bug#39190: 28.0.50; two buffers with same buffer-file-name (diff-syntax-fontify-props)

[Stefan Monnier]

> Maybe a simpler variant would be to use some other variable to distinguish
> sub-mode and its parent, instead of relying on delay-mode-hooks?

That's kinda hard if you want to use define-derived-mode and we do: when
we call `conf-foo-mode` the first things it does is: bind
`delay-mode-hooks` and call the parent (`conf-mode`), so the only
difference between this call to the parent and a direct call to the
generic entry point is the binding of `delay-mode-hooks`.


        Stefan