`@layer` rules that do not have a block and do not have a trailing semi-colon break sourcemaps

@layer extensions {
  @layer one, two
}

This is equivalent to:

@layer extensions.one, extensions.two;

It parses correctly but fails to write a sourcemap :

Invalid mapping: {"generated":{"line":3,"column":-1},"source":"a.css","original":{"line":2,"column":16},"name":null}

The error goes away when I add a trailing semi-colon :

@layer extensions {
  @layer one, two;
}

I don’t have any knowledge about sourcemap internals and failed to pinpoint where it is going wrong.

I did add some tests to reproduce this : https://github.com/postcss/postcss/pull/1801

I don’t think the parsing the test is needed but I wanted to see how it was parsed. Maybe I am overlooking something there.

[ai]

The fix was released at 8.4.20.

[ai]

Thanks for the issue with a lot of details.

I will fix it. But very likely that I will do it after my vacation week later.