Expose current filename to visitors

[Knagis]

#1170 added the ability for visitors to add dependencies, however, for the visitors to be able to do anything with such dependencies, it would be very useful if the current filename would be exposed as well.

This would allow a visitor to process a relative path specified in the CSS content.

I am currently trying to implement something like @value (https://github.com/css-modules/css-modules/blob/master/docs/values-variables.md) with visitor, but lack of the filename means i can't really implement @value name from "./foo.css" syntax.

Proposal: add sources property, same value as passed to StyleSheet() visitor (which i could use but don't want to as it needlessly serializes the whole AST..)

export interface VisitorOptions {
  readonly sources: readonly string[];
  addDependency: (dep: VisitorDependency) => void;
}

[devongovett]

This could work for transform but probably not for bundle since in that case there could be multiple stylesheets merged into one visitor pass and you won't know which one applies to which rules.

Can you use the Rule visitor to get the loc for that specific rule? Why does it need to be at the root level?

[Knagis]

@devongovett

loc doesn't expose the file name:

export interface Location2 {
  /**
   * The column number within a line, starting at 1 for first the character of the line. Column numbers are counted in UTF-16 code units.
   */
  column: number;
  /**
   * The line number, starting at 0.
   */
  line: number;
  /**
   * The index of the source file within the source map.
   */
  source_index: number;
}

wouldn't source_index be pointing to the correct file in the sources array?