=== tests/cases/compiler/genericImplements.ts ===
class A { a; };
>A : Symbol(A, Decl(genericImplements.ts, 0, 0))
>a : Symbol(a, Decl(genericImplements.ts, 0, 9))

class B { b; };
>B : Symbol(B, Decl(genericImplements.ts, 0, 15))
>b : Symbol(b, Decl(genericImplements.ts, 1, 9))

interface I {
>I : Symbol(I, Decl(genericImplements.ts, 1, 15))

    f<T extends A>(): T;
>f : Symbol(f, Decl(genericImplements.ts, 2, 13))
>T : Symbol(T, Decl(genericImplements.ts, 3, 6))
>A : Symbol(A, Decl(genericImplements.ts, 0, 0))
>T : Symbol(T, Decl(genericImplements.ts, 3, 6))

} // { f: () => { a; } }

// OK
class X implements I {  
>X : Symbol(X, Decl(genericImplements.ts, 4, 1))
>I : Symbol(I, Decl(genericImplements.ts, 1, 15))

    f<T extends B>(): T { return undefined; }
>f : Symbol(f, Decl(genericImplements.ts, 7, 22))
>T : Symbol(T, Decl(genericImplements.ts, 8, 6))
>B : Symbol(B, Decl(genericImplements.ts, 0, 15))
>T : Symbol(T, Decl(genericImplements.ts, 8, 6))
>undefined : Symbol(undefined)

} // { f: () => { b; } }

// OK
class Y implements I {
>Y : Symbol(Y, Decl(genericImplements.ts, 9, 1))
>I : Symbol(I, Decl(genericImplements.ts, 1, 15))

    f<T extends A>(): T { return undefined; }
>f : Symbol(f, Decl(genericImplements.ts, 12, 22))
>T : Symbol(T, Decl(genericImplements.ts, 13, 6))
>A : Symbol(A, Decl(genericImplements.ts, 0, 0))
>T : Symbol(T, Decl(genericImplements.ts, 13, 6))
>undefined : Symbol(undefined)

} // { f: () => { a; } }

// OK
class Z implements I {
>Z : Symbol(Z, Decl(genericImplements.ts, 14, 1))
>I : Symbol(I, Decl(genericImplements.ts, 1, 15))

    f<T>(): T { return undefined; }
>f : Symbol(f, Decl(genericImplements.ts, 17, 22))
>T : Symbol(T, Decl(genericImplements.ts, 18, 6))
>T : Symbol(T, Decl(genericImplements.ts, 18, 6))
>undefined : Symbol(undefined)

} // { f: <T>() => T }