==== tests/cases/conformance/types/primitives/string/assignFromStringInterface2.ts (2 errors) ====
    interface String {
        doStuff(): string;
    }
    
    interface NotString {
        doStuff(): string;
        toString(): string;
        charAt(pos: number): string;
        charCodeAt(index: number): number;
        concat(...strings: string[]): string;
        indexOf(searchString: string, position?: number): number;
        lastIndexOf(searchString: string, position?: number): number;
        localeCompare(that: string): number;
        match(regexp: string): string[];
        match(regexp: RegExp): string[];
        replace(searchValue: string, replaceValue: string): string;
        replace(searchValue: string, replaceValue: (substring: string, ...args: any[]) => string): string;
        replace(searchValue: RegExp, replaceValue: string): string;
        replace(searchValue: RegExp, replaceValue: (substring: string, ...args: any[]) => string): string;
        search(regexp: string): number;
        search(regexp: RegExp): number;
        slice(start?: number, end?: number): string;
        split(separator: string, limit?: number): string[];
        split(separator: RegExp, limit?: number): string[];
        substring(start: number, end?: number): string;
        toLowerCase(): string;
        toLocaleLowerCase(): string;
        toUpperCase(): string;
        toLocaleUpperCase(): string;
        trim(): string;
        length: number;
        substr(from: number, length?: number): string;
        [index: number]: string;
    }
    
    var x = '';
    var a: String;
    var b: NotString;
    
    a = x; 
    a = b; 
    
    b = a; 
    b = x; 
    
    x = a; // expected error
    ~
!!! Type 'String' is not assignable to type 'string'.
    x = b; // expected error
    ~
!!! Type 'NotString' is not assignable to type 'string'.