Merge pull request #13056 from mostafa8026/perf/12914-readable-error-on-undefined-token

perf(common): Improve error handling for undefined tokens

Author: kamilmysliwiec

packages/common/decorators/core/inject.decorator.ts

@@ -39,6 +39,12 @@ export function Inject<T = any>(
   return (target: object, key: string | symbol | undefined, index?: number) => {
     const type = token || Reflect.getMetadata('design:type', target, key);
 
+    if (!type) {
+      throw new Error(`Token is undefined at index: ${index}. This often occurs due to circular dependencies.
+Ensure there are no circular dependencies in your files or barrel files. 
+For more details, refer to https://trilon.io/blog/avoiding-circular-dependencies-in-nestjs.`);
+    }
+
     if (!isUndefined(index)) {
       let dependencies =
         Reflect.getMetadata(SELF_DECLARED_DEPS_METADATA, target) || [];

packages/common/test/decorators/inject.decorator.spec.ts

@@ -22,4 +22,14 @@ describe('@Inject', () => {
     ];
     expect(metadata).to.be.eql(expectedMetadata);
   });
+
+  it('should throw an error when token is undefined', () => {
+    const defineInvalidClass = () => {
+      class Test {
+        constructor(@Inject(undefined) invalidParam) {}
+      }
+    };
+
+    expect(defineInvalidClass).to.throw(/^Token is undefined/);
+  });
 });