it appears that the check for empty list when the depth is 'unknown-mismatch-depth was overzealous

The way that things work, as soon as there is something in the one of the nested lists that needs to be checked to make sure they are different, then we're going to get the correct depth in `nesting-depth`

closes #268

Author: rfindler

redex-lib/redex/private/matcher.rkt

@@ -690,24 +690,17 @@ See match-a-pattern.rkt for more details
              (define table (make-hash))
              (hash-set! mismatch-ht name table)
              (set! priors table))
-           (cond
-             [(equal? nesting-depth 'unknown-mismatch-depth)
-              (unless (null? exp)
-                (error 'matcher.rkt 
-                       (string-append "invariant broken; unknown-mismatch-depth should"
-                                      " appear only when the expression is an empty list: ~s")
-                       exp))]
-             [else
-              (let loop ([depth nesting-depth]
-                         [exp exp])
-                (cond
-                  [(= depth 0)
-                   (when (hash-ref priors exp #f)
-                     (fail #f))
-                   (hash-set! priors exp #t)]
-                  [else
-                   (for ([exp-ele (in-list exp)])
-                     (loop (- depth 1) exp-ele))]))])]))
+           (unless (equal? nesting-depth 'unknown-mismatch-depth)
+             (let loop ([depth nesting-depth]
+                        [exp exp])
+               (cond
+                 [(= depth 0)
+                  (when (hash-ref priors exp #f)
+                    (fail #f))
+                  (hash-set! priors exp #t)]
+                 [else
+                  (for ([exp-ele (in-list exp)])
+                    (loop (- depth 1) exp-ele))])))]))
       (make-bindings (hash-map match-ht make-bind)))))
 
 ;; compile-pattern : compiled-lang pattern boolean -> compiled-pattern

redex-test/redex/tests/matcher-test.rkt

@@ -176,6 +176,30 @@
                                                       (make-bind '..._1 2)))
                                  '(1 1 1 1 2 2)
                                  none)))
+    (test-empty '(list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f))
+                '(())
+                (list (make-mtch (make-bindings '()) '(()) none)))
+    (test-empty '(list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f))
+                '(() ())
+                (list (make-mtch (make-bindings '()) '(() ()) none)))
+    (test-empty '(list (repeat (list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f)) #f #f))
+                '(() ())
+                (list (make-mtch (make-bindings '()) '(() ()) none)))
+    (test-empty '(list (repeat (list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f)) #f #f))
+                '(() (()))
+                (list (make-mtch (make-bindings '()) '(() (())) none)))
+    (test-empty '(list (repeat (list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f)) #f #f))
+                '(() ((())))
+                #f)
+    (test-empty '(list (repeat (list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f)) #f #f))
+                '(() ((1)))
+                (list (make-mtch (make-bindings '()) '(() ((1))) none)))
+    (test-empty '(list (repeat (list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f)) #f #f))
+                '(() (()))
+                (list (make-mtch (make-bindings '()) '(() (())) none)))
+    (test-empty '(list (repeat (list (repeat (list (repeat (mismatch-name number_!_ number) #f #f)) #f #f)) #f #f))
+                '(() (1))
+                #f)
 
     (test-ellipses '(a) '(a))
     (test-ellipses '((repeat a #f #f)) `(,(make-repeat 'a '() #f #f)))