fix inference with define-new-subtype

typed-racket-lib/typed-racket/infer/infer-unit.rkt

@@ -540,6 +540,13 @@
                         #:when v)
               v))]
 
+          ;; from define-new-subtype
+          [((Distinction: nm1 id1 S) (app resolve (Distinction: nm2 id2 T)))
+           #:when (and (equal? nm1 nm2) (equal? id1 id2))
+           (cg S T)]
+          [((Distinction: _ _ S) T)
+           (cg S T)]
+
           ;; two structs with the same name
           ;; just check pairwise on the fields
           [((Struct: nm _ flds proc _ _) (Struct: nm* _ flds* proc* _ _))

typed-racket-test/succeed/define-new-subtype-infer.rkt

@@ -0,0 +1,8 @@
+#lang typed/racket
+
+(define-new-subtype T (make-T (List Integer)))
+
+(: f : T -> Integer)
+(define (f t)
+  (define x (car t))
+  (* x 2))