Track updates of globals that are exported as default

[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 #3534

Description

When a global variable is assigned to a default export, Rollup does not track updates of the global variable even though it should, creating an unintended live-binding to the global variable where you would actually want a snapshot:
https://rollupjs.org/repl/?version=2.9.0&shareable=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

or even creating invalid code for ESM as you cannot directly reexport a global variable binding from a module. This is fixed by treating all global variables as having been (potentially) reassigned, which is true semantically.

Even though this is not the original issue of #3534, that issue will be solved here as well.

[rollup-bot]

Thank you for your contribution! ❤️

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

npm install rollup/rollup#gh-3534-updated-default-exported-global

or load it into the REPL:
https://rollupjs.org/repl/?circleci=10973

[codecov]

Codecov Report

Merging #3550 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3550      +/-   ##
==========================================
- Coverage   96.29%   96.29%   -0.01%     
==========================================
  Files         176      176              
  Lines        6044     6043       -1     
  Branches     1783     1781       -2     
==========================================
- Hits         5820     5819       -1     
  Misses        112      112              
  Partials      112      112              

Impacted Files	Coverage Δ
src/Module.ts	98.90% <100.00%> (-0.01%)	⬇️
src/ast/variables/GlobalVariable.ts	100.00% <100.00%> (ø)

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[guybedford]

Note that in ES modules, global = value is not a supported global assignment (strict mode!).

Also export default global should very much be supported as a snapshot at the time of execution and not a live binding.

[guybedford]

Also see previous bug - #2000.

[lukastaegert]

Note that in ES modules, global = value is not a supported global assignment (strict mode!)

Ah I see, but I think I can rework the test case so that we update the global variable in a legal way.

[guybedford]

Resolves #2000

[lukastaegert]

Unfortunately #2000 was not really resolved, at least the examples are still not working: https://rollupjs.org/repl/?circleci=10966&shareable=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

[guybedford]

I see, yes I misread that - I did think I had posted an issue for this snapshotting exactly, but apparently not.