clean up `define-syntax-rules'

by removing a redundant expression in an error message, adding
 tests, and documenting the fact that a syntax-error message can
 expose the pattern source to users

collects/racket/private/misc.rkt

@@ -26,10 +26,10 @@
                           ([(sexpr) (syntax->datum user-stx)]
                            [(msg)
                             (if (pair? sexpr)
-                              (format "~.s did not match pattern ~.s"
+                              (format "use does not match pattern: ~.s"
-                                      sexpr (cons (car sexpr) 'pattern))
+                                      (cons (car sexpr) 'pattern))
                               (if (symbol? sexpr)
-                                (format "must be used in a pattern ~.s"
+                                (format "use does not match pattern: ~.s"
                                         (cons sexpr 'pattern))
                                 (error 'internal-error
                                        "something bad happened")))])

collects/scribblings/reference/stx-patterns.scrbl

@@ -469,7 +469,9 @@ Equivalent to
   (syntax-rules ()
    [(id . pattern) template]))
 ]
-}
+
+but with syntax errors potentially phrased in terms of 
+@racket[pattern].}
 
 
 @defidform[...]{

collects/tests/racket/stx.rktl

@@ -1456,6 +1456,27 @@
                (get-output-bytes s))
              exn:fail?)
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; define-syntax-rule
+
+(define-syntax-rule (a-rule-pattern x [y z])
+  (list 'x 'y 'z))
+
+(test '(1 2 3) 'a-rule (a-rule-pattern 1 [2 3]))
+(test '(1 2 3) 'a-rule (a-rule-pattern 1 . ([2 3])))
+(test '(1 2 3) 'a-rule (a-rule-pattern 1 [2 . (3)]))
+(syntax-test #'a-rule-pattern)
+(syntax-test #'(a-rule-pattern 1 2 3))
+(syntax-test #'(a-rule-pattern 1 . 2))
+(syntax-test #'(a-rule-pattern . 1))
+(syntax-test #'(a-rule-pattern 1 [2 3] 4))
+
+(let ([no-match? (lambda (exn) 
+                   (regexp-match? #"does not match pattern" (exn-message exn)))])
+  (error-test #'a-rule-pattern no-match?)
+  (error-test #'(a-rule-pattern) no-match?)
+  (error-test #'(a-rule-pattern 1) no-match?))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)