Update source-map -> 0.8.0-beta.0 for compatibility with global fetch

[robhogan]

source-map@0.7.3 has an issue with buggy identification of node vs browser environment (it uses typeof fetch === 'function' to spot browsers) - See mozilla/source-map#349, mozilla/source-map#432 and fixes mozilla/source-map#350, mozilla/source-map#363.

This is an issue for React (Native) environments where fetch is often polyfilled, eg for testing or SSR. It's one of the last issues holding us back from making terser the default minifier for https://github.com/facebook/metro.

Importantly, this is also probably going to be an issue for all NodeJS users soon, as NodeJS moves forward with a native global fetch: nodejs/node#41749

Unfortunately, the only source-map release since that bug was fixed is 0.8.0-beta.0, dated Nov 2018.

• Comparison: mozilla/source-map@0.7.3...0.8.0-beta.0 .
• Changelog: https://github.com/mozilla/source-map/blob/master/CHANGELOG.md#080-beta0
  I've suggested they publish a release but I'm not optimistic (Release 0.8, or 0.7.4? mozilla/source-map#452).

Would you consider a dependency on a "prerelease", or is this a non-starter?

[jridgewell]

This is due to SourceMapConsumer using WASM, which uses fetch or fs.readFile to get the WASM bytes to instantiate. We could instead switch to @jridgewell/trace-mapping which provides a near drop-in API (and is faster, less memory intensive, and doesn't depend on WASM).

[fabiosantoscode]

🤔 this sounds tempting! The memory usage of source-map is definitely a problem. Though Terser also needs to handle the production of source maps. This library could help https://www.npmjs.com/package/vlq#-buffer

[robhogan]

It is only the SourceMapConsumer part of source-map that's problematic though - while it'd be great to replace the source-map dependency entirely, just using something else for consumption would address the particular issue that motivated this PR.

(Specifically: source-map@0.7.3 will still incorrectly detect the environment on require('../lib/read-wasm'), but the issue doesn't manifest until readWasm() is called (and throws), which is only on instantiation of SourceMapConsumer here)

[jridgewell]

I tried creating a PR for @jridgewell/trace-mapping, but I see that there's a test for sections sourcemaps, which it doesn't currently support (I don't know of any build tool that produces it). I can try adding it later this week, but we can merge this PR for now.

[robhogan]

@jridgewell - did you get anywhere with adding sections support? Otherwise, could we go with this PR as a mitigation?

Would love to move towards terser by default for React Native 👍

[jridgewell]

I did not yet. I'm happy with using 0.8.0-beta for now, and I'll try updating to my package at a later time. /cc @fabiosantoscode

Implemented as AnyMap in v0.3.8. See #1181 for PR to switch.

[fabiosantoscode]

Sounds good to me!

[fabiosantoscode]

Thanks for coming up with this @robhogan !

[marjorg]

This also closes #1030, who also deserves some credit for suggesting the fix ages ago :)