let pats = expr` pseudo-expression that only occurs in the scrutinee
     /// of `if` / `while` expressions. (e.g., `if let 0 = x { .. }`).
+    ///
+    /// The `Vec<P<Pat>>` is for or-patterns at the top level.
+    /// FIXME(54883): Change this to just `P<Pat>`.
     Let(Vec<P<Pat>>, P<Expr>),
     /// An `if` block, with an optional `else` block.
     ///