tests/cases/compiler/genericArrayExtenstions.ts(1,22): error TS1148: Cannot compile external modules unless the '--module' flag is provided.
tests/cases/compiler/genericArrayExtenstions.ts(1,22): error TS2421: Class 'ObservableArray<T>' incorrectly implements interface 'T[]':
  Property 'length' is missing in type 'ObservableArray<T>'.


==== tests/cases/compiler/genericArrayExtenstions.ts (2 errors) ====
    export declare class ObservableArray<T> implements Array<T> { // MS.Entertainment.ObservableArray
                         ~~~~~~~~~~~~~~~
!!! error TS1148: Cannot compile external modules unless the '--module' flag is provided.
                         ~~~~~~~~~~~~~~~
!!! error TS2421: Class 'ObservableArray<T>' incorrectly implements interface 'T[]':
!!! error TS2421:   Property 'length' is missing in type 'ObservableArray<T>'.
    concat<U extends T[]>(...items: U[]): T[];
    concat(...items: T[]): T[];
    }
    