import namespace uses invalid variable (*) name when the only output is system

[sastan]

• Rollup Version: 2.26.0
• Operating System (or Browser): node
• Link to reproduction (IMPORTANT, read below):
  I tried to create a MR on sastan/rollup but failed. Here is the commit with the test case.

Expected Behavior

import * as dependency from 'dependency';
console.log(dependency);

Should generate systemjs bundle like:

System.register(['dependency'], function () {
	'use strict';
	var dependency$1;
	return {
		setters: [function (module) {
			dependency$1 = module;
		}],
		execute: function () {

			console.log(dependency$1);

		}
	};
});

Actual Behavior

The variable is named * which is not a valid variable name.

System.register(['dependency'], function () {
	'use strict';
	var *;
	return {
		setters: [function (module) {
			* = module;
		}],
		execute: function () {

			console.log(*);

		}
	};
});

This only happens when no other output is generated for that bundle. If a esm or cjs bundle is generated before the system bundle, the system is valid.

I am willing to create a working MR but i need some pointers where to start. For the moment i'm out of ideas.

[sastan]

Thank you.