Improve error message for unserializable private and protected class members

src/compiler/diagnosticMessages.json

@@ -4212,7 +4212,7 @@
         "category": "Error",
         "code": 4092
     },
-    "Property '{0}' of exported class expression may not be private or protected.": {
+    "Property '{0}' of exported anonymous class type may not be private or protected.": {
         "category": "Error",
         "code": 4094
     },

src/compiler/transformers/declarations.ts

@@ -357,7 +357,10 @@ export function transformDeclarations(context: TransformationContext) {
     function reportPrivateInBaseOfClassExpression(propertyName: string) {
         if (errorNameNode || errorFallbackNode) {
             context.addDiagnostic(
-                createDiagnosticForNode((errorNameNode || errorFallbackNode)!, Diagnostics.Property_0_of_exported_class_expression_may_not_be_private_or_protected, propertyName),
+                addRelatedInfo(
+                    createDiagnosticForNode((errorNameNode || errorFallbackNode)!, Diagnostics.Property_0_of_exported_anonymous_class_type_may_not_be_private_or_protected, propertyName),
+                    ...(isVariableDeclaration((errorNameNode || errorFallbackNode)!.parent) ? [createDiagnosticForNode((errorNameNode || errorFallbackNode)!, Diagnostics.Add_a_type_annotation_to_the_variable_0, errorDeclarationNameWithFallback())] : []),
+                ),
             );
         }
     }

tests/baselines/reference/declarationEmitMixinPrivateProtected.errors.txt

@@ -1,9 +1,9 @@
-another.ts(11,1): error TS4094: Property '_assertIsStripped' of exported class expression may not be private or protected.
-another.ts(11,1): error TS4094: Property '_onDispose' of exported class expression may not be private or protected.
-first.ts(12,1): error TS4094: Property '_assertIsStripped' of exported class expression may not be private or protected.
-first.ts(12,1): error TS4094: Property '_onDispose' of exported class expression may not be private or protected.
-first.ts(13,14): error TS4094: Property '_assertIsStripped' of exported class expression may not be private or protected.
-first.ts(13,14): error TS4094: Property '_onDispose' of exported class expression may not be private or protected.
+another.ts(11,1): error TS4094: Property '_assertIsStripped' of exported anonymous class type may not be private or protected.
+another.ts(11,1): error TS4094: Property '_onDispose' of exported anonymous class type may not be private or protected.
+first.ts(12,1): error TS4094: Property '_assertIsStripped' of exported anonymous class type may not be private or protected.
+first.ts(12,1): error TS4094: Property '_onDispose' of exported anonymous class type may not be private or protected.
+first.ts(13,14): error TS4094: Property '_assertIsStripped' of exported anonymous class type may not be private or protected.
+first.ts(13,14): error TS4094: Property '_onDispose' of exported anonymous class type may not be private or protected.
 
 
 ==== first.ts (4 errors) ====
@@ -20,14 +20,14 @@ first.ts(13,14): error TS4094: Property '_onDispose' of exported class expressio
     // No error, but definition is wrong. 
     export default mix(DisposableMixin);
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS4094: Property '_assertIsStripped' of exported class expression may not be private or protected.
+!!! error TS4094: Property '_assertIsStripped' of exported anonymous class type may not be private or protected.
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS4094: Property '_onDispose' of exported class expression may not be private or protected.
+!!! error TS4094: Property '_onDispose' of exported anonymous class type may not be private or protected.
     export class Monitor extends mix(DisposableMixin) {
                  ~~~~~~~
-!!! error TS4094: Property '_assertIsStripped' of exported class expression may not be private or protected.
+!!! error TS4094: Property '_assertIsStripped' of exported anonymous class type may not be private or protected.
                  ~~~~~~~
-!!! error TS4094: Property '_onDispose' of exported class expression may not be private or protected.
+!!! error TS4094: Property '_onDispose' of exported anonymous class type may not be private or protected.
         protected _onDispose() {
         }
     }
@@ -45,9 +45,9 @@ first.ts(13,14): error TS4094: Property '_onDispose' of exported class expressio
 
     export default class extends mix(DisposableMixin) {
     ~~~~~~
-!!! error TS4094: Property '_assertIsStripped' of exported class expression may not be private or protected.
+!!! error TS4094: Property '_assertIsStripped' of exported anonymous class type may not be private or protected.
     ~~~~~~
-!!! error TS4094: Property '_onDispose' of exported class expression may not be private or protected.
+!!! error TS4094: Property '_onDispose' of exported anonymous class type may not be private or protected.
         protected _onDispose() {
         }
     }

tests/baselines/reference/emitClassExpressionInDeclarationFile2.errors.txt

@@ -1,15 +1,17 @@
-emitClassExpressionInDeclarationFile2.ts(1,12): error TS4094: Property 'p' of exported class expression may not be private or protected.
-emitClassExpressionInDeclarationFile2.ts(1,12): error TS4094: Property 'ps' of exported class expression may not be private or protected.
-emitClassExpressionInDeclarationFile2.ts(16,17): error TS4094: Property 'property' of exported class expression may not be private or protected.
-emitClassExpressionInDeclarationFile2.ts(23,14): error TS4094: Property 'property' of exported class expression may not be private or protected.
+emitClassExpressionInDeclarationFile2.ts(1,12): error TS4094: Property 'p' of exported anonymous class type may not be private or protected.
+emitClassExpressionInDeclarationFile2.ts(1,12): error TS4094: Property 'ps' of exported anonymous class type may not be private or protected.
+emitClassExpressionInDeclarationFile2.ts(16,17): error TS4094: Property 'property' of exported anonymous class type may not be private or protected.
+emitClassExpressionInDeclarationFile2.ts(23,14): error TS4094: Property 'property' of exported anonymous class type may not be private or protected.
 
 
 ==== emitClassExpressionInDeclarationFile2.ts (4 errors) ====
     export var noPrivates = class {
                ~~~~~~~~~~
-!!! error TS4094: Property 'p' of exported class expression may not be private or protected.
+!!! error TS4094: Property 'p' of exported anonymous class type may not be private or protected.
+!!! related TS9027 emitClassExpressionInDeclarationFile2.ts:1:12: Add a type annotation to the variable noPrivates.
                ~~~~~~~~~~
-!!! error TS4094: Property 'ps' of exported class expression may not be private or protected.
+!!! error TS4094: Property 'ps' of exported anonymous class type may not be private or protected.
+!!! related TS9027 emitClassExpressionInDeclarationFile2.ts:1:12: Add a type annotation to the variable noPrivates.
         static getTags() { }
         tags() { }
         private static ps = -1
@@ -26,7 +28,7 @@ emitClassExpressionInDeclarationFile2.ts(23,14): error TS4094: Property 'propert
     export type Constructor<T> = new(...args: any[]) => T;
     export function WithTags<T extends Constructor<FooItem>>(Base: T) {
                     ~~~~~~~~
-!!! error TS4094: Property 'property' of exported class expression may not be private or protected.
+!!! error TS4094: Property 'property' of exported anonymous class type may not be private or protected.
         return class extends Base {
             static getTags(): void { }
             tags(): void { }
@@ -35,7 +37,7 @@ emitClassExpressionInDeclarationFile2.ts(23,14): error TS4094: Property 'propert
 
     export class Test extends WithTags(FooItem) {}
                  ~~~~
-!!! error TS4094: Property 'property' of exported class expression may not be private or protected.
+!!! error TS4094: Property 'property' of exported anonymous class type may not be private or protected.
 
     const test = new Test();