addMapping(aArgs) {
    const generated = util.getArg(aArgs, 'generated')
    const original = util.getArg(aArgs, 'original', null)
    let source = util.getArg(aArgs, 'source', null)
    let name = util.getArg(aArgs, 'name', null)

    if (!this._skipValidation) {
      this._validateMapping(generated, original, source, name)
    }

    if (source != null) {
      source = String(source)
      if (!this._sources.has(source)) {
        this._sources.add(source)
      }
    }

    if (name != null) {
      name = String(name)
      if (!this._names.has(name)) {
        this._names.add(name)
      }
    }

    this._mappings.add({
      generatedLine: generated.line,
      generatedColumn: generated.column,
      originalLine: original != null && original.line,
      originalColumn: original != null && original.column,
      source,
      name,
    })
  }
Add a single mapping from original source line and column to the generated
source's line and column for this source map being created. The mapping
object should have the following properties:

  - generated: An object with the generated line and column positions.
  - original: An object with the original line and column positions.
  - source: The original source file (relative to the sourceRoot).
  - name: An optional original token name for this mapping.