writeChartFile: re-quote extraChartSongFields per .chart spec types

src/__tests__/chart-round-trip-extras.test.ts

@@ -67,7 +67,8 @@ describe('.chart [Song] unknown-key preservation (metadata.extraChartSongFields)
 		// Known typed fields still populate.
 		expect(r.metadata.name).toBe('Test')
 		expect(r.metadata.artist).toBe('Me')
-		// Everything else lands in the preservation bag, values unchanged.
+		// Everything else lands in the preservation bag, with quotes stripped.
+		// The writer re-applies quoting per the spec's field-type table on emit.
 		expect(r.metadata.extraChartSongFields).toEqual({
 			Player2: 'bass',
 			PreviewEnd: '0',

src/__tests__/round-trip-unrecognized-extras.test.ts

@@ -63,22 +63,77 @@ describe('writeChartFile round-trip: metadata.extraChartSongFields', () => {
 		})
 	})
 
-	it('preserves quoted string values including inner spaces', () => {
+	it('round-trips bare values cleanly (writer re-quotes per spec)', () => {
+		// The parser strips enclosing quotes on read, so values stored in
+		// `extraChartSongFields` are always bare. The writer re-applies quoting
+		// from the spec's field-type table, so a bare-then-quoted-then-stripped
+		// trip is lossless for the value content.
 		const chart = createEmptyChart({ format: 'chart' })
 		chart.metadata.extraChartSongFields = {
-			ArtistText: '"by"',
-			MusicStream: '"Some Song.ogg"',
+			ArtistText: 'by',
+			MusicStream: 'Some Song.ogg',
 		}
 		const re = roundTripChart(chart)
 		expect(re.metadata.extraChartSongFields).toEqual({
-			// The parser strips one layer of enclosing quotes on read. What matters
-			// is that the key survives and the value round-trips: re-writing the
-			// stripped form re-adds no quotes, so the next parse sees it unquoted.
 			ArtistText: 'by',
 			MusicStream: 'Some Song.ogg',
 		})
 	})
 
+	it('emits MusicStream with the quotes Moonscraper expects', () => {
+		// Pin the on-disk shape directly: re-writing must produce
+		// `MusicStream = "song.ogg"` (quoted), not `MusicStream = song.ogg`.
+		// Bare value in → quoted value out.
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.metadata.extraChartSongFields = { MusicStream: 'song.ogg' }
+		const text = writeChartFile(chart)
+		expect(text).toContain('MusicStream = "song.ogg"')
+		expect(text).not.toMatch(/MusicStream = song\.ogg[^"]/)
+	})
+
+	it('emits Player2 unquoted (bare-string field per spec)', () => {
+		// `Player2` is the lone `bare string` type in the [Song] section. The
+		// writer must NOT quote it, even though it's a string-y value.
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.metadata.extraChartSongFields = { Player2: 'bass' }
+		const text = writeChartFile(chart)
+		expect(text).toContain('Player2 = bass')
+		expect(text).not.toContain('Player2 = "bass"')
+	})
+
+	it('emits numeric-typed legacy fields unquoted', () => {
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.metadata.extraChartSongFields = { HoPo: '0', PreviewEnd: '180' }
+		const text = writeChartFile(chart)
+		expect(text).toContain('HoPo = 0')
+		expect(text).toContain('PreviewEnd = 180')
+		expect(text).not.toContain('HoPo = "0"')
+	})
+
+	it('quotes unknown string-shaped keys, leaves primitive-shaped keys bare', () => {
+		// Forward-compat heuristic for keys outside the spec table: if the
+		// value looks like a primitive literal (number / decimal / boolean),
+		// emit bare; otherwise quote. Erring on the side of quoting matches
+		// what readers (Moonscraper, scan-chart) accept and what authoring
+		// tools mostly emit. The boolean case mirrors `OriginalArtist = false`
+		// observed in the corpus.
+		const chart = createEmptyChart({ format: 'chart' })
+		chart.metadata.extraChartSongFields = {
+			MysteryString: 'hello',
+			MysteryNumber: '42',
+			MysteryDecimal: '-1.5',
+			MysteryBool: 'false',
+			OriginalArtist: 'false',
+		}
+		const text = writeChartFile(chart)
+		expect(text).toContain('MysteryString = "hello"')
+		expect(text).toContain('MysteryNumber = 42')
+		expect(text).toContain('MysteryDecimal = -1.5')
+		expect(text).toContain('MysteryBool = false')
+		expect(text).toContain('OriginalArtist = false')
+		expect(text).not.toContain('OriginalArtist = "false"')
+	})
+
 	it('preserves future / unknown keys the parser has never heard of', () => {
 		const chart = createEmptyChart({ format: 'chart' })
 		chart.metadata.extraChartSongFields = { FutureField: 'future-value', Boss: '1' }

