Re: [RFC] Automatic 'make check' in CI

[Jonas Hahnfeld]

Am Sonntag, den 22.11.2020, 22:49 +0100 schrieb David Kastrup:
> Jonas Hahnfeld <hahnjo@hahnjo.de> writes:
> 
> > Nope, that was a red herring: The reason is that the footnote creation
> > process in footnote-volta-spanner.ly messes with (point-stencil), which
> > is used by skyline-point-extent.ly and also the BendSpanner. As far as
> > I understand the Stencil class, its objects are not immutable...
> > 
> > One of the following two changes fixes the problem in my local test
> > scenario:
> > 
> > [...]
> > 
> > My gut feeling is that we should fix null-markup because nothing should
> > ever translate / rotate / modify the global point-stencil, thoughts?
> 
> To me that seems crazy.  Instead \footnote should not modify the stencil
> generated from its argument in place.  If it needs something with
> different dimensions, it needs to create a new stencil, copying the
> stencil expression and changing the dimensions.

Yes indeed, this seems to be the contract for stencils: Make a copy
whenever a Stencil is passed in from Scheme. I managed to find the code
path for Balloon grobs that violate this rule, here's a fix:
https://gitlab.com/lilypond/lilypond/-/merge_requests/522
(Note that the test case shows that this was already broken before this
unstable series, at least 2.20.0 but probably older versions too).

If possible, I'd like to merge this rather sooner than later so I can
finally post the MR to enable 'make check'...

> ly:stencil-set-extent! has been removed in 2.5.17.  Extents are not
> intended to be mutable as far as I can discern, so if our C++ code does
> violate that assumption, it is that code we should fix instead of giving
> up on behavior guaranteed from the Scheme side of things.

In fact, the C++ code does and many methods of the Stencil class modify
the object, but this is ok as long as we stick to the rule above. I'd
be happy to assert in some way that stencil representations coming from
Scheme are not altered, but I can't think of a good way to do this...

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