Double-check that neighbors have neighboring srclocs

With code like `(a b c . -> . d)`, which uses racket's infix `.` notation, the "are these syntax objects neighbors?" check goes a little sideways. This fix seems to mostly deal with the issue. Maybe.

default-recommendations/contract-shortcuts.rkt

@@ -53,15 +53,13 @@
 (define-refactoring-rule arrow-contract-with-rest-to-arrow-contract-with-ellipses
   #:description "This `->*` contract can be rewritten using `->` with ellipses."
   #:literals (->* listof)
-  [((~and arrow-id ->*)
-    (~and args (arg-contract ...))
+  [(->*
+    (arg-contract ...)
     (~optional ())
-    (~and rest-kw #:rest) (~and rest-list (listof rest-contract))
+    #:rest (~and rest-list (listof rest-contract))
     result-contract)
-   (-> (ORIGINAL-GAP arrow-id args)
-       arg-contract ...
+   (-> arg-contract ...
        rest-contract (... ...)
-       (ORIGINAL-GAP rest-list result-contract)
        result-contract)])
 
 

private/syntax-neighbors.rkt

@@ -47,9 +47,12 @@
        (for/list ([leading (in-list leading-neighbors)]
                   [trailing (in-list trailing-neighbors)]
                   [subform-stx (in-list (attribute subform))])
+         (define leading-pos (and leading (syntax-position leading)))
+         (define trailing-pos (and trailing (syntax-position trailing)))
+         (define subform-pos (syntax-position subform-stx))
          (mark-neighbors (syntax-mark-original-neighbors subform-stx)
-                         #:leading-neighbor leading
-                         #:trailing-neighbor trailing)))
+                         #:leading-neighbor (and leading (< leading-pos subform-pos) leading)
+                         #:trailing-neighbor (and trailing (< subform-pos trailing-pos) trailing))))
      (datum->syntax stx results stx stx)]
     [_ stx]))