engraver: continue when trying to create non-existent Grob

engraver: continue when trying to create non-existent Grob

[dak, 2020-02-10 21:31:46]

https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc
File lily/engraver.cc (right):

https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc#newc...
lily/engraver.cc:126: grob = new Item (SCM_EOL);
Ugh.  How is that going to work?  I am not sure we aren't better off with a hard
exit.  Admittedly, a failed assertion makes little sense after a
programming_error: this should have been a hard error in the first place.

What is the use case?

[hanwenn, 2020-02-10 21:35:30]

On 2020/02/10 21:31:46, dak wrote:
> https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc
> File lily/engraver.cc (right):
> 
>
https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc#newc...
> lily/engraver.cc:126: grob = new Item (SCM_EOL);
> Ugh.  How is that going to work?  I am not sure we aren't better off with a
hard
> exit.  Admittedly, a failed assertion makes little sense after a
> programming_error: this should have been a hard error in the first place.
> 
> What is the use case?

Without this, you get a segfault because we take a cdr of an empty list.

[dak, 2020-02-10 21:40:03]

On 2020/02/10 21:35:30, hanwenn wrote:
> On 2020/02/10 21:31:46, dak wrote:
> > https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc
> > File lily/engraver.cc (right):
> > 
> >
>
https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc#newc...
> > lily/engraver.cc:126: grob = new Item (SCM_EOL);
> > Ugh.  How is that going to work?  I am not sure we aren't better off with a
> hard
> > exit.  Admittedly, a failed assertion makes little sense after a
> > programming_error: this should have been a hard error in the first place.
> > 
> > What is the use case?
> 
> Without this, you get a segfault because we take a cdr of an empty list.

Ugh.  Ok, that's rather awful.  But don't we run into followup errors with that
make_item (SCM_EOL) ?

[hanwenn, 2020-02-10 21:41:36]

On 2020/02/10 21:40:03, dak wrote:
> On 2020/02/10 21:35:30, hanwenn wrote:
> > On 2020/02/10 21:31:46, dak wrote:
> > > https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc
> > > File lily/engraver.cc (right):
> > > 
> > >
> >
>
https://codereview.appspot.com/547620043/diff/545560043/lily/engraver.cc#newc...
> > > lily/engraver.cc:126: grob = new Item (SCM_EOL);
> > > Ugh.  How is that going to work?  I am not sure we aren't better off with
a
> > hard
> > > exit.  Admittedly, a failed assertion makes little sense after a
> > > programming_error: this should have been a hard error in the first place.
> > > 
> > > What is the use case?
> > 
> > Without this, you get a segfault because we take a cdr of an empty list.
> 
> Ugh.  Ok, that's rather awful.  But don't we run into followup errors with
that
> make_item (SCM_EOL) ?

apparently, no. 

it doesn't print anything obviously.

[hanwenn, 2020-02-19 09:35:32]

commit c3cb10296708a2efcdac03d02507c9b55e3aa42c
Author: Han-Wen Nienhuys <hanwen@lilypond.org>
Date:   Mon Feb 10 22:12:41 2020 +0100

    engraver: continue when trying to create non-existent Grob
    
    https://sourceforge.net/p/testlilyissues/issues/5748
    http://codereview.appspot.com/547620043