Do not report errors for classes and interfaces merging

src/compiler/checker.ts

@@ -12874,11 +12874,6 @@ namespace ts {
             }
             checkClassLikeDeclaration(node);
 
-            // Interfaces cannot be merged with non-ambient classes.
-            if (getSymbolOfNode(node).flags & SymbolFlags.Interface && !isInAmbientContext(node)) {
-                error(node, Diagnostics.Only_an_ambient_class_can_be_merged_with_an_interface);
-            }
-
             forEach(node.members, checkSourceElement);
         }
 
@@ -13164,16 +13159,6 @@ namespace ts {
                         checkIndexConstraints(type);
                     }
                 }
-
-                // Interfaces cannot merge with non-ambient classes.
-                if (symbol && symbol.declarations) {
-                    for (let declaration of symbol.declarations) {
-                        if (declaration.kind === SyntaxKind.ClassDeclaration && !isInAmbientContext(declaration)) {
-                            error(node, Diagnostics.Only_an_ambient_class_can_be_merged_with_an_interface);
-                            break;
-                        }
-                    }
-                }
             }
             forEach(getInterfaceBaseTypeNodes(node), heritageElement => {
                 if (!isSupportedExpressionWithTypeArguments(heritageElement)) {

src/compiler/diagnosticMessages.json

@@ -1620,10 +1620,6 @@
         "category": "Error",
         "code":2517
     },
-    "Only an ambient class can be merged with an interface.": {
-        "category": "Error",
-        "code": 2518
-    },
     "Duplicate identifier '{0}'. Compiler uses declaration '{1}' to support async functions.": {
         "category": "Error",
         "code": 2520

tests/baselines/reference/augmentedTypesClass2.errors.txt

@@ -1,24 +1,18 @@
-tests/cases/compiler/augmentedTypesClass2.ts(4,7): error TS2518: Only an ambient class can be merged with an interface.
-tests/cases/compiler/augmentedTypesClass2.ts(10,11): error TS2518: Only an ambient class can be merged with an interface.
 tests/cases/compiler/augmentedTypesClass2.ts(16,7): error TS2300: Duplicate identifier 'c33'.
 tests/cases/compiler/augmentedTypesClass2.ts(21,6): error TS2300: Duplicate identifier 'c33'.
 
 
-==== tests/cases/compiler/augmentedTypesClass2.ts (4 errors) ====
+==== tests/cases/compiler/augmentedTypesClass2.ts (2 errors) ====
     // Checking class with other things in type space not value space
 
     // class then interface
-    class c11 { // error
-          ~~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
+    class c11 {
         foo() {
             return 1;
         }
     }
 
-    interface c11 { // error
-              ~~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
+    interface c11 {
         bar(): void;
     }
 

tests/baselines/reference/augmentedTypesClass2.js

@@ -2,13 +2,13 @@
 // Checking class with other things in type space not value space
 
 // class then interface
-class c11 { // error
+class c11 {
     foo() {
         return 1;
     }
 }
 
-interface c11 { // error
+interface c11 {
     bar(): void;
 }
 

tests/baselines/reference/augmentedTypesInterface.errors.txt

@@ -1,10 +1,8 @@
-tests/cases/compiler/augmentedTypesInterface.ts(12,11): error TS2518: Only an ambient class can be merged with an interface.
-tests/cases/compiler/augmentedTypesInterface.ts(16,7): error TS2518: Only an ambient class can be merged with an interface.
 tests/cases/compiler/augmentedTypesInterface.ts(23,11): error TS2300: Duplicate identifier 'i3'.
 tests/cases/compiler/augmentedTypesInterface.ts(26,6): error TS2300: Duplicate identifier 'i3'.
 
