Markus Triska <markus.triska at gmx.at>

(byte-compile-normal-call): Warn when `mapcar' is called for effect.

1 files changed, 4 insertions, 0 deletions

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 2c14bb66609..10b65d4c47e 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -2831,6 +2831,10 @@ That command is designed for interactive use only" fn))
 (defun byte-compile-normal-call (form)
   (if byte-compile-generate-call-tree
       (byte-compile-annotate-call-tree form))
+  (when (and for-effect (eq (car form) 'mapcar))
+    (byte-compile-set-symbol-position 'mapcar)
+    (byte-compile-warn
+     "`mapcar' called for effect; use `mapc' or `dolist' instead"))
   (byte-compile-push-constant (car form))
   (mapc 'byte-compile-form (cdr form))	; wasteful, but faster.
   (byte-compile-out 'byte-call (length (cdr form))))