Do we need to use "declare" for type aliased in d.ts files?

[mpawelski]

I read that declare is required for all top level non-interface elements (i.e. module, class, var) in a declaration .d.ts file.

But do we need it for type aliases too?

Right now this code in tests.d.ts file gives error:

interface ITest {
    foo: string;
    bar: string;
}


type IMyAlias = ITest;

A 'declare' modifier is required for a top level declaration in a .d.ts file.

For me type aliases are similar to interfaces in this case and should not require declare keyword.

[RyanCavanaugh]

declare should be optional on type aliases and interfaces.

declare type and declare interface are identical to type and interface

[DanielRosenwasser]

How does this affect #2994?

[yuit]

My understanding is that declare type is allowed as well as declare interface. So we need to stop giving an error for this case declare interface

[RyanCavanaugh]

Yui's interpretation is correct.

Since we already shipped type aliases this way, people have had to write declare type a bunch of times. We could break them and say "Write type, not declare type", but that would be a massive break for no real reason.

Having made that decision, it's only logical to allow declare interface as a synonym for interface for consistency's sake. There are still some places where we're slightly inconsistent, but type and interface at least should be fully aligned.