fix(transformer): Ensure mocked interfaces don't extend themselves infinitely if passed as generic argument (#312)

* fix(transformer): Ensure mocked interfaces don't extend themselves infinitely if passed as generic argument

* chore(docs): Add circular generics to types-not-supported.mdx and warn about its use

Co-authored-by: Vittorio Guerriero <[email protected]>

Author: martinjlowm

src/transformer/genericDeclaration/genericDeclaration.ts

@@ -2,6 +2,8 @@ import * as ts from 'typescript';
 import { GetDescriptor } from '../descriptor/descriptor';
 import { TypescriptHelper } from '../descriptor/helper/helper';
 import { TypescriptCreator } from '../helper/creator';
+import { TransformerLogger } from '../logger/transformerLogger';
+import { MockDefiner } from '../mockDefiner/mockDefiner';
 import { MockIdentifierGenericParameterIds, MockIdentifierGenericParameterValue } from '../mockIdentifier/mockIdentifier';
 import { Scope } from '../scope/scope';
 import { IGenericDeclaration } from './genericDeclaration.interface';
@@ -86,6 +88,16 @@ export function GenericDeclaration(scope: Scope): IGenericDeclaration {
 
         if (ts.isTypeReferenceNode(genericNode)) {
           const typeParameterDeclaration: ts.Declaration = TypescriptHelper.GetDeclarationFromNode(genericNode.typeName);
+
+          const isExtendingItself: boolean = MockDefiner.instance.getDeclarationKeyMap(typeParameterDeclaration) === declarationKey;
+          if (isExtendingItself) {
+            // FIXME: Currently, circular generics aren't supported. See
+            // https://github.com/Typescript-TDD/ts-auto-mock/pull/312 for more
+            // details.
+            TransformerLogger().circularGenericNotSupported(genericNode.getText());
+            return acc;
+          }
+
           if (ts.isTypeParameterDeclaration(typeParameterDeclaration)) {
             addGenericParameterToExisting(
               extensionDeclarationTypeParameters[index],

src/transformer/logger/transformerLogger.ts

@@ -4,6 +4,7 @@ import { ILogger } from '../../logger/logger.interface';
 let logger: ILogger;
 
 export interface TransformerLogger {
+  circularGenericNotSupported(nodeName: string): void;
   unexpectedCreateMock(mockFileName: string, expectedFileName: string): void;
   typeNotSupported(type: string): void;
   typeOfFunctionCallNotFound(node: string): void;
@@ -13,6 +14,12 @@ export function TransformerLogger(): TransformerLogger {
   logger = logger || Logger('Transformer');
 
   return {
+    circularGenericNotSupported(nodeName: string): void {
+      logger.warning(
+        `Found a circular generic of \`${nodeName}' and such generics are currently not supported. ` +
+          'The generated mock will be incomplete.',
+      );
+    },
     unexpectedCreateMock(mockFileName: string, expectedFileName: string): void {
       logger.warning(`I\'ve found a mock creator but it comes from a different folder
             found: ${mockFileName}

src/transformer/mockFactoryCall/mockFactoryCall.ts

@@ -116,7 +116,8 @@ function addFromDeclarationExtensions(declaration: GenericDeclarationSupported,
           declarationKey,
           extensionDeclaration as GenericDeclarationSupported,
           extensionDeclarationKey,
-          extension);
+          extension,
+        );
 
         addFromDeclarationExtensions(extensionDeclaration as GenericDeclarationSupported, extensionDeclarationKey, genericDeclaration);
       });

test/transformer/descriptor/generic/extends.test.ts

@@ -244,4 +244,16 @@ describe('for generic', () => {
     });
   });
 
+  describe('with circular', () => {
+    interface A extends ClassWithGenerics<A> {
+      b: number;
+    }
+
+    it('should avoid infinite extension', () => {
+      const properties: A = createMock<A>();
+      expect(properties.a).toBeDefined();
+      expect(properties.b).toBe(0);
+    });
+  });
+
 });

ui/src/views/types-not-supported.mdx

@@ -68,4 +68,30 @@ Unfortunately this functionality doesnt work yet because when getting properties
 a mapped type typescript returns a different type of property that is difficult to mock.
 
 There is a branch created with a working version but it needs more investigation because the implementation is not readable and it may cause more issues
-[link](https://github.com/Typescript-TDD/ts-auto-mock/tree/feature/extends-mapped-type)
+[link](https://github.com/Typescript-TDD/ts-auto-mock/tree/feature/extends-mapped-type)
+
+
+## Circular Generics
+
+```ts
+class C<T> {
+  public propC: T
+  public test: string
+}
+
+class A extends C<A> {
+  public propA: number
+}
+const a: A = createMock<A>();
+
+// This will fail because we will not support generics of the same type.
+expect(a.propC.propC.test).toBe("");
+```
+
+These are discussed here:
+[link](https://github.com/Typescript-TDD/ts-auto-mock/pull/312). As of this
+writing, the problem with circular generics is that the generated AST will
+circle `A` over and over, and result in an infinite nested tree of declaration
+references. The intended behavior is to have the first back-reference stored
+elsewhere in the generated output and let it reference itself, making the
+runtime a lazy-evaluated sequence of getters.