syntax/parse: fix handling of ~seq with action patterns

pkgs/racket-test/tests/stxparse/test.rkt

@@ -1043,3 +1043,14 @@
       (syntax-parse #'#f
         [_:indirect-bad #t]
         [_ #f])))))
+
+;; from turnstile, action pattern in ~seq (6/2019)
+(let ()
+  ;; The regression required the following circumstances:
+  ;; - the action pattern must be able to fail, so subsequent pattern gets an ORD frame
+  ;; - the ~seq cannot be inlined away, like (a (~seq b c) d) => (a b c d), so use ~or
+  (convert-syntax-error
+   (syntax-parse #'(m 1 2 3)
+     [(_ (~or (~seq a b c (~parse (d e f) #'(a b c)))
+              (~seq x:id ...)))
+      (void)])))

racket/collects/syntax/parse/private/rep.rkt

@@ -1392,6 +1392,10 @@
       [(pat:action ap sp) (pat:action ap (loop sp))]
       [(pat:head hp tp) (pat:head hp (loop tp))]
       [(pat:dots hs tp) (pat:dots hs (loop tp))]
+      [(pat:ord sp group index)
+       ;; This is awkward, but it is needed to pop the ORD progress frame on success.
+       (define sp* (list-pattern-replace-end sp (pat:seq-end)))
+       (pat:head (hpat:ord (hpat:seq sp*) group index) endp)]
       [(pat:pair hp tp) (pat:pair hp (loop tp))])))
 
 ;; ----------------------------------------