I've tried to approach this systematically and made the observation that the
moving dots might be related to what other regression tests are built for
`check` (and maybe in what order? not sure if that is stable across
invocations). Based on that, I've created a small set of input files (see
attached archive) that really changes at random on subsequent invocations of
`lilypond -dread-file-list names.ly`, at least on my system.
I went on to understand what is causing the non-determinism. From what I found
so far, it looks like some functions might be called in a different order in
subsequent invocations of lilypond. I've also put a small diff into above
archive which adds a few `printf`s: Sometimes
`Dot_column::calc_positioning_done` is called before
`Rest_collision::force_shift_callback_rest`, on another invocation it might be
the other way around. The problem is that
`Rest_collision::force_shift_callback_rest` calls `Grob::translate_axis` which
updates a cache and changes the Y position.
At least that's what it looks like to me right now, without knowing which
ordering of above functions would be correct. But a changing order at random
seems odd, doesn't it? Posting here in case somebody with more experience goes
like "hey, that can be easily fixed like this". Otherwise I'll try to
understand what's causing the different orders and how it can be turned off.
Attachments:
-
[rest-dot-positions.zip](https://sourceforge.net/p/testlilyissues/issues/_discuss/thread/d945be2d/b84f/attachment/rest-dot-positions.zip)
(1.5 kB; application/zip)
---
** [issues:#5217] random results for the merge-rests-engraver regression test**
**Status:** New
**Created:** Fri Oct 20, 2017 07:28 AM UTC by Knut Petersen
**Last Updated:** Fri Nov 01, 2019 02:45 PM UTC
**Owner:** Knut Petersen
**Attachments:**
-
[out-test-baseline-merge-rests-engraver.png](https://sourceforge.net/p/testlilyissues/issues/5217/attachment/out-test-baseline-merge-rests-engraver.png)
(23.8 kB; image/png)
-
[out-test-merge-rests-engraver.png](https://sourceforge.net/p/testlilyissues/issues/5217/attachment/out-test-merge-rests-engraver.png)
(23.7 kB; image/png)
There is some randomness in the placement of dots. The merge-rests-engraver.ly
regtest (git-version557dc7) exposes the problem as the output might be one of
the two attached pngs. The probability for both results is identical on my
system.
---
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