GNU bug report logs - #17234
24.3.50; overlay priority : cons cells make an error in ediff

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From: Glenn Morris <rgm <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 17234 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: bug#17234: 24.3.50; overlay priority : cons cells make an error in ediff
Date: Fri, 11 Apr 2014 12:31:48 -0400

Stefan Monnier wrote:

> It has always been the case that `priority' could be any value.

But the only documented values were and are nil and positive integers.
I really doubt anyone was intentionally using anything else to mean "nil".

> Any non-number value was treated as nil by the display engine, whereas
> now some cons values are treated as something else.

So even if your previous point was correct, it's still an incompatible
change. A cons cell can no longer be used to mean "no explicit priority".

> But ediff's bug could already be triggered in Emacs<24.4 by a package
> installing an overlay with a `priority' that's a cons cell.

Since we never (?) had any such reports, I conclude nobody did that.

But I imagine ediff was not the only package trying to get the priority
of an overlay and do something with the answer (however misguided you
think that might be).

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