Reports error if class declaration appears before extended type declaration

Fixes #4341

Author: sheetalkamat

src/compiler/checker.ts

@@ -12616,6 +12616,10 @@ namespace ts {
                         }
                     }
                     checkKindsOfPropertyMemberOverrides(type, baseType);
+
+                    if (!isDefinedBefore(baseType.symbol.declarations[0], node)) {
+                        error(getClassExtendsHeritageClauseElement(node), Diagnostics.Base_expression_references_type_before_it_is_declared);
+                    }
                 }
             }
 

src/compiler/diagnosticInformationMap.generated.ts

@@ -427,6 +427,7 @@ namespace ts {
         Cannot_emit_namespaced_JSX_elements_in_React: { code: 2650, category: DiagnosticCategory.Error, key: "Cannot emit namespaced JSX elements in React" },
         A_member_initializer_in_a_const_enum_declaration_cannot_reference_members_declared_after_it_including_members_defined_in_other_const_enums: { code: 2651, category: DiagnosticCategory.Error, key: "A member initializer in a 'const' enum declaration cannot reference members declared after it, including members defined in other 'const' enums." },
         Merged_declaration_0_cannot_include_a_default_export_declaration_Consider_adding_a_separate_export_default_0_declaration_instead: { code: 2652, category: DiagnosticCategory.Error, key: "Merged declaration '{0}' cannot include a default export declaration. Consider adding a separate 'export default {0}' declaration instead." },
+        Base_expression_references_type_before_it_is_declared: { code: 2653, category: DiagnosticCategory.Error, key: "Base expression references type before it is declared." },
         Import_declaration_0_is_using_private_name_1: { code: 4000, category: DiagnosticCategory.Error, key: "Import declaration '{0}' is using private name '{1}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_private_name_1: { code: 4002, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using private name '{1}'." },
         Type_parameter_0_of_exported_interface_has_or_is_using_private_name_1: { code: 4004, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported interface has or is using private name '{1}'." },

src/compiler/diagnosticMessages.json

@@ -1697,6 +1697,10 @@
         "category": "Error",
         "code": 2652
     },
+    "Base expression references type before it is declared.": {
+        "category": "Error",
+        "code": 2653
+    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000

tests/baselines/reference/baseClassOutOfOrder.errors.txt

@@ -0,0 +1,17 @@
+tests/cases/compiler/baseClassOutOfOrder.ts(1,17): error TS2653: Base expression references type before it is declared.
+
+
+==== tests/cases/compiler/baseClassOutOfOrder.ts (1 errors) ====
+    class B extends A {
+                    ~
+!!! error TS2653: Base expression references type before it is declared.
+        constructor(msg: string) {
+            super(msg);
+        }
+    }
+    
+    class A {
+        constructor(public msg: string) {
+    
+        }
+    }