Subject: Re: bug#67008: 30.0.50; Multiple major mode parents

From: Mattias Engdegård <[email-masked]>
Date: Fri, 17 Nov 2023 15:04:24 +0100

> Garbage in, garbage out, eh?

Indeed. Let's document the constraint on the argument and, if it's not too expensive, verify.

>> or if the default error function (caar) is used.
> 
> Same.

Well sort of -- since it's the default error function, we must be able to defend the results of having it used.
Otherwise we're just saying 'if the input graph is cyclic then the output is undefined' but that clearly isn't true since we make an effort to return something semi-useful in that case.

Are the duplicates essential to proper functioning of `cl--class-allparents` and `derived-mode-all-parents`, or would they work just as well with some edge of the cycle removed instead?