Fix #4506: Remove assert to allow for invalid patterns already flagged erlier by the checker

Author: mhegazy

src/compiler/checker.ts

@@ -2429,7 +2429,7 @@ namespace ts {
                         return false;
 
                     default:
-                        Debug.fail("isDeclarationVisible unknown: SyntaxKind: " + node.kind);
+                        return false;
                 }
             }
         }

tests/baselines/reference/declarationEmit_invalidExport.errors.txt

@@ -0,0 +1,19 @@
+tests/cases/compiler/declarationEmit_invalidExport.ts(3,3): error TS7027: Unreachable code detected.
+tests/cases/compiler/declarationEmit_invalidExport.ts(5,30): error TS4081: Exported type alias 'MyClass' has or is using private name 'myClass'.
+tests/cases/compiler/declarationEmit_invalidExport.ts(6,1): error TS1128: Declaration or statement expected.
+
+
+==== tests/cases/compiler/declarationEmit_invalidExport.ts (3 errors) ====
+    
+    if (false) {
+      export var myClass = 0;
+      ~~~~~~
+!!! error TS7027: Unreachable code detected.
+    }
+    export type MyClass = typeof myClass;
+                                 ~~~~~~~
+!!! error TS4081: Exported type alias 'MyClass' has or is using private name 'myClass'.
+    }
+    ~
+!!! error TS1128: Declaration or statement expected.
+    

tests/baselines/reference/declarationEmit_invalidExport.js

@@ -0,0 +1,14 @@
+//// [declarationEmit_invalidExport.ts]
+
+if (false) {
+  export var myClass = 0;
+}
+export type MyClass = typeof myClass;
+}
+
+
+//// [declarationEmit_invalidExport.js]
+"use strict";
+if (false) {
+    exports.myClass = 0;
+}

tests/cases/compiler/declarationEmit_invalidExport.ts

@@ -0,0 +1,7 @@
+// @declaration: true
+
+if (false) {
+  export var myClass = 0;
+}
+export type MyClass = typeof myClass;
+}