Stylus + Webpack: Source Map Integrity Through Autoprefixer for Deeply Nested Rules

Integration Boundary: Stylus → Webpack → Autoprefixer

Goal: compile a Stylus file that contains deeply nested selectors, generate a source map, pipe the CSS through autoprefixer, and verify that the final source map still points back to the original Stylus source.

Constraints: Using Stylus 0.63 with --source-map, the stylus-loader plugin in a Webpack 5 pipeline, and autoprefixer 10.x. The unresolved behavior is whether nested rule depth limits in Stylus (e.g., >10 levels) cause source map entries to be omitted after autoprefixer processes the CSS.

Questions:

• Does autoprefixer preserve source map entries for CSS rules that originate from deeply nested Stylus constructs?
• If mappings are lost, is there a configuration knob in stylus-loader or autoprefixer to increase depth or force full mapping?
• How does the interplay between stylus-loader’s sourceMap option and autoprefixer’s own source map handling affect the final mapping accuracy?