On 1/7/20 6:16 AM, Stefan Monnier wrote:
> I'd be in
> favor of introducing this backward incompatibility in Emacs-28, unless
> we can find a good use case where the structural-equality is needed
> for them.

I looked for use cases within Emacs, and found only one: a test case 
that I changed to use compare-window-configurations instead. I don't 
think this was a good use case; it's just a hack in a test.

I agree with Martin that comparing window configurations is something of 
a botch. Despite some documentation to the contrary, neither 'equal' nor 
compare-window-configurations compares all components of window 
configurations (though the two functions do compare different sets of 
components). If there's a solid need for comparing different sets of 
components of window configurations (and I doubt whether the test case 
establishes a need), it could be implemented by adding an argument to 
compare-window-configurations to say how to do the comparison. However, 
there doesn't seem to be a significant need to make all this part of 
'equal'.

So, after writing some sxhash-equal test cases and then fixing Emacs to 
handle these test cases properly, I boldly installed the attached patch 
into master. This should make sxhash-equal compatible with 'equal'. 
Comments welcome as usual.