bug#39971: 28.0.50; Behavior change in flymake-diagnostic-beg/end

[João Távora]

Philipp Stephani <p.stephani2@gmail.com> writes:

> This was introduced in commit 5b48dab412c61980bca63a67a5d548d07e56b404.
> While the intention of that commit is good, I'm not sure we should make
> such a breaking change.

Programs relying on that behaviour were broken anyway.  Do you have
non-synthetic example?

But even in Emacs 26.3, the new version of Flymake can be (and usually
is) upgradeable with M-x install-package.

> Basically, the flymake-diagnostic type no longer behaves like an
> ordinary struct.

It doesn't have to, and that's good.  It means we can hide the
implementation.  If you can come up with a simple enough doc fix that
expresses that flymake-diagnostic-beg/end can only be invoked on
diagnostics that have been reported to Flymake, I'll merge it.

Also, we can make the error message a bit friendlier to express that
fact, so maybe include that in your patch?

João