getInteropBlock() to work with null prototype objects

[jdalton]

…e objects

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:

Description

Currently, rollup attempts to detect how exports should be generated based on the exported values from the module entry.

1. If there is a default export, export the default property as-is.
2. If there is a named export (named), rollup returns an object with the named property.
3. If there are both a default export and a named export (named), rollup returns an object with the default and the named property. It's important to note that if no output.exports property is set, rollup warns in this case.

On the other hand, when importing the default value from an external module, rollup injects some interop code extract the code right default value. This interop checks the presence of the default property on the exported object using module.hasOwnProperty('default').

I recently ran into a case where the interop code throws an error because hasOwnProperty is not defined on the external module. This happens because the module (module/a) has a single default export and the default export value has no prototype. In this case, if another module (module/b) imports the default export the interop code will throw because hasOwnProperty is not defined on the object.

/* `module/a` original code */
export default { __proto__: null, name: 'a' };

/* `module/a` generated code */
define('module/a', function () { 'use strict';
  var main = { __proto__: null, name: 'a' };
  return main;
});

/* `module/b` original code */
import a from 'module/a';
console.log(a.name);

/* `module/b` generated code */
define('module/b', ['module/a'], function (a) { 'use strict';
  a = a && a.hasOwnProperty('default') ? a['default'] : a;
  //              ^ throws here because a does inherit from object!
  console.log(a.name);
});

[jdalton]

I need to follow-up with a test specifically for the null prototype case. Current PR has just existing tests modified.

Update: Added unit test to test this case specifically ✅

[codecov]

Codecov Report

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@@            Coverage Diff            @@
##             master    #3420   +/-   ##
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  Coverage          ?   93.29%           
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  Files             ?      172           
  Lines             ?     6114           
  Branches          ?     1823           
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  Hits              ?     5704           
  Misses            ?      218           
  Partials          ?      192

Impacted Files	Coverage Δ
src/finalisers/shared/getInteropBlock.ts	100% <ø> (ø)

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[lukastaegert]

Looks good to me, thanks!

[lukastaegert]

Update: Added unit test to test this case specifically ✅

Very welcome, and important to document why we do it this way, thanks a lot!

[jdalton]

Thank you @lukastaegert!