2.17 breaks bundle using @rollup/plugin-commonjs

[dstaley]

• Rollup Version: v2.17.0
• Operating System (or Browser): N/A
• Node Version (if applicable): v12.16.3
• Link to reproduction (IMPORTANT, read below): https://repl.it/repls/GlaringCheeryGlitch

Expected Behavior

The generated bundle either includes commonjsHelpers or does not reference it.

Actual Behavior

The generated bundle references a non-existing variable named commonjsHelpers. You can see the output on line 428 of output.js in the REPL. It's also produced below:

var freeGlobal =
  typeof commonjsGlobal == "object" &&
  commonjsGlobal &&
  commonjsHelpers.commonjsGlobal.Object === Object &&
  commonjsGlobal;

In v2.16.1, the same line is as follows:

var freeGlobal =
  typeof commonjsGlobal == "object" &&
  commonjsGlobal &&
  commonjsGlobal.Object === Object &&
  commonjsGlobal;

commonjsHelpers is only referenced once in the bundle, so I'm fairly sure it's not being included. Since this works with the latest version of @rollup/plugin-commonjs on v2.16.1 but not on v2.17.0, I'm unsure of whether this is an issue that needs to be solved in rollup or in the plugin, so please feel free to move this issue if everything is working as intended in rollup.

Also, just as a note, this prevents the entire bundle from working correctly, so it's preventing us from updating to v2.17.

For reference, this is the line from lodash that's being messed up.

[lukastaegert]

I'm looking into this, here is a minimal reproduction without the CJS plugin or lodash:
https://rollupjs.org/repl/?version=2.17.0&shareable=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

Note that it should actually look like this:
https://rollupjs.org/repl/?version=2.16.1&shareable=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

Fix should be upcoming.

[lukastaegert]

Fix at #3643, sorry for the regression.