Correctly include functions with side effects from side-effect-free modules

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:
Resolves #3942

Description

There was an issue with the inclusion logic for variables in modules without side effects that is fixed here.

[rollup-bot]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#gh-3942-side-effect-function-import

or load it into the REPL:
https://rollupjs.org/repl/?circleci=14121

[codecov]

Codecov Report

Merging #3944 (0246d1f) into master (bc2bf95) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3944   +/-   ##
=======================================
  Coverage   97.18%   97.18%           
=======================================
  Files         188      188           
  Lines        6684     6685    +1     
  Branches     1946     1947    +1     
=======================================
+ Hits         6496     6497    +1     
  Misses         99       99           
  Partials       89       89           

Impacted Files	Coverage Δ
src/ast/nodes/shared/Node.ts	100.00% <ø> (ø)
src/Module.ts	100.00% <100.00%> (ø)

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