map.sourcesContent doesn't work together with map.from

const postcss = require('postcss');
const autoprefixer = require('autoprefixer');

const options = {
  from: 'src/test.css',
  to: 'src/test.css!postcss',
  map: {
    inline: false,
    annotation: false,
    sourcesContent: true,
    from: 'src/test.css'
  }
};

const instance = postcss([ autoprefixer({ browsers: '>0%' }) ]);

const result = instance.process('.test { border-radius: 5px }', options);

console.log(result.map.toJSON());

code below will produce sourcesContent: [ null ] instead of sourcesContent: [ '...' ] but will produce correct source name src/test.css.

If i will remove from option then sourcesContent will have correct value but sources will have test.css instead of src/test.css.

So there is no way to keep correct source name together with source content.

Looks like a two defects:

• options.from with full path truncated to basename by default and source map looses original source file path
• workaround with options.map.from keeps correct source file path but doesn’t work well with options.map. sourcesContent = true (breaks source content)

[yuriyostapenko]

Hi, I think I hit the same issue when running postcss on node-sass output. if map.from is set, the resulting .map file only references the empty virtual file, while all original sass maps are gone.

[ai]

I found problem. It was because of wrong content of opts.map.from. It should be relative from to (in this case it should be test.css).

I fixed docs: https://github.com/postcss/postcss/commit/30ac96f1a93484a591ba94a98e6a8aba519b3d37

opts.map.from is low-level option for rare edge cases. You should not use it.