do not crash if overloads cannot be merged under one symbol

src/compiler/checker.ts

@@ -11352,11 +11352,15 @@ namespace ts {
                         const errorNode: Node = (<FunctionLikeDeclaration>subsequentNode).name || subsequentNode;
                         // TODO(jfreeman): These are methods, so handle computed name case
                         if (node.name && (<FunctionLikeDeclaration>subsequentNode).name && (<Identifier>node.name).text === (<Identifier>(<FunctionLikeDeclaration>subsequentNode).name).text) {
-                            // the only situation when this is possible (same kind\same name but different symbol) - mixed static and instance class members
                             Debug.assert(node.kind === SyntaxKind.MethodDeclaration || node.kind === SyntaxKind.MethodSignature);
-                            Debug.assert((node.flags & NodeFlags.Static) !== (subsequentNode.flags & NodeFlags.Static));
-                            const diagnostic = node.flags & NodeFlags.Static ? Diagnostics.Function_overload_must_be_static : Diagnostics.Function_overload_must_not_be_static;
-                            error(errorNode, diagnostic);
+                            // we can get here in two cases
+                            // 1. mixed static and instance class members
+                            // 2. something with the same name was defined before the set of overloads that prevents them from merging
+                            // here we'll report error only for the first case since for second we should already report error in binder 
+                            if ((node.flags & NodeFlags.Static) !== (subsequentNode.flags & NodeFlags.Static)) {
+                                const diagnostic = node.flags & NodeFlags.Static ? Diagnostics.Function_overload_must_be_static : Diagnostics.Function_overload_must_not_be_static;
+                                error(errorNode, diagnostic);
+                            }
                             return;
                         }
                         else if (nodeIsPresent((<FunctionLikeDeclaration>subsequentNode).body)) {

tests/baselines/reference/mixedStaticAndInstanceClassMembers.errors.txt

@@ -0,0 +1,27 @@
+tests/cases/compiler/mixedStaticAndInstanceClassMembers.ts(4,5): error TS2387: Function overload must be static.
+tests/cases/compiler/mixedStaticAndInstanceClassMembers.ts(12,12): error TS2388: Function overload must not be static.
+tests/cases/compiler/mixedStaticAndInstanceClassMembers.ts(13,5): error TS2387: Function overload must be static.
+
+
+==== tests/cases/compiler/mixedStaticAndInstanceClassMembers.ts (3 errors) ====
+    class A {
+        f() {}
+        static m1 (a: string): void;
+        m1 (a: number): void;
+        ~~
+!!! error TS2387: Function overload must be static.
+        m1 (a: any): void {
+        }
+    }
+    
+    class B {
+        f() {}
+        m1 (a: string): void;
+        static m1 (a: number): void;
+               ~~
+!!! error TS2388: Function overload must not be static.
+        m1 (a: any): void {
+        ~~
+!!! error TS2387: Function overload must be static.
+        }
+    }

tests/baselines/reference/mixedStaticAndInstanceClassMembers.js

@@ -0,0 +1,34 @@
+//// [mixedStaticAndInstanceClassMembers.ts]
+class A {
+    f() {}
+    static m1 (a: string): void;
+    m1 (a: number): void;
+    m1 (a: any): void {
+    }
+}
+
+class B {
+    f() {}
+    m1 (a: string): void;
+    static m1 (a: number): void;
+    m1 (a: any): void {
+    }
+}
+
+//// [mixedStaticAndInstanceClassMembers.js]
+var A = (function () {
+    function A() {
+    }
+    A.prototype.f = function () { };
+    A.prototype.m1 = function (a) {
+    };
+    return A;
+})();
+var B = (function () {
+    function B() {
+    }
+    B.prototype.f = function () { };
+    B.prototype.m1 = function (a) {
+    };
+    return B;
+})();

tests/baselines/reference/nonMergedDeclarationsAndOverloads.errors.txt

@@ -0,0 +1,23 @@
+tests/cases/compiler/nonMergedDeclarationsAndOverloads.ts(2,5): error TS2300: Duplicate identifier 'm1'.
+tests/cases/compiler/nonMergedDeclarationsAndOverloads.ts(4,5): error TS2300: Duplicate identifier 'm1'.
+tests/cases/compiler/nonMergedDeclarationsAndOverloads.ts(5,5): error TS2300: Duplicate identifier 'm1'.
+tests/cases/compiler/nonMergedDeclarationsAndOverloads.ts(6,5): error TS2300: Duplicate identifier 'm1'.
+
+
+==== tests/cases/compiler/nonMergedDeclarationsAndOverloads.ts (4 errors) ====
+    class A {
+        m1: string;
+        ~~
+!!! error TS2300: Duplicate identifier 'm1'.
+        f() {}
+        m1 (a: string): void;
+        ~~
+!!! error TS2300: Duplicate identifier 'm1'.
+        m1 (a: number): void;
+        ~~
+!!! error TS2300: Duplicate identifier 'm1'.
+        m1 (a: any): void {
+        ~~
+!!! error TS2300: Duplicate identifier 'm1'.
+        }
+    }

tests/baselines/reference/nonMergedDeclarationsAndOverloads.js

@@ -0,0 +1,19 @@
+//// [nonMergedDeclarationsAndOverloads.ts]
+class A {
+    m1: string;
+    f() {}
+    m1 (a: string): void;
+    m1 (a: number): void;
+    m1 (a: any): void {
+    }
+}
+
+//// [nonMergedDeclarationsAndOverloads.js]
+var A = (function () {
+    function A() {
+    }
+    A.prototype.f = function () { };
+    A.prototype.m1 = function (a) {
+    };
+    return A;
+})();

tests/cases/compiler/mixedStaticAndInstanceClassMembers.ts

@@ -0,0 +1,15 @@
+class A {
+    f() {}
+    static m1 (a: string): void;
+    m1 (a: number): void;
+    m1 (a: any): void {
+    }
+}
+
+class B {
+    f() {}
+    m1 (a: string): void;
+    static m1 (a: number): void;
+    m1 (a: any): void {
+    }
+}

tests/cases/compiler/nonMergedDeclarationsAndOverloads.ts

@@ -0,0 +1,8 @@
+class A {
+    m1: string;
+    f() {}
+    m1 (a: string): void;
+    m1 (a: number): void;
+    m1 (a: any): void {
+    }
+}