feat: migrate from source-map to @jridgewell/trace-mapping

[SimenB]

Summary

Same motivation as istanbuljs/v8-to-istanbul#185.

@jridgewell hi again! 😀 If this PR lands, there's only a single (non-transitive) usage of source-map in this repo, and that's https://github.com/facebook/jest/blob/5183c15a8e14089351d6403f4fdb72a6705aa379/e2e/coverage-handlebars/transform-handlebars.js. Would that use case be something you support as well?

Test plan

Green CI

[SimenB]

https://github.com/istanbuljs/v8-to-istanbul/blob/1f357fa2e994385b56ba505ca199eda46b233a89/index.d.ts#L14
https://github.com/mozilla/source-map/blob/58819f09018d56ef84dc41ba9c93f554e0645169/source-map.d.ts#L17
vs
https://github.com/jridgewell/trace-mapping/blob/d4ead19a18c805bd3af657f71ea72c48809f61db/src/types.ts#L7

[SimenB]

https://github.com/DefinitelyTyped/DefinitelyTyped/blob/94d284025fbc1c0f55f75c55f9ec7758260d672f/types/babel__core/index.d.ts#L30
vs
https://github.com/jridgewell/trace-mapping/blob/d4ead19a18c805bd3af657f71ea72c48809f61db/src/types.ts#L9

[jridgewell]

Would that use case be something you support as well?

trace-mapping is specific to consumer side of the sourcemap API. I've been thinking about making a package for the generator side (there are a ton of optimizations that could be made over SourceMapGenerator), but haven't done that yet.

However, you don't really need a generator for this simple usecase. You can just take advantage of a SectionedSourceMap:

import { AllMap, encodedMappings } from '@jridgewell/trace-map';

const output = [
  'const Handlebars = require("handlebars/dist/cjs/handlebars.runtime.js");\n',
  'module.exports = Handlebars.template(',
  code,
  ');\n',
];

const map = new AllMap({
  version: 3,
  sections: [
    {
      offset: {
        // 0-index, so count of newlines before `code`
        line: 1,
        // column offset of the injected code on its first line
        column: output[1].length,
      },
      map: pc.map,
    },
  ],
});

// map is now a regular, non-sectioned sourcemap that can be used everywhere.

// You need to manually JSONify the map from here, but I could add an export to do that for you.
const json = JSON.stringify({
  version: 3,
  file: map.file,
  names: map.names,
  sources: map.sources,
  sourcesContent: map.sourcesContent,
  // Depending on where this is going, you could use decodedMappings to avoid an encode->decode round trip.
  mappings: encodedMappings(map),
});

[SimenB]

Thanks @jridgewell! keeping the current code in this case seems fine, it's just an integration test. Happy to switch over if/when you release a generator package, though! 🙂

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