[pluginutils] attachScopes leaks for-loop variables defined with const/let to outer scope

[eight04]

• Rollup Plugin Name: pluginutils
• Rollup Plugin Version: 4.0.0
• Rollup Version:
• Operating System (or Browser): Windows 10
• Node Version: 13.8.0
• Link to reproduction (⚠️ read below):
  • ForStatement: https://repl.it/repls/StaidAvariciousFactor
  • ForInStatement: https://repl.it/repls/ElatedWelllitCharacters

Expected Behavior

The outer scope shouldn't contain variable a thus it should print

false
true

Actual Behavior

true
true

Additional Information

It has been reported once but the issue is closed:
#113

[shellscape]

Thanks for opening an issue. Pull requests to resolve this issue are welcome. This is unlikely to get a fix without community contribution.

[stale]

Hey folks. This issue hasn't received any traction for 60 days, so we're going to close this for housekeeping. If this is still an ongoing issue, please do consider contributing a Pull Request to resolve it. Further discussion is always welcome even with the issue closed. If anything actionable is posted in the comments, we'll consider reopening it. ⓘ