export { default } from "external-x" fails in non-ESM formats

[aapoalas]

• Rollup Version: 1.15.1
• Operating System (or Browser): Ubuntu 14.04
• Node Version: 8.10.0

How Do We Reproduce?

Link to Repl

Simple explanation: Re-exporting the default of an external module doesn't work.

Expected Behavior

If 'interop' is on, then the interop function should unwrap the default value and that value should then be returned (AMD module) / assigned to exports (CJS module) / ...

If 'interop' is off, then no unwrap should be done and the value from the module should be returned / assigned to exports as-is.

Actual Behavior

The 'interop' function unwraps the default value. Then value.default is returned / assigned to exports.

While I'm here

My use-case for Rollup has recently been with compiling ESM files into single AMD modules for use. The usage of these AMD modules does not care at all about original ESM format of the data and as such a simple return statement is enough. Occasionally, still, Rollup has been adding "exports" into the dependencies and using that as the means of output. It would be nice if there was a way to forbid this. But that's not really in any way connected with this bug report. Sorry about that.

[lukastaegert]

I’m working on a fix for this but due to other issues it may take another week to complete.

[lukastaegert]

Fix at #3084

[aapoalas]

Cool, thank you!