Changed define-predicate to use recursive-contract. Closes PR 10939.

Closes PR11504.

original commit: 76a1112df03083098dc5aaff951d9e768e5af1b6

collects/tests/typed-scheme/succeed/pr10939.rkt

@@ -0,0 +1,8 @@
+#lang typed/scheme
+
+(define-type (T elem)
+  (U 'other a:empty))
+
+(define-predicate a:list? (T Any))
+
+(define-struct: a:empty ())

collects/tests/typed-scheme/succeed/pr11504.rkt

@@ -0,0 +1,7 @@
+#lang typed/racket
+
+(define-type Animal (U cat dog))
+(define-predicate animal? Animal)
+
+(struct: cat ([lives : Natural]))
+(struct: dog ([bark : Natural] [bite : Natural]))

collects/typed-scheme/private/type-contract.rkt

@@ -40,7 +40,7 @@
                            #:typed-side #f
                            #:flat flat?
                            (lambda () (tc-error/stx prop "Type ~a could not be converted to a contract." typ)))])
-         (syntax/loc stx (define-values (n) cnt))))]
+         (quasisyntax/loc stx (define-values (n) (recursive-contract cnt #,(if flat? #'#:flat #'#:impersonator))))))]
     [_ (int-err "should never happen - not a define-values: ~a" (syntax->datum stx))]))
 
 (define (change-contract-fixups forms)