Superfluous EmptyStatement created when parsing parenthized class or function expression in default export

[zjmiller]

Acorn parses the semicolon in both export default (class{}); and export default (function(){}); as an EmptyStatement. Esprima doesn't. The same issue arises with named classes and functions, as in export default (class A{}); and export default (function a(){});. The ES6 spec seems to support Esprima's interpretation of these cases.

This appears to stem from a difference in how Acorn and Esprima treat anonymous classes and functions in default exports. Acorn treats them as expressions and Esprima treats them as declarations. See estree/estree#98 for a recent discussion of this.

So Acorn treats export default class{} as involving a class expression. Because a semicolon is not needed here, Acorn says that in default exports, any semicolon following a class expression is unnecessary (and therefore ends up getting parsed as an EmptyStatement). This works great in export default class{}, but overgeneralizes when dealing with export default (class{}); and export default (class A{});. This is what's happening with functions as well.

[marijnh]

Indeed. Attached patch should help.