Missing default when re-exporting with `export =`

[demurgos]

TypeScript Version:

nightly (1.9.0-dev.20160518-1.0)

Code

// export-default.ts
export let foo = "bar";
export default foo;

// re-export.ts
import alias = require("./export-default");
export = alias;

// main.ts
import foo from "./re-export";
console.log(foo);

Expected behavior:
This project should compile and executing main.ts should output "bar".

Actual behavior:
The following compilation error occurs:

main.ts(1,8): error TS1192: Module '"D:/projects/expor-default/re-export"' has no default export.

Comment
This issue prevents typings from exposing default exports ( original typings issue).

The syntax in re-export.ts is used as a workaround for TS preventing the augmentation of module-definitions re-exported with export * from "export-default" (see this issue and this comment).

[blakeembrey]

@mhegazy this is breaking a few people using default exports with Typings (see typings/typings#525).

[weswigham]

If I remember correctly, this is currently because we treat export = importedNamespace exactly as export * from "imported-module"; which, per spec, doesn't reexport default. This would be another point where the two syntaxes would diverge.

[blakeembrey]

Thanks @weswigham. In that case, I switched to the import = export = syntax because of a different TypeScript issue - originally I used export * here which is perfectly fine, except you can't augment things from export *. It seems like an odd limitation, since can't you realistically augment export * properties in JavaScript? (More information in typings/registry#270).

[mhegazy]

I highly recommend not mixing up export = patterns in this way. you should be using export default and export * from "mod" instead.
as @weswigham noted, this is currently working as intended. the module re-export.ts really does not have a default export.

[blakeembrey]

@mhegazy That means Typings can not work and will never work.

[blakeembrey]

If you look at the message above, that's how it used to work - but it broke people who wanted to augment modules.

[unional]

@mhegazy , IMO, I agree that the interop between ES2015/commonjs is hairy. Until a standard spec is derived we (the consumer) should avoid doing interop and use the module as it intended to be.

But currently it is a necessity as more and more people adapt to ES2015 thanks to Babel and TypeScript. I think we all appreciate the effort the team put in to make it a reality.

As for the interop, it has to be complete. As now commonjs -> ES2015 works (except #7398), and ES2015 -> commonjs also possible:

import alias = require("./export-default");
export = alias;

the solution has to be complete and cannot leave out the export default part.
Currently this is a blocking issue. Please reconsider.