bug#37774: 27.0.50; new :extend attribute broke visuals of all themes and other packages

[Dmitry Gutov]

On 08.12.2019 17:50, Eli Zaretskii wrote:

> Experience teaches up that quite a few problems, especially in subtle
> areas, are discovered only after the release.  I guess it means that
> the group of people who use the pretest is not representative enough.

Sure. But on the other hand, the number of users in the period before 
the pretest in even smaller.

> OK, I've now reviewed all the callers of face-spec-recalc, and all of
> its callers' callers, and wrote a bunch of tests to make sure that we
> don't break anything (or at least anything important).

Thank you. That's pretty comprehensive. I would suggest to install those 
tests, but I wonder how they would interact with a long-running test 
session.

Running them in an interactive session was tricky as well because 
visiting any file, even in 'emacs -Q', automatically leads to 
diff-mode.el being loaded, and so (should-not (featurep 'diff-mode)) 
fails right away.

They also rely on the existing themes, the definitions of which will change.

> The tests in
> the patch below all pass for the current code on master, and include a
> couple of comments where the changes to implicitly inherit :extend by
> themes are supposed to change the expected result.  If after applying
> your patch all the tests still pass, both in -batch and in an
> interactive session, then I think we are good to go (after adding the
> necessary documentation and NEWS entry).

They do! If by "still pass" you mean the version of these tests where 
the expected values are replaced with the values from "should be" comments.

All right, how does the attached patch look?

In addition to it, I'd like to revert the part of 64687872f6 that 
changed the bundled themed (etc/themes/*). Is that okay?

inherit-face-extend-spec-4.diff
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