fix bug in the ->i parser (picked up the wrong identifier; wrote #'id when

id wasn't really around anywhere)

closes PR 12829

collects/racket/contract/private/arr-i-parse.rkt

@@ -297,7 +297,7 @@ code does the parsing and validation of the syntax.
     [[_ (id2 ...) ctc] 
      (begin
        (for-each (λ (x) (check-id stx x)) (syntax->list #'(id2 ...)))
-       (list (eres #'id (syntax->list #'(id2 ...)) #'ctc (car (generate-temporaries '(eres))))))]
+       (list (eres #'_ (syntax->list #'(id2 ...)) #'ctc (car (generate-temporaries '(eres))))))]
     [[id (id2 ...) ctc] 
      (begin
        (check-id stx #'id)

collects/tests/racket/contract-test.rktl

@@ -12642,6 +12642,14 @@ so that propagation occurs.
                           'pos
                           'neg))))
   
+  (ctest '("the _ result of")
+         extract-context-lines
+         (λ () ((contract (->i ([x integer?]) [_ (x) (<=/c x)])
+                          add1
+                          'pos
+                          'neg)
+                1)))
+  
   (ctest '("the a argument of") 
          extract-context-lines 
          (λ () ((contract (->i ([a integer?] #:b [b integer?]) ([c integer?] #:d [d integer?]) any)