[ButtonBase] Fix process is not defined

[eps1lon]

Closes #13247

I tried to not mock process but we execute on dependencies that are built for node (e.g. enzyme) so not polyfilling this will cause all sorts of problems in transitive dependencies.

A better place for removing the mock might be our visual regression tests.

[KevinGrandon]

I think this should work, thank you very much!

[oliviertassinari]

It would be great to have some sort of regression tests. The best story for this problem so far is that the only usage of process that is OK is process.env.NODE_ENV.

[KevinGrandon]

It would be great to have some sort of regression tests. The best story for this problem so far is that the only usage of process that is OK is process.env.NODE_ENV.

Actually I don't even think using that would be ok if you use MUI outside of webpack (unless you explicitly guard it with a typeof window === "undefined" && process type of check.

For the regression test, I assume we would need new infrastructure that does not use the existing webpack config. (Maybe just a html file with a link to the built bundle or something).

[eps1lon]

@KevinGrandon You have to convince the ecosystem first. Even react uses process.env.NODE_ENV in their build output.

Ideally we would run our regression tests with node: false but I can't get them to run locally (hangs) and the one build without polyfilled node returned a unhelpfull error message: https://circleci.com/gh/mui-org/material-ui/50343