Allow melismas across rests and fix lyrics crashes

[ajuncosa]

Resolves: #33735
Resolves: #34027
Resolves: #31986

In this PR:

• Allow melismas across rests

• Add a parameter to prevent UndoableTransaction::unwind from immediately freeing the text element. This was causing crashes that affected, at least, the creation of empty lyrics and introduction of melismas, rendering them nearly unusable. The crashes were due to:

  1. double frees because the TextBase::endEdit was deferring deletion through deleteLater()
  2. the elements were being referenced in multiple places after the AddElement::cleanup had freed them (during unwind).

  Therefore, the most straightforward solution to avoid changing the current logic seemed to be to make the cleanup optional. There is probably a cleaner and more future-proof solution to this, but at least it solves the crashes for the time being.

• Fix buggy vertical positioning of lyrics syllables on partial re-layout

• Drop empty lyrics on file read: our lyrics system assumes there will be no empty lyrics in the mscx file, therefore any pre-existing empty lyrics are deleted through the newly added lyrics path (in TextBase::endEdit), causing later crashes.

  • Note: this situation should not be possible with 5.0 scores, but mscx files generated using previous versions could end up with empty text fields (e.g. when the lyrics contained only line breaks, because they were not escaped into <br/>). So the fix just acts as a sanity check.

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📝 Walkthrough

Walkthrough

A keepRolledBackElements boolean is threaded through UndoableTransaction::unwind, TransactionManager::endTransaction, and Score::endCmd. Rollback now skips cleanup when that flag is set, letting rolled-back elements remain for deferred deletion in TextBase::endEdit. The lyrics empty-text path now triggers relayout through prev->triggerLayout() and score()->update(). Lyrics::adjustPrevious(), NotationInteraction::addMelisma, and segmentsAreAdjacent also update their gating and lookup logic.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant TextBase
  participant Score
  participant TransactionManager
  participant UndoableTransaction
  TextBase->>Score: endCmd(true, false, true)
  Score->>TransactionManager: endTransaction(true, false, true)
  TransactionManager->>UndoableTransaction: unwind(false)
  UndoableTransaction-->>TransactionManager: rollback without cleanup
  TransactionManager-->>Score: return
  Score-->>TextBase: continue deferred deletion

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🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	⚠️ Warning	The description includes issue resolution and a summary, but it omits the required template checklist and several required confirmations.	Add the template checklist items and required confirmations for CLA, testing, commit messages, coding rules, and prior attempts.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The melisma scan change and the unwind cleanup parameter directly address #33735 and #34027.
Out of Scope Changes check	✅ Passed	The other edits appear to support the melisma and crash fixes, with no clearly unrelated scope added.
Title check	✅ Passed	The title clearly summarizes the main feature and crash-fix changes in the PR.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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🔥 Problems

Linked repositories: Public OSS repositories can only analyze public repositories installed in this organization. No linked repositories were analyzed; skipped musescore/muse_framework.git.

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[davidstephengrant]

@ajuncosa When closing the input field after creating extenders, the syllable may jump to an incorrect vertical position. This corrects itself upon relayout.

Screen.Recording.2026-07-03.at.11.16.28.mov

[denisfalqueto]

I built this PR locally on Linux (Qt, Debug) and manually tested the lyrics fixes:

• Creating an empty lyrics syllable and leaving it without typing anything (the crash I reported in Crash (use-after-free/double-free) when leaving an empty lyrics syllable with Shift+Space #34131) no longer crashes. ✅
• Entering lyrics on a note followed by a rest and extending a melisma (_) across the rest works as expected, with no crash. ✅

Both scenarios that previously reproduced the problems now behave correctly. Thanks for the fix!

[mercuree]

This PR also partially fixes #31986. The second case with the project file from Musescore 4.6.5 still crashes.