Fix support for async functions as config

[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 #3470

Description

Don't know how this could slip past the radar. We had tests for configs as Promises and configs as functions, but functions that return promises...
Now async functions are supported again.

[rollup-bot]

Thank you for your contribution! ❤️

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

npm install rollup/rollup#gh-3470-async-function-config

or load it into the REPL:
https://rollupjs.org/repl/?circleci=10214

[codecov]

Codecov Report

Merging #3472 into master will not change coverage by %.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3472   +/-   ##
=======================================
  Coverage   95.81%   95.81%           
=======================================
  Files         174      174           
  Lines        5898     5898           
  Branches     1737     1736    -1     
=======================================
  Hits         5651     5651           
  Misses        127      127           
  Partials      120      120           

Impacted Files	Coverage Δ
cli/run/loadConfigFile.ts	95.55% <100.00%> (ø)

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[3cp]

I am seeing syntax error in my CI task running nodejs v8. This probably should be released as breaking change since it does not run on nodejs v8.

> bcx-validation@1.2.0 build /home/runner/work/bcx-validation/bcx-validation
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> env BABEL_ENV=development rollup -c
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/home/runner/work/bcx-validation/bcx-validation/node_modules/rollup/dist/shared/loadConfigFile.js:484
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        ? (await import(url.pathToFileURL(fileName).href)).default
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                 ^^^^^^
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SyntaxError: Unexpected token import

[lukastaegert]

Node 8 is no longer supported since v2.0.0

[3cp]

Oh, I missed that :-) Obviously it is only broken on latest v2, as I didn't have any issue on last few v2 versions.