Don't generate a default export for ES modules that don't have one

[marijnh]

I think this might fix #224

[marijnh]

Oh, failing tests. Trying to run them locally, both current master and with my patch, I get an error like

/home/marijn/tmp/rollup-plugin-commonjs/test/test.js:50
async function executeBundle ( bundle, { context, exports } = {} ) {
      ^^^^^^^^
SyntaxError: Unexpected token function

Which seems like an acorn configuration issue? Will try to guess what's going wrong and rely on CI to test.

[marijnh]

Fixed one of the tests, but the remaining failure is more involved -- it breaks because hasDefaultExport is (incorrectly) false for the sample module.exports = { default: 'foobar', __esModule: true }. Should we try to make it smarter, or is it, since this can never be determined with full accuracy, better to try and find an approach that doesn't break when the detection goes wrong?

[marijnh]

Oh, I finally got why I couldn't run the tests -- you're directly using async/await and I was using a pre-7.4 node. That only took me an hour to notice. I should go to bed.

[marijnh]

Hm, this solution is not really coherent—it's mixing up two interpretations of what default export means (CJS module.exports vs ES export default), and it only fixed my use case by incident. Closing this PR, let's continue in #224