Commits on Feb 16, 2023

1. Handle "simple" (missing origin) source mappings in minifier output (f… …

   …acebook#928)
   
   Summary:
   Pull Request resolved: facebook#928
   
   Fixes facebook#927
   
   Terser, unlike the previous default minifier UglifyES, produces source maps whose entries may contain "simple mappings" - that is entries with a generated line+col but no original location.
   
   When Metro processes minified output ahead of serialization, it doesn't correctly handle these entries. Instead it incorrectly detects them as complete mappings and produces a merged source map with `-1` origin line numbers in place of simple mappings.
   
   Some tools will reject the whole source map (which is otherwise correct) based on the appearance of a negative line number.
   
   The issue comes down to the conversion of raw mappings to `BabelSourceMapSegments` in `toBabelSegments`, which currently generates entries for simple mappings with `null` `origin` *properties*, such as:
   
   ```
   {
     generated: {
       column: 2,
       line: 1
     },
     origin: {
       column: null,
       line: null
     },
     // ...
   }
   ```
   
   According to the Flow type for `BabelSourceMapSegments`, that's incorrect. `origin` itself is optional and should be missing - the properties of `origin` are not nullable.
   
   Based on the presence of the `origin` property in that object, `toSegmentTuple` generates a 4-tuple and we go on to add a "source mapping" rather than a "simple mapping".
   
   This fixes `toBabelSegments` to omit `origin` unless `line` and `column` are both populated. The final source map output is then correct.
   
   Changelog: [Fix] Source maps may have invalid entries when using Terser minification.
   
   Reviewed By: motiz88
   
   Differential Revision: D43351987
   
   fbshipit-source-id: 706cf2e90cb33ebc8223b449b2c280156512c9a4

   

   robhogan authored and facebook-github-bot committed Feb 16, 2023
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