Re: How to delete a created Glissando without impact on line break?

Am So., 28. Juni 2026 um 14:46 Uhr schrieb Dan Eble <[email protected]>:
>
> On 2026-06-28 07:43, Thomas Morley wrote:
> > currently I'm looking at
> > https://gitlab.com/lilypond/lilypond/-/work_items/6946 "glissando and
> > line break issue".
>
> The following analysis is from the LLM [Qwen
> 3.6](https://huggingface.co/Jundot/Qwen3.6-27B-oQ4-mtp).  It seems
> reasonable to me -- a nice change from the usual! -- but I leave it to
> you to verify.
> --
> Dan
>
> ---
>
> **Root cause confirmed.** The bug is in `Spanner_break_forbid_engraver`,
> specifically a combination of two issues:
>
> ### 1. `Grob::suicide()` clears interfaces (`grob.cc:338`)
>
> ```cpp
> interfaces_ =3D SCM_EOL;
> ```
>
> This destroys the grob's interface list, which is needed for dispatch
> lookup.
>
> ### 2. `acknowledge_grobs()` queries the grob's interfaces at dispatch
> time (`engraver-group.cc:146`)
>
> ```cpp
> SCM ifaces =3D info.grob ()->interfaces ();
> acklist =3D Engraver_dispatch_list::create (get_simple_trans_list (),
>                                            ifaces, info.start_end ());
> ```
>
> When the grob has been suicided, `interfaces()` returns `SCM_EOL`. The
> dispatch list creation iterates over an empty interface list, finds no
> acknowledgers, and returns `SCM_EOL`. The
> `acknowledge_end_unbreakable_spanner` callback is **never called**.
>
> ### 3. `Spanner_break_forbid_engraver` never cleans up dead grobs
>
> The engraver stores raw `Spanner*` pointers in `running_spanners_`. The
> only removal path is `acknowledge_end_unbreakable_spanner` (line 49-56),
> which now never fires for suicided grobs. The pointer stays in the
> vector forever.
>
> `pre_process_music()` (line 42-46) checks `running_spanners_.size()` =E2=
=80=94
> it's always > 0 =E2=80=94 so `forbidBreak` is permanently set to `SCM_BOO=
L_T`.
>
> ---

LLM's analysis is pure C++-stuff, out of my paygrade...