cs & regexp: report unmatched )

Closes #3854

pkgs/racket-test-core/tests/racket/basic.rktl

@@ -1521,6 +1521,8 @@
 ;; Regexps that shouldn't work:
 (err/rt-test (regexp "[a--b]") exn:fail?)
 (err/rt-test (regexp "[a-b-c]") exn:fail?)
+(err/rt-test (regexp "abc)") exn:fail?)
+(err/rt-test (pregexp "abc)") exn:fail?)
 
 ;; A good test of unicode-friendly ".":
 (test '("load-extension: couldn't open \\\" (%s)\"") 

racket/src/cs/schemified/regexp.scm

@@ -2972,13 +2972,20 @@
           (lambda () (parse-regexp.1 unsafe-undefined p3_0 0 config_0))
           (case-lambda
            ((rx_0 pos_0)
-            (let ((app_0
-                   (begin-unsafe
-                    (unbox (parse-config-group-number-box config_0)))))
-              (values
-               rx_0
-               app_0
-               (unbox (parse-config-references?-box config_0)))))
+            (let ((pos_1 pos_0))
+              (let ((tmp_0
+                     (if (let ((app_0 pos_1)) (= app_0 (chytes-length$1 p3_0)))
+                       'eos
+                       (chytes-ref/char p3_0 pos_1))))
+                (if (eqv? tmp_0 '#\x29)
+                  (parse-error p3_0 pos_0 config_0 "unmatched `)` in pattern")
+                  (let ((app_0
+                         (begin-unsafe
+                          (unbox (parse-config-group-number-box config_0)))))
+                    (values
+                     rx_0
+                     app_0
+                     (unbox (parse-config-references?-box config_0))))))))
            (args (raise-binding-result-arity-error 2 args)))))))))
 (define parse-regexp.1
   (|#%name|

racket/src/regexp/parse/main.rkt

@@ -15,9 +15,14 @@
 (define (parse p #:px? [px? #f])
   (define config (make-parse-config #:px? px?))
   (define-values (rx pos) (parse-regexp p 0 config))
-  (values rx
-          (config-group-number config)
-          (unbox (parse-config-references?-box config))))
+  (chyte-case/eos
+   p pos
+   [(#\))
+    (parse-error p pos config "unmatched `)` in pattern")]
+   [else
+    (values rx
+            (config-group-number config)
+            (unbox (parse-config-references?-box config)))]))
 
 ;; Returns (values rx position)
 (define (parse-regexp s pos config #:parse-regexp [parse-regexp (lambda (s pos config)