Specify erasure of intersection types for the semantics of await expressions

Author: eernstg

specification/dartLangSpec.tex

@@ -17111,8 +17111,12 @@ \subsection{Await Expressions}
 
 \LMHash{}%
 Evaluation of an await expression $a$ of the form \code{\AWAIT{} $e$}
-where $e$ has static type $S$ proceeds as follows:
+where $e$ has static type $S_0$ proceeds as follows:
 First, the expression $e$ is evaluated to an object $o$.
+If $S_0$ is of the form \code{$X$\,\,\&\,\,$S_1$}
+(\ref{intersectionTypes})
+then let $S$ be $X$.
+Otherwise, let $S$ be $S_0$.
 Let $T$ be \Flatten{$S$}
 (\ref{functionExpressions}).
 It is a dynamic type error if the run-time type of $o$ is not a subtype
@@ -26039,7 +26043,7 @@ \section*{Appendix: Algorithmic Subtyping}
   if $T_0$ is a type variable $X_0$
   or a promoted type variables \code{$X_0$\,\&\,$S_0$} and $T_1$ is $X_0$
   then \SubtypeNE{T_0}{T_1}.
-  
+
   \commentary{%
     Note that this rule is admissible, and can be safely elided if desired.%
   }