Interfaces with all members optional is almost the same as 'any'

[bman61]

TypeScript Version: 1.8.0 / nightly (2.0.0-dev.201xxxxx)

Code

interface AllMembersOptional {
    first?: string;
    second?: number;
}

let a: AllMembersOptional = 7;
let b: AllMembersOptional = () => 7;

Expected behavior:
compiler error '7' is not type AllMembersOptional -- let a: AllMembersOptional = 7;
compiler error 'function: number' is not type AllMembersOptional -- let b: AllMembersOptional = () => 7;

Actual behavior:
no compiler errors or warnings and the following javascript is generated:

var a = 7;
var b = function () { return 7; };

Actual example
Referencing angular.d.ts and converting an angular directive

angular.module('test').directive('custom', function () {
  return {
    controller: 'testCtrl',
    template: '<div></div>,
    //...
  };
});

carelessly into a component

angular.module('test').component('custom', function () {
  return {
    controller: 'testCtrl',
    template: '<div></div>,
    //...
  };
});

generates no typescript compiler error messages and will fail at run-time because the options parameter needs to be an object

angular.module('test').component('custom', {
    controller: 'testCtrl',
    template: '<div></div>,
    //...
  }
);

options parameter cannot a function (or number or string etc).
Just about anything passed in for a parameter of an interface type with all optional parameters will be allowed by typescript

[sandersn]

See this FAQ answer. An interface with all optional properties is similar to an empty interface in this case.

[bman61]

It is similar to an empty (i.e. useless) interface but is it the same?

Per FAQ:
In general, you should never find yourself declaring an interface with no properties.

If never is a good idea, would it make sense to have a compiler flag to issue warnings/errors?

[sandersn]

Take a look at #7485 and #3842 -- #7845 is an proposal to fix this based on code from the closed PR #3842.

[bman61]

Looked at both. #3842 definitely discusses the issue and issues with implementing. this helps a lot. thanks