==== tests/cases/compiler/callSignatureAssignabilityInInheritance.ts (2 errors) ====
    module CallSignature {
        interface Base { // T
            // M's
            (x: number): void;
            (x: number, y: number): void;
        }
    
        // S's
        interface I extends Base {
            // N's
            (x: number): number; // ok because base returns void
            (x: number, y: number): boolean; // ok because base returns void
            <T>(x: T): string; // ok because base returns void
        }
    
        interface Base2 { // T
            // M's
            (x: number): number;
        }
    
        // S's
        interface I2 extends Base2 {
                  ~~
!!! callSignatureAssignabilityInInheritance.ts(22,15): error TS2143: Interface 'CallSignature.I2' cannot extend interface 'CallSignature.Base2':
!!! 	Call signatures of types 'I2' and 'Base2' are incompatible.
            // N's
            (x: number): string; // error because base returns non-void;
        }
    
        // S's
        interface I3 extends Base2 {
            // N's
            <T>(x: T): string; // ok, adds a new call signature
        }
    }
    
    module MemberWithCallSignature {
        interface Base { // T
            // M's
            a: (x: number) => void;
            a2: (x: number, y: number) => void;
            a3: <T>(x: T) => void;
        }
    
        // S's
        interface I extends Base {
            // N's
            a: (x: number) => number; // ok because base returns void
            a2: (x: number, y: number) => boolean; // ok because base returns void
            a3: <T>(x: T) => string; // ok because base returns void
        }
    
        interface Base2 { // T
            // M's
            a: (x: number) => number;
            a2: <T>(x: T) => T;
        }
    
        // S's
        interface I2 extends Base2 {
                  ~~
!!! callSignatureAssignabilityInInheritance.ts(57,15): error TS2143: Interface 'MemberWithCallSignature.I2' cannot extend interface 'MemberWithCallSignature.Base2':
!!! 	Types of property 'a' of types 'I2' and 'Base2' are incompatible:
!!! 		Call signatures of types '(x: number) => string' and '(x: number) => number' are incompatible.
            // N's
            a: (x: number) => string; // error because base returns non-void;
        }
    
        // S's
        interface I3 extends Base2 {
            // N's
            a2: <T>(x: T) => string; // error because base returns non-void;
        }
    }