Source Code Transformations

If a plugin transforms source code, it should generate a sourcemap automatically, unless there's a specific sourceMap: false option. Rolldown only cares about the mappings property (everything else is handled automatically). magic-string provides a simple way to generate such a map for elementary transformations like adding or removing code snippets.

If it doesn't make sense to generate a sourcemap, return an empty sourcemap:

return {
  code: transformedCode,
  map: { mappings: '' },
};

If the transformation does not move code, you can preserve existing sourcemaps by returning null:

return {
  code: transformedCode,
  map: null,
};