bug#22449: (rnrs hashtables): Mutation of immutable hashtable ignored

["Taylan Ulrich Bayırlı/Kammer"]

I couldn't find explicit wording in R6RS on what should happen, but I
would generally expect an attempt to mutate an immutable object to
raise an error.  In Guile,

    (hashtable-set! (hashtable-copy (make-eq-hashtable)) 'foo 'bar)

is silently ignored.

Attached is a simple patch that raises an assertion violation when the
hashtable is immutable.

Taylan

===File
/home/taylan/src/guile/guile-stable-2.0/0001-Hashtable-set-errors-on-immutable-hashtable.patch===
>From dd6c4bbbe85a57fcbb08bdc7847075bddc1f0d87 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Taylan=20Ulrich=20Bay=C4=B1rl=C4=B1/Kammer?=
 <address@hidden>
Date: Sat, 23 Jan 2016 22:35:24 +0100
Subject: [PATCH] Hashtable-set! errors on immutable hashtable.

* module/rnrs/hashtables.scm (hashtable-set!): Raise an assertion
  violation error when the hashtable is immutable.
---
 module/rnrs/hashtables.scm | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/module/rnrs/hashtables.scm b/module/rnrs/hashtables.scm
index 98d2d76..5773eb1 100644
--- a/module/rnrs/hashtables.scm
+++ b/module/rnrs/hashtables.scm
@@ -122,8 +122,9 @@
 
   (define (hashtable-set! hashtable key obj)
     (if (r6rs:hashtable-mutable? hashtable)
-       (hash-table-set! (r6rs:hashtable-wrapped-table hashtable) key obj))
-    *unspecified*)
+        (hash-table-set! (r6rs:hashtable-wrapped-table hashtable) key obj)
+        (assertion-violation
+         'hashtable-set! "Hashtable is immutable." hashtable)))
 
   (define (hashtable-delete! hashtable key)
     (if (r6rs:hashtable-mutable? hashtable)
-- 
2.6.3

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