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Error creating a SourceMapGenerator from a SourceMapConsumer of an index map (part 2)

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
35/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
javascript
Domain
tooling

Research direction

Start in lib/source-map-consumer.js around the sourceContentFor implementation and trace how lib/source-map-generator.js calls it from fromSourceMap. Run the provided index-map reproducer and confirm that an empty sourcesContent entry is preserved rather than treated as missing, without changing the behavior for null or undefined content.

Written by the indexing model from the issue text.

Description

needs-triage
;(async () => {
  let mozilla = require('source-map')
  let map;

  map = {
    version: 3,
    sections: [
      {
        offset: { line: 0, column: 0 },
        map: {
          version: 3,
          sources: ['123', '456'],
          sourcesContent: ['a\nb\nc\n', ''],
          mappings: 'AAAA;AACA;AACA;'
        }
      }
    ]
  }

  // this map works for some reason
  /*map = {
    version: 3,
    sources: ['123', '456'],
    sourcesContent: ['a\nb\nc\n', ''],
    mappings: 'AAAA;AACA;AACA;'
  }*/

  let consumer = await new mozilla.SourceMapConsumer(map)
  consumer.sourceRoot = null; // https://github.com/mozilla/source-map/issues/345
  let generator = mozilla.SourceMapGenerator.fromSourceMap(consumer)
  console.log(generator.toJSON())

})().catch(console.log)

This errors out:

Error: "456" is not in the SourceMap.
    at IndexedSourceMapConsumer.sourceContentFor (/tmp/node_modules/source-map/lib/source-map-consumer.js:840:11)
    at /tmp/node_modules/source-map/lib/source-map-generator.js:82:42
    at Array.forEach (<anonymous>)
    at Function.fromSourceMap (/tmp/node_modules/source-map/lib/source-map-generator.js:72:32)
    at /tmp/123/test.js:29:46

The issue is in here somewhere:

https://github.com/mozilla/source-map/blob/7a263408de1b60e60b6220ca3e36d9b3e4aa047d/lib/source-map-consumer.js#L880

Content is empty - '' - but it is still in the sourcemap. I believe it should be if (content == null) { check, i.e. null or undefined, letting empty string pass along.

this may be related to https://github.com/mozilla/source-map/issues/345, so tagging it just in case

Dominant language
JavaScript
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