From c69961588fa7094f58347e42229fd3e849973306 Mon Sep 17 00:00:00 2001
From: PongDev <pongwiwat.dev@gmail.com>
Date: Tue, 3 Jun 2025 16:36:51 +0700
Subject: [PATCH] fix(type): config service get and getOrThrow methods return
 type

When a ConfigService type is provided, the return type should match the given type; otherwise, a compile error should occur.
---
 lib/config.service.ts              | 27 ++++++++++++++++++++-------
 tests/e2e/optional-generic.spec.ts | 28 ++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/lib/config.service.ts b/lib/config.service.ts
index 2c65b150..5b052dd6 100644
--- a/lib/config.service.ts
+++ b/lib/config.service.ts
@@ -94,7 +94,11 @@ export class ConfigService<
    * @param propertyPath
    * @param options
    */
-  get<T = K, P extends Path<T> = any, R = PathValue<T, P>>(
+  get<
+    T = K,
+    P extends Path<T> = any,
+    R extends PathValue<T, P> = PathValue<T, P>,
+  >(
     propertyPath: P,
     options: ConfigGetOptions,
   ): ValidatedResult<WasValidated, R>;
@@ -114,7 +118,11 @@ export class ConfigService<
    * @param defaultValue
    * @param options
    */
-  get<T = K, P extends Path<T> = any, R = PathValue<T, P>>(
+  get<
+    T = K,
+    P extends Path<T> = any,
+    R extends PathValue<T, P> = PathValue<T, P>,
+  >(
     propertyPath: P,
     defaultValue: NoInferType<R>,
     options: ConfigGetOptions,
@@ -171,10 +179,11 @@ export class ConfigService<
    * @param propertyPath
    * @param options
    */
-  getOrThrow<T = K, P extends Path<T> = any, R = PathValue<T, P>>(
-    propertyPath: P,
-    options: ConfigGetOptions,
-  ): Exclude<R, undefined>;
+  getOrThrow<
+    T = K,
+    P extends Path<T> = any,
+    R extends PathValue<T, P> = PathValue<T, P>,
+  >(propertyPath: P, options: ConfigGetOptions): Exclude<R, undefined>;
   /**
    * Get a configuration value (either custom configuration or process environment variable)
    * based on property path (you can use dot notation to traverse nested object, e.g. "database.host").
@@ -196,7 +205,11 @@ export class ConfigService<
    * @param defaultValue
    * @param options
    */
-  getOrThrow<T = K, P extends Path<T> = any, R = PathValue<T, P>>(
+  getOrThrow<
+    T = K,
+    P extends Path<T> = any,
+    R extends PathValue<T, P> = PathValue<T, P>,
+  >(
     propertyPath: P,
     defaultValue: NoInferType<R>,
     options: ConfigGetOptions,
diff --git a/tests/e2e/optional-generic.spec.ts b/tests/e2e/optional-generic.spec.ts
index ac8ae7d8..a63fd56a 100644
--- a/tests/e2e/optional-generic.spec.ts
+++ b/tests/e2e/optional-generic.spec.ts
@@ -69,6 +69,34 @@ describe('Optional Generic()', () => {
     expect(port).toEqual('default');
   });
 
+  it(`should compile error when return wrong type`, () => {
+    const configService =
+      moduleRef.get<ConfigService<{ PORT: string }>>(ConfigService);
+
+    // @ts-expect-error: PORT is a string, not a number. Should throw an error
+    const port: number | undefined = configService.get('PORT', { infer: true });
+
+    // @ts-expect-error: PORT is a string, not a number. Should throw an error
+    const portWithDefaultValue: number = configService.get('PORT', '', {
+      infer: true,
+    });
+  });
+
+  it(`should compile error when return wrong type (getOrThrow)`, () => {
+    const configService =
+      moduleRef.get<ConfigService<{ PORT: string }>>(ConfigService);
+
+    // @ts-expect-error: PORT is a string, not a number. Should throw an error
+    const port: number = configService.getOrThrow('PORT', {
+      infer: true,
+    });
+
+    // @ts-expect-error: PORT is a string, not a number. Should throw an error
+    const portWithDefaultValue: number = configService.getOrThrow('PORT', '', {
+      infer: true,
+    });
+  });
+
   afterEach(async () => {
     await app.close();
   });