[Lilypond-auto] [LilyIssues-auto] [testlilyissues:issues] #5217 random results for the merge-rests-engraver regression test

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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 printfs: 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 (1.5 kB; application/zip)

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[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 (23.8 kB; image/png)
• 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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