* lisp/minibuffer.el (completion-at-point): Emit warning for ill-behaved

completion functions.

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 003018d88d7a6626755788afc2de342f56c3d79c..31e4e9d10f86872aea8fabed8ecfe72fed47cf62 100644 (file)
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2014-09-30  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+       * minibuffer.el (completion-at-point): Emit warning for ill-behaved
+       completion functions.
+
 2014-09-29  Stefan Monnier  <monnier@iro.umontreal.ca>
 
        * ses.el (ses--letref): Quote value before it gets re-evaluated.

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index f998843cd854412db1adb22797c79671793a4f2a..fb74af2e0df3a165d65abf4fcaa4a351ac7cbcd3 100644 (file)
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -2106,7 +2106,11 @@ The completion method is determined by `completion-at-point-functions'."
          (completion-in-region start end collection
                                (plist-get plist :predicate))))
       ;; Maybe completion already happened and the function returned t.
-      (_ (cdr res)))))
+      (_
+       (when (cdr res)
+         (message "Warning: %S failed to return valid completion data!"
+                  (car res)))
+       (cdr res)))))
 
 (defun completion-help-at-point ()
   "Display the completions on the text around point.