Fix error message for misuse of #:methods

Closes PR 14069

pkgs/racket-pkgs/racket-test/tests/generic/errors.rkt

@@ -43,6 +43,13 @@
                                   #:methods gen:foobar
                                   [(define foo 0)])
                           'ignore))))
+  ;; Test for PR 14069, make sure that the error reports
+  ;; the faulty syntax as `bar` and not `#:methods`
+  (check-exn #rx"at: bar"
+             (lambda () (convert-compile-time-error
+                         (let ()
+                          (struct foo () #:methods bar [])
+                          'ignore))))
   (check-exn #rx"foo: not implemented for 5"
              (lambda () (let ()
                           (define-generics foobar

racket/collects/racket/private/define-struct.rkt

@@ -291,9 +291,10 @@
             (and (identifier? gen-id)
                  (syntax-local-value gen-id (lambda () #f))))
           (unless (generic-info? gen-val)
-            (bad "the first argument to the "
+            (bad "the first argument to the"
                  (car p)
-                 " is not a name for a generic interface"))
+                 " is not a name for a generic interface"
+                 (cadr p)))
           (loop (list* #'#:property
                        (quasisyntax/loc gen-id
                          (generic-property #,gen-id))