do not crash when variable and function declarations collide

Author: vladima

src/compiler/checker.ts

@@ -11172,12 +11172,14 @@ namespace ts {
                         let 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) {
-                            Debug.assert(node.kind === SyntaxKind.MethodDeclaration || node.kind === SyntaxKind.MethodSignature);
+                            const reportError =
+                                (node.kind === SyntaxKind.MethodDeclaration || node.kind === SyntaxKind.MethodSignature) &&
+                                (node.flags & NodeFlags.Static) !== (subsequentNode.flags & NodeFlags.Static);
                             // 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)) {
+                            if (reportError) {
                                 const diagnostic = node.flags & NodeFlags.Static ? Diagnostics.Function_overload_must_be_static : Diagnostics.Function_overload_must_not_be_static;
                                 error(errorNode, diagnostic);
                             }

tests/baselines/reference/nonMergedOverloads.errors.txt

@@ -0,0 +1,20 @@
+tests/cases/compiler/nonMergedOverloads.ts(1,5): error TS2300: Duplicate identifier 'f'.
+tests/cases/compiler/nonMergedOverloads.ts(3,17): error TS1148: Cannot compile modules unless the '--module' flag is provided.
+tests/cases/compiler/nonMergedOverloads.ts(3,17): error TS2300: Duplicate identifier 'f'.
+tests/cases/compiler/nonMergedOverloads.ts(4,17): error TS2300: Duplicate identifier 'f'.
+
+
+==== tests/cases/compiler/nonMergedOverloads.ts (4 errors) ====
+    var f = 10;
+        ~
+!!! error TS2300: Duplicate identifier 'f'.
+    
+    export function f();
+                    ~
+!!! error TS1148: Cannot compile modules unless the '--module' flag is provided.
+                    ~
+!!! error TS2300: Duplicate identifier 'f'.
+    export function f() {
+                    ~
+!!! error TS2300: Duplicate identifier 'f'.
+    }

tests/baselines/reference/nonMergedOverloads.js

@@ -0,0 +1,12 @@
+//// [nonMergedOverloads.ts]
+var f = 10;
+
+export function f();
+export function f() {
+}
+
+//// [nonMergedOverloads.js]
+var f = 10;
+function f() {
+}
+exports.f = f;

tests/cases/compiler/nonMergedOverloads.ts

@@ -0,0 +1,5 @@
+var f = 10;
+
+export function f();
+export function f() {
+}