Minimally working example for postcss-import where a file that only includes import lines is not represented in the sourcemap.
npm i
npm run postcss-ok
Open test.html in your browser.
The dev-tools will show a file named style-withcomment.css In the file, there is the dummy comment, and the import statements.
npm run postcss-nok
Open test.html in your browser.
The dev-tools will not show a file named style-withoutcomment.css