Re: Standardizes use of empty extents in pure heights and skylines. (issue 7310075)

[dak]

https://codereview.appspot.com/7310075/diff/53001/input/regression/skyline-point-extent.ly
File input/regression/skyline-point-extent.ly (right):

https://codereview.appspot.com/7310075/diff/53001/input/regression/skyline-point-extent.ly#newcode5
input/regression/skyline-point-extent.ly:5: even though the
@code{NoteHead} stencils are empty. The @code{Stem_engraver}
This talks about the NoteHead stencil being empty, but the actual code
uses a point-stencil (which is _not_ empty).

https://codereview.appspot.com/7310075/diff/53001/lily/separation-item.cc
File lily/separation-item.cc (right):

https://codereview.appspot.com/7310075/diff/53001/lily/separation-item.cc#newcode148
lily/separation-item.cc:148: Interval extra_width = robust_scm2interval
(elts[i]->get_property ("extra-spacing-width"),
This is not related to this patch, but isn't it complete nonsense to use
an Interval here rather than a Drul_array or other form of offset pair?

The LEFT and RIGHT values don't form an interval as far as I can see.

https://codereview.appspot.com/7310075/diff/53001/lily/skyline.cc
File lily/skyline.cc (right):

https://codereview.appspot.com/7310075/diff/53001/lily/skyline.cc#newcode649
lily/skyline.cc:649: return ret;
Why not just
return *this;
here?  The function does not return a reference, so a copy is
constructed anyway.  There is no point in doing yet another copy, is
there?

https://codereview.appspot.com/7310075/diff/53001/scm/output-lib.scm
File scm/output-lib.scm (right):

https://codereview.appspot.com/7310075/diff/53001/scm/output-lib.scm#newcode472
scm/output-lib.scm:472: 10000000))
Don't we have some constants for the full range START and END values?

https://codereview.appspot.com/7310075/diff/53001/scm/output-lib.scm#newcode478
scm/output-lib.scm:478: (define-public
pure-from-neighbor-interface::unobtrusive-height
"unobtrusive" is a bit obscure: I suspected the only-a-bit-empty
interval at first.  "height-if-pure" would be quite more descriptive.

https://codereview.appspot.com/7310075/