Merge pull request #123 from millsp/perf/types/deep-mock

perf(types): prevent immediate deep and circular resolution for deep mock

src/Mock.ts

@@ -30,22 +30,35 @@ export interface CalledWithMock<T, Y extends any[]> extends jest.Mock<T, Y> {
     calledWith: (...args: Y | MatchersOrLiterals<Y>) => jest.Mock<T, Y>;
 }
 
-export type MockProxy<T> = {
-    [K in keyof T]: T[K] extends (...args: infer A) => infer B ? CalledWithMock<B, A> : T[K];
-} &
-    T;
+export type _MockProxy<T> = {
+    [K in keyof T]: T[K] extends (...args: infer A) => infer B
+                    ? T[K] & CalledWithMock<B, A>
+                    : T[K];
+};
+
+export type MockProxy<T> = _MockProxy<T> & T;
 
-export type DeepMockProxy<T> = {
+export type _DeepMockProxy<T> = {
     // This supports deep mocks in the else branch
-    [K in keyof T]: T[K] extends (...args: infer A) => infer B ? CalledWithMock<B, A> : DeepMockProxy<T[K]>;
-} &
-    T;
+    [K in keyof T]: T[K] extends (...args: infer A) => infer B
+                    ? T[K] & CalledWithMock<B, A>
+                    : T[K] & _DeepMockProxy<T[K]>;
+};
 
-export type DeepMockProxyWithFuncPropSupport<T> = {
+// we intersect with T here instead of on the mapped type above to
+// prevent immediate type resolution on a recursive type, this will
+// help to improve performance for deeply nested recursive mocking
+// at the same time, this intersection preserves private properties
+export type DeepMockProxy<T> = _DeepMockProxy<T> & T;
+
+export type _DeepMockProxyWithFuncPropSupport<T> = {
     // This supports deep mocks in the else branch
-    [K in keyof T]: T[K] extends (...args: infer A) => infer B ? CalledWithMock<B, A> & DeepMockProxy<T[K]> : DeepMockProxy<T[K]>;
-} &
-    T;
+    [K in keyof T]: T[K] extends (...args: infer A) => infer B
+                    ? CalledWithMock<B, A> & DeepMockProxy<T[K]>
+                    : DeepMockProxy<T[K]>;
+};
+
+export type DeepMockProxyWithFuncPropSupport<T> = _DeepMockProxyWithFuncPropSupport<T> & T;
 
 export interface MockOpts {
     deep?: boolean;