Implement 'func-arity'

* src/eval.c (Ffunc_arity, lambda_arity): New functions.
* src/bytecode.c (get_byte_code_arity): New function.
* src/lisp.h (get_byte_code_arity): Add prototype.

* doc/lispref/functions.texi (What Is a Function): Document
'func-arity'.

* etc/NEWS: Mention 'func-arity'.

* test/src/fns-tests.el (fns-tests-func-arity): New test set.

1 files changed, 7 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 0bc61308945..ce21532b68d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -182,6 +182,13 @@ a new window when opening man pages when there's already one, use
         (mode . Man-mode))))
 
 +++
+** New function 'func-arity' returns information about the argument list
+of an arbitrary function.
+This is a generalization of 'subr-arity' for functions that are not
+built-in primitives.  We recommend using this new function instead of
+'subr-arity'.
+
++++
 ** 'parse-partial-sexp' state has a new element.  Element 10 is
 non-nil when the last character scanned might be the first character
 of a two character construct, i.e. a comment delimiter or escaped