From: Alan Mackenzie <acm@muc.de>
To: emacs-devel@gnu.org
Subject: setq's with missing final arguments.
Date: Sun, 22 Nov 2015 12:26:57 +0000 [thread overview]
Message-ID: <20151122122657.GA2332@acm.fritz.box> (raw)
Hello, Emacs.
Consider this file:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defvar foo t)
(defvar bar t)
(defun bad-setq ()
"Doc string"
(setq foo 5
bar))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
In the setq, there is a missing argument after "bar". At the moment,
the byte compiler just generates code to assign nil to bar, without
giving any warning. IMAO, this is Very Bad.
I propose to insert code into the byte compiler to detect and warn of
this scenario:
diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 3574364..1e75d48 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -3739,7 +3739,11 @@ byte-compile-setq
(let ((args (cdr form)))
(if args
(while args
- (byte-compile-form (car (cdr args)))
+ (if (eq (length args) 1)
+ (byte-compile-warn
+ "implicit nil assignment to `%s'"
+ (prin1-to-string (car args))))
+ (byte-compile-form (car (cdr args)))
(or byte-compile--for-effect (cdr (cdr args))
(byte-compile-out 'byte-dup 0))
(byte-compile-variable-set (car args))
Any objections?
Just as a matter of interest, I came across an actual instance of this
solecism in Emacs, where it is clearly an error. For some reason, this
instance doesn't trigger an "implicit nil assignment" warning; perhaps
it is because it is inside a pcase.
--
Alan Mackenzie (Nuremberg, Germany).
next reply other threads:[~2015-11-22 12:26 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-22 12:26 Alan Mackenzie [this message]
2015-11-22 12:31 ` setq's with missing final arguments David Kastrup
2015-11-22 12:35 ` Oleh Krehel
2015-11-22 12:44 ` Teemu Likonen
2015-11-22 15:53 ` multi-assignment setq [was: setq's with missing final arguments.] Drew Adams
2015-11-23 7:58 ` Oleh Krehel
2015-11-23 15:02 ` Drew Adams
2015-11-22 12:52 ` setq's with missing final arguments Andreas Schwab
2015-11-22 13:03 ` Artur Malabarba
2015-11-22 13:08 ` David Kastrup
2015-11-22 13:11 ` Andreas Schwab
2015-11-22 13:23 ` David Kastrup
2015-11-22 13:34 ` Andreas Schwab
2015-11-22 14:10 ` Alan Mackenzie
2015-11-22 15:44 ` Eli Zaretskii
2015-11-22 19:44 ` Alan Mackenzie
2015-11-23 1:36 ` Drew Adams
2015-11-22 15:42 ` Johan Bockgård
2015-11-22 16:04 ` Drew Adams
2015-11-22 15:52 ` Drew Adams
2015-11-22 23:08 ` Alan Mackenzie
2015-11-22 23:20 ` John Wiegley
2015-11-23 1:54 ` Drew Adams
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20151122122657.GA2332@acm.fritz.box \
--to=acm@muc.de \
--cc=emacs-devel@gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.savannah.gnu.org/cgit/emacs.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).