Fix duplicate identifier reporting in classes

src/compiler/checker.ts

@@ -15780,19 +15780,20 @@ namespace ts {
         }
 
         function checkClassForDuplicateDeclarations(node: ClassLikeDeclaration) {
-            const enum Accessor {
+            const enum Declaration {
                 Getter = 1,
                 Setter = 2,
+                Method = 4,
                 Property = Getter | Setter
             }
 
-            const instanceNames = createMap<Accessor>();
-            const staticNames = createMap<Accessor>();
+            const instanceNames = createMap<Declaration>();
+            const staticNames = createMap<Declaration>();
             for (const member of node.members) {
                 if (member.kind === SyntaxKind.Constructor) {
                     for (const param of (member as ConstructorDeclaration).parameters) {
                         if (isParameterPropertyDeclaration(param)) {
-                            addName(instanceNames, param.name, (param.name as Identifier).text, Accessor.Property);
+                            addName(instanceNames, param.name, (param.name as Identifier).text, Declaration.Property);
                         }
                     }
                 }
@@ -15804,25 +15805,34 @@ namespace ts {
                     if (memberName) {
                         switch (member.kind) {
                             case SyntaxKind.GetAccessor:
-                                addName(names, member.name, memberName, Accessor.Getter);
+                                addName(names, member.name, memberName, Declaration.Getter);
                                 break;
 
                             case SyntaxKind.SetAccessor:
-                                addName(names, member.name, memberName, Accessor.Setter);
+                                addName(names, member.name, memberName, Declaration.Setter);
                                 break;
 
                             case SyntaxKind.PropertyDeclaration:
-                                addName(names, member.name, memberName, Accessor.Property);
+                                addName(names, member.name, memberName, Declaration.Property);
+                                break;
+
+                            case SyntaxKind.MethodDeclaration:
+                                addName(names, member.name, memberName, Declaration.Method);
                                 break;
                         }
                     }
                 }
             }
 
-            function addName(names: Map<Accessor>, location: Node, name: string, meaning: Accessor) {
+            function addName(names: Map<Declaration>, location: Node, name: string, meaning: Declaration) {
                 const prev = names.get(name);
                 if (prev) {
-                    if (prev & meaning) {
+                    if (prev & Declaration.Method) {
+                        if (meaning !== Declaration.Method) {
+                            error(location, Diagnostics.Duplicate_identifier_0, getTextOfNode(location));
+                        }
+                    }
+                    else if (prev & meaning) {
                         error(location, Diagnostics.Duplicate_identifier_0, getTextOfNode(location));
                     }
                     else {

tests/baselines/reference/classWithDuplicateIdentifier.errors.txt

@@ -0,0 +1,31 @@
+tests/cases/compiler/classWithDuplicateIdentifier.ts(3,5): error TS2300: Duplicate identifier 'a'.
+tests/cases/compiler/classWithDuplicateIdentifier.ts(6,5): error TS2300: Duplicate identifier 'b'.
+tests/cases/compiler/classWithDuplicateIdentifier.ts(7,5): error TS2300: Duplicate identifier 'b'.
+tests/cases/compiler/classWithDuplicateIdentifier.ts(11,5): error TS2300: Duplicate identifier 'c'.
+tests/cases/compiler/classWithDuplicateIdentifier.ts(11,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'c' must be of type 'number', but here has type 'string'.
+
+
+==== tests/cases/compiler/classWithDuplicateIdentifier.ts (5 errors) ====
+    class C {
+        a(): number { return 0; } // error: duplicate identifier
+        a: number;
+        ~
+!!! error TS2300: Duplicate identifier 'a'.
+    }
+    class K {
+        b: number; // error: duplicate identifier
+        ~
+!!! error TS2300: Duplicate identifier 'b'.
+        b(): number { return 0; }
+        ~
+!!! error TS2300: Duplicate identifier 'b'.
+    }
+    class D {
+        c: number;
+        c: string;
+        ~
+!!! error TS2300: Duplicate identifier 'c'.
+        ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'c' must be of type 'number', but here has type 'string'.
+    }
+

tests/baselines/reference/classWithDuplicateIdentifier.js

@@ -0,0 +1,33 @@
+//// [classWithDuplicateIdentifier.ts]
+class C {
+    a(): number { return 0; } // error: duplicate identifier
+    a: number;
+}
+class K {
+    b: number; // error: duplicate identifier
+    b(): number { return 0; }
+}
+class D {
+    c: number;
+    c: string;
+}
+
+
+//// [classWithDuplicateIdentifier.js]
+var C = (function () {
+    function C() {
+    }
+    C.prototype.a = function () { return 0; }; // error: duplicate identifier
+    return C;
+}());
+var K = (function () {
+    function K() {
+    }
+    K.prototype.b = function () { return 0; };
+    return K;
+}());
+var D = (function () {
+    function D() {
+    }
+    return D;
+}());

tests/cases/compiler/classWithDuplicateIdentifier.ts

@@ -0,0 +1,12 @@
+class C {
+    a(): number { return 0; } // error: duplicate identifier
+    a: number;
+}
+class K {
+    b: number; // error: duplicate identifier
+    b(): number { return 0; }
+}
+class D {
+    c: number;
+    c: string;
+}