Add an optional testfn parameter to assoc

* src/fns.c (assoc): New optional testfn parameter used for comparison
when provided.
* test/src/fns-tests.el (test-assoc-testfn): Add tests for the new
'testfn' parameter.
* src/buffer.c:
* src/coding.c:
* src/dbusbind.c:
* src/font.c:
* src/fontset.c:
* src/gfilenotify.c:
* src/image.c:
* src/keymap.c:
* src/process.c:
* src/w32fns.c:
* src/w32font.c:
* src/w32notify.c:
* src/w32term.c:
* src/xdisp.c:
* src/xfont.c: Add a third argument to Fassoc calls.
* etc/NEWS:
* doc/lispref/lists.texi: Document the new 'testfn' parameter.

1 files changed, 10 insertions, 5 deletions

diff --git a/src/fns.c b/src/fns.c
index 6610d2a6d0e..f0e10e311f5 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -1417,17 +1417,22 @@ assq_no_quit (Lisp_Object key, Lisp_Object list)
   return Qnil;
 }
 
-DEFUN ("assoc", Fassoc, Sassoc, 2, 2, 0,
-       doc: /* Return non-nil if KEY is `equal' to the car of an element of LIST.
-The value is actually the first element of LIST whose car equals KEY.  */)
-  (Lisp_Object key, Lisp_Object list)
+DEFUN ("assoc", Fassoc, Sassoc, 2, 3, 0,
+       doc: /* Return non-nil if KEY is equal to the car of an element of LIST.
+The value is actually the first element of LIST whose car equals KEY.
+
+Equality is defined by TESTFN if non-nil or by `equal' if nil.  */)
+     (Lisp_Object key, Lisp_Object list, Lisp_Object testfn)
 {
   Lisp_Object tail = list;
   FOR_EACH_TAIL (tail)
     {
       Lisp_Object car = XCAR (tail);
       if (CONSP (car)
-          && (EQ (XCAR (car), key) || !NILP (Fequal (XCAR (car), key))))
+          && (NILP (testfn)
+              ? (EQ (XCAR (car), key) || !NILP (Fequal
+                                                (XCAR (car), key)))
+              : !NILP (call2 (testfn, XCAR (car), key))))
         return car;
     }
   CHECK_LIST_END (tail, list);