Warn when building with a table of contents which is going to have a red warning

[adamtheturtle]

I recently converted documentation for multiple projects to use the Furo theme.
I did not want to see the red warning box around .. contents blocks.
I had to either remove these blocks or use :class: this-will-duplicate-information-and-it-is-still-useful-here.

It would have been useful when doing this task if there had been a build-time warning that my documentation was going to have a nasty red box.

[pradyunsg]

Hmm! This is an interesting idea, but this would be non-trivial to implement; which is why I think this isn't worthwhile.

While this would certainly be a nice quality-of-life improvement for documentation authors porting the documentation, I don't think the maintenance overhead of overriding a provided-by-default sphinx directive would justify that benefit.

[adamtheturtle]

Understood - I am not familiar with that maintenance burden and I'll of course trust you on what is "worthwhile".

One thought: Perhaps it would be useful to document this effect of switching documentation to use Furo somewhere clear in Furo's documentation.

[pradyunsg]

I think it's fine as is, TBH.

I don't think anyone would switch their documentation theme without checking that a reasonable chunk of their pages look OK. And, the warning in the output is clear enough and provides clear actionable steps.