 
-==== tests/cases/compiler/augmentedTypesInterface.ts (4 errors) ====
+==== tests/cases/compiler/augmentedTypesInterface.ts (2 errors) ====
     // interface then interface
 
     interface i {
@@ -16,15 +14,11 @@ tests/cases/compiler/augmentedTypesInterface.ts(26,6): error TS2300: Duplicate i
     }
 
     // interface then class
-    interface i2 { // error
-              ~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
+    interface i2 {
         foo(): void;
     }
 
-    class i2 {  // error
-          ~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
+    class i2 {
         bar() {
             return 1;
         }

tests/baselines/reference/augmentedTypesInterface.js

@@ -10,11 +10,11 @@ interface i {
 }
 
 // interface then class
-interface i2 { // error
+interface i2 {
     foo(): void;
 }
 
-class i2 {  // error
+class i2 {
     bar() {
         return 1;
     }

tests/baselines/reference/classAbstractMergedDeclaration.errors.txt

@@ -1,7 +1,3 @@
-tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(7,16): error TS2518: Only an ambient class can be merged with an interface.
-tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(8,11): error TS2518: Only an ambient class can be merged with an interface.
-tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(10,11): error TS2518: Only an ambient class can be merged with an interface.
-tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(11,16): error TS2518: Only an ambient class can be merged with an interface.
 tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(13,16): error TS2300: Duplicate identifier 'CC1'.
 tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(14,7): error TS2300: Duplicate identifier 'CC1'.
 tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(16,7): error TS2300: Duplicate identifier 'CC2'.
@@ -20,26 +16,18 @@ tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbst
 tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts(39,1): error TS2511: Cannot create an instance of the abstract class 'DCC1'.
 
 
-==== tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts (20 errors) ====
+==== tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMergedDeclaration.ts (16 errors) ====
     abstract class CM {}
     module CM {}
 
     module MC {}
     abstract class MC {}
 
     abstract class CI {}
-                   ~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
     interface CI {}
-              ~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
 
     interface IC {}
-              ~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
     abstract class IC {}
-                   ~~
-!!! error TS2518: Only an ambient class can be merged with an interface.
 
     abstract class CC1 {}
                    ~~~

tests/baselines/reference/classAndInterfaceWithSameName.errors.txt

@@ -1,37 +1,25 @@
-tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(1,7): error TS2518: Only an ambient class can be merged with an interface.
 tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(1,11): error TS2300: Duplicate identifier 'foo'.
-tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(2,11): error TS2518: Only an ambient class can be merged with an interface.
 tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(2,15): error TS2300: Duplicate identifier 'foo'.
-tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(5,11): error TS2518: Only an ambient class can be merged with an interface.
 tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(6,9): error TS2300: Duplicate identifier 'bar'.
-tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(9,15): error TS2518: Only an ambient class can be merged with an interface.
 tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts(10,9): error TS2300: Duplicate identifier 'bar'.
 
 
-==== tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts (8 errors) ====
+==== tests/cases/conformance/classes/classDeclarations/classAndInterfaceWithSameName.ts (4 errors) ====
     class C { foo: string; }
-          ~
-!!! error TS2518: Only an ambient class can be merged with an interface.
               ~~~
 !!! error TS2300: Duplicate identifier 'foo'.
-    interface C { foo: string; } // error
-              ~
-!!! error TS2518: Only an ambient class can be merged with an interface.
+    interface C { foo: string; }
                   ~~~
 !!! error TS2300: Duplicate identifier 'foo'.
 
     module M {
         class D {
-              ~
-!!! error TS2518: Only an ambient class can be merged with an interface.
             bar: string;
             ~~~
 !!! error TS2300: Duplicate identifier 'bar'.
         }
 
-        interface D { // error
-                  ~
-!!! error TS2518: Only an ambient class can be merged with an interface.
+        interface D {
             bar: string;
             ~~~
 !!! error TS2300: Duplicate identifier 'bar'.

