Compiler gives unhelpful error messages in the presence of multiple default exports

[MartyIX]

Proposed fix for #3886

The patch is not finished. I would just like to get some feedback from you guys if I'm on the right track or if you would choose another approach.

Thanks!

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[MartyIX]

Issue #95 seems very similar to this one. Maybe another IF statement would fixed it as well.

[DanielRosenwasser]

You need to add a diagnostic with a unique code to diagnosticMessages.json. Then use the appropriate generated code.

[DanielRosenwasser]

Make the message "A module cannot have multiple default exports."

[DanielRosenwasser]

Can you add the following 3 tests?

tests/cases/conformance/es6/modules/defaultExportWIthOverloads01.ts

export default function f();
export default function f(x: string);
export default function f(...args: any[]) {
}

tests/cases/conformance/es6/modules/multipleDefaultExports03.ts

export default function f() {
}
export default function f() {
}

tests/cases/conformance/es6/modules/multipleDefaultExports04.ts

export default class C {
}

export default class C {
}

[DanielRosenwasser]

Sorry, I didn't want two separate files, I wanted both declarations to occur in the same file.

Also, can you add multipleDefaultExports04?

export default function f() {
}
export default function f() {
}

[DanielRosenwasser]

Hey @MartyIX - unfortunately I gave some bad feedback a little bit earlier regarding multiple default-exported functions. I said that "Duplicate function implementation" was the correct error message to give; however, I think that would be the right message to give only if the function declaration names are not the same.

Still, I think this work is great and we can take it in now. Thanks for the fix!