fix: stylus - handle relative sourcemap sources(#513)

Author: Gin-Quin

src/transformers/stylus.ts

@@ -4,8 +4,13 @@ import stylus from 'stylus';
 
 import { getIncludePaths } from '../modules/utils';
 
+import type { SourceMap } from 'magic-string';
 import type { Transformer, Options } from '../types';
 
+type StylusRendererWithSourceMap = ReturnType<typeof stylus> & {
+  sourcemap: SourceMap;
+};
+
 const transformer: Transformer<Options.Stylus> = ({
   content,
   filename,
@@ -20,15 +25,20 @@ const transformer: Transformer<Options.Stylus> = ({
     const style = stylus(content, {
       filename,
       ...options,
-    }).set('sourcemap', options.sourcemap);
+    }).set('sourcemap', options.sourcemap) as StylusRendererWithSourceMap;
 
     style.render((err, css) => {
       // istanbul ignore next
       if (err) reject(err);
+      if (style.sourcemap?.sources) {
+        style.sourcemap.sources = style.sourcemap.sources.map((source) =>
+          path.resolve(source),
+        );
+      }
 
       resolve({
         code: css,
-        map: (style as any).sourcemap,
+        map: style.sourcemap,
         // .map() necessary for windows compatibility
         dependencies: style
           .deps(filename as string)