tests/baselines/reference/classAndInterfaceWithSameName.js

@@ -1,13 +1,13 @@
 //// [classAndInterfaceWithSameName.ts]
 class C { foo: string; }
-interface C { foo: string; } // error
+interface C { foo: string; }
 
 module M {
     class D {
         bar: string;
     }
 
-    interface D { // error
+    interface D {
         bar: string;
     }
 }

tests/baselines/reference/clinterfaces.symbols

@@ -0,0 +1,52 @@
+=== tests/cases/compiler/clinterfaces.ts ===
+module M {
+>M : Symbol(M, Decl(clinterfaces.ts, 0, 0))
+
+    class C { }
+>C : Symbol(C, Decl(clinterfaces.ts, 0, 10), Decl(clinterfaces.ts, 1, 15))
+
+    interface C { }
+>C : Symbol(C, Decl(clinterfaces.ts, 0, 10), Decl(clinterfaces.ts, 1, 15))
+
+    interface D { }
+>D : Symbol(D, Decl(clinterfaces.ts, 2, 19), Decl(clinterfaces.ts, 3, 19))
+
+    class D { }
+>D : Symbol(D, Decl(clinterfaces.ts, 2, 19), Decl(clinterfaces.ts, 3, 19))
+}
+
+interface Foo<T> {
+>Foo : Symbol(Foo, Decl(clinterfaces.ts, 5, 1), Decl(clinterfaces.ts, 9, 1))
+>T : Symbol(T, Decl(clinterfaces.ts, 7, 14), Decl(clinterfaces.ts, 11, 10))
+
+    a: string;
+>a : Symbol(a, Decl(clinterfaces.ts, 7, 18))
+}
+
+class Foo<T>{
+>Foo : Symbol(Foo, Decl(clinterfaces.ts, 5, 1), Decl(clinterfaces.ts, 9, 1))
+>T : Symbol(T, Decl(clinterfaces.ts, 7, 14), Decl(clinterfaces.ts, 11, 10))
+
+    b: number;
+>b : Symbol(b, Decl(clinterfaces.ts, 11, 13))
+}
+
+class Bar<T>{
+>Bar : Symbol(Bar, Decl(clinterfaces.ts, 13, 1), Decl(clinterfaces.ts, 17, 1))
+>T : Symbol(T, Decl(clinterfaces.ts, 15, 10), Decl(clinterfaces.ts, 19, 14))
+
+    b: number;
+>b : Symbol(b, Decl(clinterfaces.ts, 15, 13))
+}
+
+interface Bar<T> {
+>Bar : Symbol(Bar, Decl(clinterfaces.ts, 13, 1), Decl(clinterfaces.ts, 17, 1))
+>T : Symbol(T, Decl(clinterfaces.ts, 15, 10), Decl(clinterfaces.ts, 19, 14))
+
+    a: string;
+>a : Symbol(a, Decl(clinterfaces.ts, 19, 18))
+}
+
+export = Foo;
+>Foo : Symbol(Foo, Decl(clinterfaces.ts, 5, 1), Decl(clinterfaces.ts, 9, 1))
+

tests/baselines/reference/clinterfaces.types

@@ -0,0 +1,52 @@
+=== tests/cases/compiler/clinterfaces.ts ===
+module M {
+>M : typeof M
+
+    class C { }
+>C : C
+
+    interface C { }
+>C : C
+
+    interface D { }
+>D : D
+
+    class D { }
+>D : D
+}
+
+interface Foo<T> {
+>Foo : Foo<T>
+>T : T
+
+    a: string;
+>a : string
+}
+
+class Foo<T>{
+>Foo : Foo<T>
+>T : T
+
+    b: number;
+>b : number
+}
+
+class Bar<T>{
+>Bar : Bar<T>
+>T : T
+
+    b: number;
+>b : number
+}
+
+interface Bar<T> {
+>Bar : Bar<T>
+>T : T
+
+    a: string;
+>a : string
+}
+
+export = Foo;
+>Foo : Foo<T>
+