Subject: bug#35767: 26.1; byte compiler lost warning about calling define-key with wrong number of arguments

From: Noam Postavsky <[email-masked]>
Date: Mon, 27 May 2019 20:59:30 -0400

tags 35767 + patch
quit

Alex Branham <[email-masked]> writes:

> (define-key "l" #'ignore)
>
> Then call:
>
> emacs -Q --eval "(setq byte-compile-error-on-warn t)" -batch -f batch-byte-compile foo.el
>
> it _should_ emit an error since define-key gets called with the wrong
> number of arguments. In Emacs 25.3, it does. In Emacs 26.1 and Emacs
> built recently from git master, it does not.

Specifically, Emacs 26+ doesn't warn about wrong number of arguments to
subrs.  The fix seems simple enough to apply to emacs-26.

Minor caveat, some subrs (e.g., length) get warned about twice (with
slightly different wording each time), but this occurs in 25.3 as well,
so I guess it's acceptable:

    Warning: ‘length’ called with 3 args, but requires 1
    Warning: length called with 3 arguments, but accepts only 1

>From 050b2bd3041d3d856dcb5ff6adfa75e8a63d8032 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <[email-masked]>
Date: Mon, 27 May 2019 20:36:41 -0400
Subject: [PATCH] Warn about wrong number of args for subrs (Bug#35767)

* lisp/emacs-lisp/bytecomp.el (byte-compile-callargs-warn): Don't
assume byte-compile-fdefinition will return non-nil.
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-warn-wrong-args)
(bytecomp-warn-wrong-args-subr): New tests.
---
 lisp/emacs-lisp/bytecomp.el            |  2 +-
 test/lisp/emacs-lisp/bytecomp-tests.el | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 9ea4179b68..72e81a653c 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -1379,7 +1379,7 @@ (defun byte-compile-function-warn (f nargs def)
 (defun byte-compile-callargs-warn (form)
   (let* ((def (or (byte-compile-fdefinition (car form) nil)
 		  (byte-compile-fdefinition (car form) t)))
-	 (sig (byte-compile--function-signature def))
+         (sig (byte-compile--function-signature (or def (car form))))
 	 (ncall (length (cdr form))))
     ;; Check many or unevalled from subr-arity.
     (if (and (cdr-safe sig)
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el b/test/lisp/emacs-lisp/bytecomp-tests.el
index bc28c5a6a0..c399f65b40 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -438,6 +438,20 @@ (ert-deftest bytecomp-tests--warnings ()
     ;; Should not warn that mt--test2 is not known to be defined.
     (should-not (re-search-forward "my--test2" nil t))))
 
+(ert-deftest bytecomp-warn-wrong-args ()
+  (with-current-buffer (get-buffer-create "*Compile-Log*")
+    (let ((inhibit-read-only t)) (erase-buffer))
+    (byte-compile '(remq 1 2 3))
+    (ert-info ((buffer-string) :prefix "buffer: ")
+      (should (re-search-forward "remq.*3.*2")))))
+
+(ert-deftest bytecomp-warn-wrong-args-subr ()
+  (with-current-buffer (get-buffer-create "*Compile-Log*")
+    (let ((inhibit-read-only t)) (erase-buffer))
+    (byte-compile '(safe-length 1 2 3))
+    (ert-info ((buffer-string) :prefix "buffer: ")
+      (should (re-search-forward "safe-length.*3.*1")))))
+
 (ert-deftest test-eager-load-macro-expansion ()
   (test-byte-comp-compile-and-load nil
     '(progn (defmacro abc (arg) 1) (defun def () (abc 2))))
-- 
2.11.0