Handle single-argument `apply' consistently (bug#40968)

* src/eval.c (Fapply): Handle (apply nil) without crashing.
Document single-argument form.
* lisp/emacs-lisp/byte-opt.el (byte-optimize-apply): Don't attempt
to optimize single-argument apply.
* doc/lispref/functions.texi (Calling Functions): Document
single-argument apply.  Provide example (bug#40968).

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/lispref/functions.texi b/doc/lispref/functions.texi
index 26b212d05eb..e8e22078d9b 100644
--- a/doc/lispref/functions.texi
+++ b/doc/lispref/functions.texi
@@ -762,6 +762,11 @@ arguments, rather than a single list.  We say that @code{apply}
 @dfn{spreads} this list so that each individual element becomes an
 argument.
 
+@code{apply} with a single argument is special: the first element of
+the argument, which must be a non-empty list, is called as a function
+with the remaining elements as individual arguments.  Passing two or
+more arguments will be faster.
+
 @code{apply} returns the result of calling @var{function}.  As with
 @code{funcall}, @var{function} must either be a Lisp function or a
 primitive function; special forms and macros do not make sense in
@@ -789,6 +794,11 @@ primitive function; special forms and macros do not make sense in
 (apply 'append '((a b c) nil (x y z) nil))
      @result{} (a b c x y z)
 @end group
+
+@group
+(apply '(+ 3 4))
+     @result{} 7
+@end group
 @end example
 
 For an interesting example of using @code{apply}, see @ref{Definition