Round-trip extraChartSongFields / unrecognizedSyncTrackEvents / unrecognizedEventsTrackMidiEvents - #87
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April 21, 2026 23:20
…ognizedEventsTrackMidiEvents
The parser preserves three post-writer-stack round-trip buckets that the
writers weren't yet emitting:
- `metadata.extraChartSongFields` (unknown `[Song]` keys, .chart source)
- `unrecognizedSyncTrackEvents` (non-B/TS `[SyncTrack]` lines, .chart)
- `unrecognizedEventsTrackMidiEvents` (non-text MIDI events on the EVENTS
track — e.g. RB practice-mode
assist-sample notes 24/25/26)
Emit them:
- `writeChartFile` appends `extraChartSongFields` at the tail of `[Song]`
(values written verbatim — no quoting added or stripped). Editors and
consumers should treat these as opaque and never synthesize them; this
is strictly a round-trip aid for tools like Moonscraper that author
deprecated fields (`Player2`, `HoPo`, `PreviewEnd`, audio-stream
filenames, etc.). Any audio file discovery should go through folder
scan, not via `[Song].*Stream` values.
- `writeChartFile` emits `unrecognizedSyncTrackEvents` alongside tempos +
time signatures in `[SyncTrack]`, sorted by tick (TS < B < raw at the
same tick for determinism). Text is written verbatim as
`${tick} = ${text}`, so tempo anchors (`A <microseconds>`) and any
future SyncTrack event types survive a parse → write loop without
parser updates.
- `writeMidiFile` appends `unrecognizedEventsTrackMidiEvents` to the
EVENTS track after sections / end events / unrecognized text events /
coda. Events arrive with absolute-tick `deltaTime` (scan-chart's
post-process) and get re-deltified by `finalizeMidiTrack`.
`.chart`-only fields (`extraChartSongFields`, `unrecognizedSyncTrackEvents`)
are dropped when writing to `.mid`, and `unrecognizedEventsTrackMidiEvents`
is dropped when writing to `.chart` — tests pin both contracts so a future
writer change doesn't accidentally smuggle them through as something else.
11 new tests in `round-trip-unrecognized-extras.test.ts` cover legacy-field
preservation, tempo-anchor round-trip, forward-compat for unknown SyncTrack
types, co-occurrence with tempos/TS at the same tick, practice-assist note
round-trip on `.mid`, and the cross-format drop contracts. All 1020 tests
pass (1009 existing + 11 new).
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The parser preserves three post-writer-stack round-trip buckets that the
writers weren't yet emitting:
metadata.extraChartSongFields(unknown[Song]keys, .chart source)unrecognizedSyncTrackEvents(non-B/TS[SyncTrack]lines, .chart)unrecognizedEventsTrackMidiEvents(non-text MIDI events on the EVENTStrack — e.g. RB practice-mode
assist-sample notes 24/25/26)
Emit them:
writeChartFileappendsextraChartSongFieldsat the tail of[Song](values written verbatim — no quoting added or stripped). Editors and
consumers should treat these as opaque and never synthesize them; this
is strictly a round-trip aid for tools like Moonscraper that author
deprecated fields (
Player2,HoPo,PreviewEnd, audio-streamfilenames, etc.). Any audio file discovery should go through folder
scan, not via
[Song].*Streamvalues.writeChartFileemitsunrecognizedSyncTrackEventsalongside tempos +time signatures in
[SyncTrack], sorted by tick (TS < B < raw at thesame tick for determinism). Text is written verbatim as
${tick} = ${text}, so tempo anchors (A <microseconds>) and anyfuture SyncTrack event types survive a parse → write loop without
parser updates.
writeMidiFileappendsunrecognizedEventsTrackMidiEventsto theEVENTS track after sections / end events / unrecognized text events /
coda. Events arrive with absolute-tick
deltaTime(scan-chart'spost-process) and get re-deltified by
finalizeMidiTrack..chart-only fields (extraChartSongFields,unrecognizedSyncTrackEvents)are dropped when writing to
.mid, andunrecognizedEventsTrackMidiEventsis dropped when writing to
.chart— tests pin both contracts so a futurewriter change doesn't accidentally smuggle them through as something else.
11 new tests in
round-trip-unrecognized-extras.test.tscover legacy-fieldpreservation, tempo-anchor round-trip, forward-compat for unknown SyncTrack
types, co-occurrence with tempos/TS at the same tick, practice-assist note
round-trip on
.mid, and the cross-format drop contracts. All 1020 testspass (1009 existing + 11 new).