Rule out multiple super-new

pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/typecheck/check-class-unit.rkt

@@ -398,7 +398,11 @@
          (tc-error/expr
           "typed classes must call super-new at the class top-level")
          null]
-        [else
+        [(> (length super-new-stx) 1)
+         (tc-error/expr
+          "typed classes must only call super-new a single time")
+         null]
+        [(= (length super-new-stx) 1)
          (syntax-parse (car super-new-stx)
            #:literals (#%plain-app list cons quote)
            [(#%plain-app super-go _ _ _ _ _

pkgs/typed-racket-pkgs/typed-racket-test/tests/typed-racket/unit-tests/class-tests.rkt

@@ -385,6 +385,12 @@
                  (super-new [x 3])))
     (new c% [x 5]))
 
+   ;; fails, super-new can only be called once per class
+   (check-err
+    (class: object%
+      (super-new)
+      (super-new)))
+
    ;; test different internal/external names
    (check-ok
     (define c% (class: object% (super-new)