From 2ef8d60cc6d65e6dbc11194f65856ad5aa43c27e Mon Sep 17 00:00:00 2001
From: Ben Greenman <benjaminlgreenman@gmail.com>
Date: Sun, 5 Aug 2018 23:53:49 -0400
Subject: [PATCH] improve `hash-ref` error message for non-thunk failure
 procedure (#2204)

Improve the `hash-ref` error message when the failure result does not
accept zero arguments. (This only changes what the error messages says.)

Example:
```(hash-ref #hash() 'a add1)```

Old message:
```
; add1: arity mismatch;
;  the expected number of arguments does not match the given number
;   expected: 1
;   given: 0
```

New message:
```
; hash-ref: contract violation
;   expected: (-> any)
;   given: #<procedure:add1>
;   argument position: 3rd
```
---
 pkgs/racket-test-core/tests/racket/basic.rktl | 2 +-
 racket/src/racket/src/list.c                  | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/pkgs/racket-test-core/tests/racket/basic.rktl b/pkgs/racket-test-core/tests/racket/basic.rktl
index 5dc3955473..070de07506 100644
--- a/pkgs/racket-test-core/tests/racket/basic.rktl
+++ b/pkgs/racket-test-core/tests/racket/basic.rktl
@@ -2191,7 +2191,7 @@
       (test #t eq? (equal-hash-code l) (equal-hash-code (list 1 2 3)))
       (hash-set! h1 l 'ok)
       (test 'ok hash-ref h1 l)
-      (err/rt-test (hash-ref h1 'nonesuch (lambda (x) 'bad-proc)) exn:fail:contract:arity?)
+      (err/rt-test (hash-ref h1 'nonesuch (lambda (x) 'bad-proc)) exn:fail:contract? "hash-ref")
       (test #t hash-has-key? h1 l)
       (test #f hash-has-key? h1 (cdr l))
       (when hash-ref!
diff --git a/racket/src/racket/src/list.c b/racket/src/racket/src/list.c
index 4355e3c250..77f5206b2e 100644
--- a/racket/src/racket/src/list.c
+++ b/racket/src/racket/src/list.c
@@ -2603,9 +2603,10 @@ static Scheme_Object *hash_failed(int argc, Scheme_Object *argv[])
 
   if (argc == 3) {
     v = argv[2];
-    if (SCHEME_PROCP(v))
+    if (SCHEME_PROCP(v)) {
+      scheme_check_proc_arity("hash-ref", 0, 2, argc, argv);
       return _scheme_tail_apply(v, 0, NULL);
-    else
+    } else
       return v;
   } else {
     scheme_contract_error("hash-ref",