bug#40968: 28.0.50; (apply nil)

[Pip Cet <pipcet@gmail.com>]

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On Wed, May 6, 2020 at 10:18 AM Mattias Engdegård <mattiase@acm.org> wrote:
> > The byte compiler also gets single-argument `apply' "wrong", so the latter would seem to be the best option, to me.
>
> Strong agreement! An 'apply' that actually does 'eval'...

Well, it's not quite `eval': the arguments aren't evaluated again.

The obvious single-character patch results in four warnings when
rebuilding Emacs, all of which seem to use the previous semantics, so
I think it might be best to document this behavior and simply catch
(apply nil).

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From 898af394fcbde57ca3d08e3648b62fe0b3f41911 Mon Sep 17 00:00:00 2001
From: Pip Cet <pipcet@gmail.com>
Date: Wed, 6 May 2020 11:08:29 +0000
Subject: [PATCH] Require at least two arguments for Fapply

* src/eval.c (Fapply): Require at least two arguments, to prevent
crashes when (apply nil) is evaluated.
* lisp/progmodes/ebrowse.el (ebrowse-tags-loop-continue): Provide two
arguments to `apply'.
* lisp/svg.el (svg--eval-path-command): Provide two arguments to
`apply'.
* lisp/simple.el (primitive-undo): Provide two arguments to `apply'.
---
 lisp/net/telnet.el        | 3 ++-
 lisp/progmodes/ebrowse.el | 3 ++-
 lisp/simple.el            | 2 +-
 lisp/svg.el               | 3 ++-
 src/eval.c                | 2 +-
 5 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/lisp/net/telnet.el b/lisp/net/telnet.el
index e8c0c1bbdf..b0350eacbf 100644
--- a/lisp/net/telnet.el
+++ b/lisp/net/telnet.el
@@ -109,7 +109,8 @@ telnet-revert-buffer
         (revert-buffer ignore-auto noconfirm))
     (if (or noconfirm
             (yes-or-no-p (format "Restart connection? ")))
-        (apply telnet-connect-command))))
+        (apply (car telnet-connect-command)
+               (cdr telnet-connect-command)))))
 
 (defun telnet-c-z ()
   (interactive)
diff --git a/lisp/progmodes/ebrowse.el b/lisp/progmodes/ebrowse.el
index 1c9e805f03..f052266b1a 100644
--- a/lisp/progmodes/ebrowse.el
+++ b/lisp/progmodes/ebrowse.el
@@ -3612,7 +3612,8 @@ ebrowse-tags-loop-continue
   (when first-time
     (ebrowse-tags-next-file first-time tree-buffer)
     (goto-char (point-min)))
-  (while (not (apply ebrowse-tags-loop-call))
+  (while (not (apply (car ebrowse-tags-loop-call)
+                     (cdr ebrowse-tags-loop-call)))
     (ebrowse-tags-next-file)
     (message "Scanning file `%s'..." buffer-file-name)
     (goto-char (point-min))))
diff --git a/lisp/simple.el b/lisp/simple.el
index b5ba05426f..9a96ce0013 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2778,7 +2778,7 @@ primitive-undo
                      (error "Changes to be undone by function different from announced"))
                    (set-marker start-mark nil)
                    (set-marker end-mark nil))
-               (apply fun-args))
+               (apply (car fun-args) (cdr fun-args)))
              (unless (eq currbuff (current-buffer))
                (error "Undo function switched buffer"))
              (setq did-apply t)))
diff --git a/lisp/svg.el b/lisp/svg.el
index 7aadbc2359..982e2b0965 100644
--- a/lisp/svg.el
+++ b/lisp/svg.el
@@ -437,7 +437,8 @@ svg--eval-path-command
         #'svg--elliptical-arc-command)
        (extended-command (append command (list :default-relative
                                                default-relative))))
-    (mapconcat 'prin1-to-string (apply extended-command) " ")))
+    (mapconcat 'prin1-to-string (apply (car extended-command)
+                                       (cdr extended-command)) " ")))
 
 (defun svg-path (svg commands &rest args)
   "Add the outline of a shape to SVG according to COMMANDS.
diff --git a/src/eval.c b/src/eval.c
index 014905ce6d..1b9fd90482 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2358,7 +2358,7 @@ eval_sub (Lisp_Object form)
   return val;
 }
 \f
-DEFUN ("apply", Fapply, Sapply, 1, MANY, 0,
+DEFUN ("apply", Fapply, Sapply, 2, MANY, 0,
        doc: /* Call FUNCTION with our remaining args, using our last arg as list of args.
 Then return the value FUNCTION returns.
 Thus, (apply \\='+ 1 2 \\='(3 4)) returns 10.
-- 
2.26.2