alist-get: Add optional arg TESTFN

If TESTFN is non-nil, then it is the predicate to lookup
the alist.  Otherwise, use 'eq' (Bug#27584).
* lisp/subr.el (alist-get): Add optional arg FULL.
* lisp/emacs-lisp/map.el (map-elt, map-put): Add optional arg TESTFN.
* lisp/emacs-lisp/gv.el (alist-get): Update expander.
* doc/lispref/lists.texi (Association Lists): Update manual.
* etc/NEWS: Announce the changes.
* test/lisp/emacs-lisp/map-tests.el (test-map-put-testfn-alist)
(test-map-elt-testfn): New tests.

1 files changed, 3 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index edb71118efd..dca562cb3b9 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1119,6 +1119,9 @@ break.
 
 * Lisp Changes in Emacs 26.1
 
++++
+** New optional argument TESTFN in 'alist-get', 'map-elt' and 'map-put'.
+
 ** New function 'seq-set-equal-p' to check if SEQUENCE1 and SEQUENCE2
 contain the same elements, regardless of the order.