src/chart/chart-writer.ts

@@ -84,20 +84,50 @@ function serializeSongSection(chart: ParsedChart): string[] {
 
 	// Round-trip any `[Song]` keys the parser didn't claim (deprecated
 	// Moonscraper / GHTCP fields — `Player2`, `HoPo`, `PreviewEnd`, `MediaType`,
-	// audio-stream filenames, etc.). Values are preserved verbatim: if the
-	// source didn't quote the value, we don't quote it here either. Consumers
-	// should treat these as opaque and never synthesize them — editors should
-	// discover audio via folder scan rather than trust `*Stream` values here.
+	// audio-stream filenames, etc.). The parser strips enclosing quotes on
+	// read, so values stored here are always bare; we re-quote per the .chart
+	// spec field-type table on write. Moonscraper rejects unquoted stream
+	// filenames (`MusicStream = song.ogg` fails to load audio), so getting the
+	// quoting right matters for game compatibility, not just round-tripping.
 	if (m.extraChartSongFields) {
 		for (const [key, value] of Object.entries(m.extraChartSongFields)) {
-			lines.push(`  ${key} = ${value}`)
+			lines.push(`  ${key} = ${formatExtraSongValue(key, value)}`)
 		}
 	}
 
 	lines.push('}')
 	return lines
 }
 
+// `[Song]` keys whose values must stay unquoted even though the value is a
+// non-primitive string. Per the .chart spec, `Player2` is the only `bare
+// string` field — every other string-typed field is quoted. Numeric and
+// boolean values are handled by `BARE_VALUE_RE` below, so they don't need an
+// entry here.
+const BARE_STRING_SONG_FIELDS = new Set<string>(['Player2'])
+
+// Primitive literals (`number`, `decimal`, `boolean`) that the spec emits
+// bare. The spec doesn't list any boolean-typed [Song] fields, but the corpus
+// shows `OriginalArtist = false` written bare in every chart that uses it, and
+// this leaves room for any future spec additions. Booleans are matched
+// case-sensitively per the spec — `True`/`TRUE` would be malformed values and
+// fall through to the quoting branch, which is defensible.
+const BARE_VALUE_RE = /^(?:-?\d+(?:\.\d+)?|true|false)$/
+
+/**
+ * Format a value for an `extraChartSongFields` key. The parser strips quotes
+ * on read, so values arrive bare; this re-applies them on write. The rule:
+ * primitive-literal values (numeric / boolean) stay bare, `Player2` stays
+ * bare per spec, and everything else gets quoted. Quoting strings by default
+ * matches the spec (every string / file-path field is quoted) and the
+ * 62K-chart corpus, and fixes the Moonscraper audio-load bug for unquoted
+ * stream filenames.
+ */
+function formatExtraSongValue(key: string, value: string): string {
+	if (BARE_STRING_SONG_FIELDS.has(key)) return value
+	return BARE_VALUE_RE.test(value) ? value : `"${value}"`
+}
+
 // ---------------------------------------------------------------------------
 // [SyncTrack] section
 // ---------------------------------------------------------------------------