Issue an error when a derived class precedes its base class

Author: RyanCavanaugh

src/compiler/checker.ts

@@ -15179,6 +15179,12 @@ namespace ts {
                     checkTypeAssignableTo(staticType, getTypeWithoutSignatures(staticBaseType), node.name || node,
                         Diagnostics.Class_static_side_0_incorrectly_extends_base_class_static_side_1);
 
+                    if (baseType.symbol.valueDeclaration && !(baseType.symbol.valueDeclaration.flags & NodeFlags.Ambient)) {
+                        if (!isBlockScopedNameDeclaredBeforeUse(baseType.symbol.valueDeclaration, node)) {
+                            error(baseTypeNode, Diagnostics.A_class_must_be_declared_after_its_base_class);
+                        }
+                    }
+
                     if (!(staticBaseType.symbol && staticBaseType.symbol.flags & SymbolFlags.Class)) {
                         // When the static base type is a "class-like" constructor function (but not actually a class), we verify
                         // that all instantiated base constructor signatures return the same type. We can simply compare the type

src/compiler/diagnosticMessages.json

@@ -1923,6 +1923,10 @@
         "category": "Error",
         "code": 2685
     },
+    "A class must be declared after its base class.": {
+        "category": "Error",
+        "code": 2686
+    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000

tests/baselines/reference/baseTypeWrappingInstantiationChain.errors.txt

@@ -0,0 +1,35 @@
+tests/cases/compiler/baseTypeWrappingInstantiationChain.ts(1,21): error TS2686: A class must be declared after its base class.
+tests/cases/compiler/baseTypeWrappingInstantiationChain.ts(12,25): error TS2686: A class must be declared after its base class.
+
+
+==== tests/cases/compiler/baseTypeWrappingInstantiationChain.ts (2 errors) ====
+    class C<T1> extends CBase<T1> {
+                        ~~~~~~~~~
+!!! error TS2686: A class must be declared after its base class.
+        public works() {
+            new CBaseBase<Wrapper<T1>>(this);
+        }
+        public alsoWorks() {
+            new CBase<T1>(this); // Should not error, parameter is of type Parameter<Wrapper<T1>>
+        }
+    
+        public method(t: Wrapper<T1>) { }
+    }
+    
+    class CBase<T2> extends CBaseBase<Wrapper<T2>> {
+                            ~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2686: A class must be declared after its base class.
+    
+    }
+    
+    class CBaseBase<T3> {
+        constructor(x: Parameter<T3>) { }
+    }
+    
+    class Parameter<T4> {
+        method(t: T4) { }
+    }
+    
+    class Wrapper<T5> {
+        property: T5;
+    }

tests/baselines/reference/baseTypeWrappingInstantiationChain.symbols

@@ -0,0 +1,25 @@
+tests/cases/conformance/internalModules/importDeclarations/circularImportAlias.ts(5,28): error TS2686: A class must be declared after its base class.
+
+
+==== tests/cases/conformance/internalModules/importDeclarations/circularImportAlias.ts (1 errors) ====
+    // expected no error
+    
+    module B {
+        export import a = A;
+        export class D extends a.C {
+                               ~~~
+!!! error TS2686: A class must be declared after its base class.
+            id: number;
+        }
+    }
+    
+    module A {
+        export class C { name: string }
+        export import b = B;
+    }
+    
+    var c: { name: string };
+    var c = new B.a.C();
+    
+    
+    

tests/baselines/reference/baseTypeWrappingInstantiationChain.types

@@ -0,0 +1,15 @@
+tests/cases/conformance/classes/classExpressions/classExpression3.ts(1,23): error TS2686: A class must be declared after its base class.
+tests/cases/conformance/classes/classExpressions/classExpression3.ts(1,37): error TS2686: A class must be declared after its base class.
+
+
+==== tests/cases/conformance/classes/classExpressions/classExpression3.ts (2 errors) ====
+    let C = class extends class extends class { a = 1 } { b = 2 } { c = 3 };
+                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2686: A class must be declared after its base class.
+                                        ~~~~~~~~~~~~~~~
+!!! error TS2686: A class must be declared after its base class.
+    let c = new C();
+    c.a;
+    c.b;
+    c.c;
+