Class MappingsEncoder

src/utils/MappingsEncoder.ts:42–132

// Buffers completed lines of segments and VLQ-encodes them in batches, so producing
// an encoded map never holds more than ~SEGMENTS_PER_FLUSH decoded segments
export class MappingsEncoder {
  declare private out: string
  declare private pos: number
  declare private lines: FullSegment[][]
  declare private buffered: number
  declare private needsComma: boolean
  declare private prevGenColumn: number
  declare private prevSourceIndex: number
  declare private prevSourceLine: number
  declare private prevSourceColumn: number
  declare private prevNameIndex: number

  constructor() {
    this.out = ''
    this.pos = 0
    this.lines = []
    this.buffered = 0
    this.needsComma = false
    this.prevGenColumn = 0
    this.prevSourceIndex = 0
    this.prevSourceLine = 0
    this.prevSourceColumn = 0
    this.prevNameIndex = 0
  }

  endLine(segments: FullSegment[]): void {
    this.lines.push(segments)
    // count the line itself too, so content dominated by line breaks also drains
    this.buffered += segments.length + 1
    if (this.buffered >= SEGMENTS_PER_FLUSH)
      this.drain(null)
  }

  segments(segments: FullSegment[]): void {
    this.drain(segments)
  }

  finish(segments: FullSegment[]): string {
    this.drain(segments)
    this.flush()
    return this.out
  }

  private drain(trailing: FullSegment[] | null): void {
    const lines = this.lines
    const lineCount = lines.length

    for (let l = 0; l <= lineCount; l++) {
      const line = l < lineCount ? lines[l] : trailing
      if (line === null)
        break

      for (let i = 0; i < line.length; i++) {
        if (this.pos > FLUSH_THRESHOLD)
          this.flush()
        const segment = line[i]
        if (this.needsComma)
          scratch[this.pos++] = COMMA