Better error msg for structs with the same name

Thanks to Max for the suggestion

typed-racket-lib/typed-racket/typecheck/error-message.rkt

@@ -51,6 +51,11 @@
      ;;        prints the binding locations of each type variable.
      (type-mismatch (format "`~a'" t1) (format "a different `~a'" t2)
                     "type variables bound in different scopes")]
+    [((Struct: n1 _ _ _ _ _) (Struct: n2 _ _ _ _ _))
+     #:when (and (not (free-identifier=? n1 n2))
+                 (eq? (syntax-e n1) (syntax-e n2)))
+     (type-mismatch (syntax-e n1) (format "a different ~a" (syntax-e n2))
+                    "incompatible struct types with the same name")]
     [((? Class?) (? Class?))
      (class-mismatch r1 r2)]
     [((Instance: (app resolve (? Class? c1))) (Instance: (app resolve (? Class? c2))))

typed-racket-test/fail/same-name-struct-type.rkt

@@ -0,0 +1,20 @@
+#;
+(exn-pred #rx"incompatible struct types with the same name")
+#lang racket/load
+
+;; Test the error message for subtyping errors on struct types
+;; with the same name
+
+(module a typed/racket
+  (struct foo ([x : Integer]))
+  (define a-foo (foo 3))
+  (provide a-foo))
+
+(module b typed/racket
+  (struct foo ([x : String]))
+  (define (f [a-foo : foo]) (foo-x a-foo))
+  (provide f))
+
+(module c typed/racket
+  (require 'a 'b)
+  (f a-foo))