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commit: 8e7f8c3

The @babel/runtime/regenerator/index.js does have side effects because it registers regeneratorRuntime to the global object. As for other runtime helpers, if they do not write to global object, they should be considered pure.

c.f. #17463 (comment)

I didn't realize that that file is also in Babel 8. Is has a Todo comment mentioning to remove it, we should actually do it.

I didn't realize that that file is also in Babel 8. Is has a Todo comment mentioning to remove it, we should actually do it.

Yeah. If we want to keep that file in Babel 7, we can overwrite the package.json#files config (and the exports config) in Babel 8 so that at least this file will not be published in Babel 8. We can eventually remove this file when we discontinue Babel 7.

Conditional package.json#files doesn't seem to work. I changed it to a runtime error for now.

I plan to split the Babel 8 vs Babel 7 branch soon, then we can delete the file.