tests/cases/conformance/classes/classDeclarations/classImplementsMergedClassInterface.ts(9,7): error TS2420: Class 'C2' incorrectly implements interface 'C1'. Property 'x' is missing in type 'C2'. tests/cases/conformance/classes/classDeclarations/classImplementsMergedClassInterface.ts(12,7): error TS2420: Class 'C3' incorrectly implements interface 'C1'. Property 'y' is missing in type 'C3'. tests/cases/conformance/classes/classDeclarations/classImplementsMergedClassInterface.ts(16,7): error TS2420: Class 'C4' incorrectly implements interface 'C1'. Property 'x' is missing in type 'C4'. ==== tests/cases/conformance/classes/classDeclarations/classImplementsMergedClassInterface.ts (3 errors) ==== declare class C1 { x : number; } interface C1 { y : number; } class C2 implements C1 { // error -- missing x ~~ !!! error TS2420: Class 'C2' incorrectly implements interface 'C1'. !!! error TS2420: Property 'x' is missing in type 'C2'. } class C3 implements C1 { // error -- missing y ~~ !!! error TS2420: Class 'C3' incorrectly implements interface 'C1'. !!! error TS2420: Property 'y' is missing in type 'C3'. x : number; } class C4 implements C1 { // error -- missing x ~~ !!! error TS2420: Class 'C4' incorrectly implements interface 'C1'. !!! error TS2420: Property 'x' is missing in type 'C4'. y : number; } class C5 implements C1 { // okay x : number; y : number; }