Please upgrade source-map to 0.7.2 to get speed improvements

[andreicristianpetcu]

Expected Behavior

Babel should use the latest source-map which is v0.7.2. v0.7.2 got support for WebAssembly and it is 10 times faster than the old one. More info here:

https://github.com/mozilla/source-map/blob/master/CHANGELOG.md#072
http://fitzgeraldnick.com/2018/02/26/speed-without-wizardry.html
https://hacks.mozilla.org/2018/01/oxidizing-source-maps-with-rust-and-webassembly/

Current Behavior

Babel uses an old version of source-map

Context

I want source-map to be newer in debugger.html and I see it uses an old source map package since babel requires it.

[babel-bot]

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so it's possible this won't be addressed swiftly.

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[andreicristianpetcu]

Here is the downstream issue firefox-devtools/debugger#5598

[andreicristianpetcu]

I'm personally interested in getting the update for: babel-generator, babel-cli, babel-core and babel-register since this is needed by debugger.html

[danez]

These speed improvements look awesome, but they also come with a price and that is that version >=0.7 requires node 8 at least.
As sad as this is but right now we cannot update to this newer version. We still support node 4 for babel 7 and even if we decide to drop node 4 because it runs out of support soon, then we would still support node 6 for at least a year or more.

[nicolo-ribaudo]

Can we install version >= 0.7 as an optionalDependency and only use it in node 8?

[realityking]

Babel should probably first update to 0.6.1 as that contains some breaking API changes, otherwise usage of 0.7 is out of the question anyway.

[danez]

I seems also the api changed, so we would need to support different versions in our code

Breaking change: new SourceMapConsumer now returns a Promise object that resolves to the newly constructed SourceMapConsumer instance, rather than returning the new instance immediately.

(ups wrong button :) )

[loganfsmyth]

Oh interesting, if there's no way to create a sourcemap consumer synchronously, I'm not sure there's any way we can use this, since currently Babel exposes primarily synchronous transformation APIs.

We've starting to add infrastructure for Babel's APIs being async, but that will take time and will likely require either dropping or rearchitecting babel-register from scratch, for instance. The cases for consumer for us are:

For babel/core, when merging source-maps in babel/core we have to return the merged map synchronously

For babel/register, require() hooks are synchronous, so without reworking babel-register to compile up front, it seems impossible for us to make use of any APIs in core that are async

node-source-map-support requires remapping stack traces synchronously, so it seems like that would also be a no-go?

[coreyfarrell]

@loganfsmyth Would you accept a patch to upgrade to source-map@0.6.1 for now so babel will use the 'latest possible'? I tested locally with coverage enabled, most files where source-map is imported had very high coverage:

-----------------------------------------------------------------------|----------|----------|----------|----------|-------------------|
File                                                                   |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
-----------------------------------------------------------------------|----------|----------|----------|----------|-------------------|
 packages/babel-cli/src/babel/file.js                                  |        0 |        0 |        0 |        0 |                   |
 packages/babel-core/src/transformation/file/merge-map.js              |    97.85 |    90.24 |      100 |    98.85 |               302 |
 packages/babel-generator/src/source-map.js                            |      100 |    95.83 |      100 |      100 |                20 |
 packages/babel-helper-transform-fixture-test-runner/src/index.js      |    85.16 |       76 |    89.47 |    87.29 |... 72,275,284,310 |

I'm not sure how to get test coverage to that code in babel-cli. That source uses SourceMapGenerator and SourceMapConsumer. SourceMapConsumer is used with a single parameter so I believe it should be OK. Basing this idea off the git diff between source-map 0.5.7 and 0.6.0 (I couldn't find a changelog detailing breaking changes).

[jordanbtucker]

This will also fix an annoying issue in VS Code.

source-map@<0.7.1 has an invalid typings field in its package.json which is causing VS Code to report an error that it can't find the type declarations. This is fixed in source-map@>=0.7.1.

[jridgewell]

Closed with #14253