Fix a situation where two different imports with the same name are rendered

[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:
Hopefully resolves #2726

Description

This is basically a generalization of #2719. When two different default exports reference the same variable, it is possible that both are rendered as separate imports.

This is just again a fix for the import situation; the exports will still be rendered several times. The problem is that it is only known after tree-shaking if a default export can be identified with the original variable, at which point many other things have already been initialized using the separate variables.

A proper fix for the future might include

• calculating module dependencies AFTER tree-shaking
• before doing that
  • replacing default exports in the same module with exports of their original variables
  • removing default exports referencing variables from different modules
  • replacing imports with imports of the original variables (possibly from different modules)