d.ts with import statement exports types that are not marked exported

[evmar]

TypeScript Version: typescript@2.7.0-dev.20171027 (also 2.4 and 2.5)

Code

// extra.ts
export var x = 3;

// iface.d.ts
import {x} from './extra';
// note: this next line is *not* exported
declare interface Foo { bar: string; }

// user.ts
import {Foo} from './iface';

Expected behavior:
This should fail to compile, because iface.d.ts did not export the Foo type. Error message should be

 error TS2305: Module ... has no exported member 'Foo'.

Actual behavior:
It compiles.

Extra notes:

1. if iface.d.ts has no import statement, but instead uses export {} to become a module, then expected error is produced
2. if you remove import/export statements from iface.d.ts, then as expected you get the 'is not a module' error
3. if you rename iface.d.ts to iface.ts, then expected error is produced

In a .d.ts file we normally assume that the things you're writing are public exports, else you would not be writing them.

if iface.d.ts has no import statement, but instead uses export {} to become a module, then expected error is produced

This is interesting though, I didn't know export {} would make other things not exported. @RyanCavanaugh is that intentional?

[mhegazy]

Sometime between 0.8.3 and 0.9.1 we saw that ample declare export did not look that nice in .d.ts files. as a result declare was banned inside a declare block, and export was deemed "optional" in an ambient context (i.e. a declare declaration, or a .d.ts file).

ES6 modules come along, and we need to support them. export {} and export default have semantics that allow for exporting/renaming a local declaration. the current rules we had for .d.ts files did not fit with that. Just keeping the rule of implicit exporting means that we export declarations on the .d.ts that were not in the .ts. We added an exception for export {} and export default.

If the .d.ts file/ambient module contains at least one export {} or an export default, only exported declarations will be visible.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.