Merge pull request #49029 from DavidSouther/fix/44466-contextual-keyword-assertion

fix(44466): Fixes parsing contextual keyword casts as arrow functions

src/compiler/parser.ts

@@ -4538,6 +4538,10 @@ namespace ts {
                 // isn't actually allowed, but we want to treat it as a lambda so we can provide
                 // a good error message.
                 if (isModifierKind(second) && second !== SyntaxKind.AsyncKeyword && lookAhead(nextTokenIsIdentifier)) {
+                    if (nextToken() === SyntaxKind.AsKeyword) {
+                        // https://github.com/microsoft/TypeScript/issues/44466
+                        return Tristate.False;
+                    }
                     return Tristate.True;
                 }