Feature idea: strict modules

[rurban]

https://instagram-engineering.com/python-at-scale-strict-modules-c0bb9245c834 argues that certain properties violate strict modules.
The problems:

• slow startup and reload
• unsafe import side effects
• mutable global state

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The compiler already detects such misuse, using wrong times when code is executed. i.e. INIT vs BEGIN, or global code.

• no side-effects when loading a module, "no code on load":
  like io, changing global state - excluding adding functions. compared to doing that in the importer.
  i.e. no global print, no assignments, no if. just declarations and setting $VERSION, @ISA, ...
• Immutability and slots: classes and fields should be immutable by default with cperl. (the never implemented use oo :closed perl6 pragma)

The biggest violator would be Moose, that's why it became uncompilable in recent years with its new maintainer. Because global code inside modules was executed on load, and not on import.
A new strict mode for modules would detect that.