From b64bb2020dbc47b0c8375ebbd407d3e1013f4fcd Mon Sep 17 00:00:00 2001
From: cm-ayf <cm.ayf2734@gmail.com>
Date: Sat, 3 Dec 2022 10:43:33 +0900
Subject: [PATCH 1/4] strictly type around code and statusCode

---
 types/index.d.ts | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/types/index.d.ts b/types/index.d.ts
index ddaadd3..de322ee 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1,4 +1,7 @@
-type CreateError = (code: string, message: string, statusCode?: number, Base?: Error) => createError.FastifyErrorConstructor
+declare function createError<C extends string, SC extends number>(code: C, message: string, statusCode: SC, Base?: Error): createError.FastifyErrorConstructor<{ code: C; statusCode: SC }>;
+declare function createError<C extends string>(code: C, message: string, statusCode?: number, Base?: Error): createError.FastifyErrorConstructor<{ code: C; }>;
+
+type CreateError = typeof createError;
 
 declare namespace createError {
   export interface FastifyError extends Error {
@@ -7,15 +10,14 @@ declare namespace createError {
     statusCode?: number;
   }
 
-  export interface FastifyErrorConstructor {
-    new(a?: any, b?: any, c?: any): FastifyError;
-    (a?: any, b?: any, c?: any): FastifyError;
-    readonly prototype: FastifyError;
+  export interface FastifyErrorConstructor<E extends {} = {}> {
+    new (a?: any, b?: any, c?: any): FastifyError & E;
+    (a?: any, b?: any, c?: any): FastifyError & E;
+    readonly prototype: FastifyError & E;
   }
 
   export const createError: CreateError
   export { createError as default }
 }
 
-declare function createError(...params: Parameters<CreateError>): ReturnType<CreateError>
 export = createError

From 59166abe68c3c557fd6cb2b596fbf0078d2b4660 Mon Sep 17 00:00:00 2001
From: cm-ayf <cm.ayf2734@gmail.com>
Date: Sat, 3 Dec 2022 10:46:13 +0900
Subject: [PATCH 2/4] add test around strictly typed code and statusCode

---
 types/index.test-d.ts | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/types/index.test-d.ts b/types/index.test-d.ts
index 54cd073..6066602 100644
--- a/types/index.test-d.ts
+++ b/types/index.test-d.ts
@@ -7,4 +7,12 @@ const err = new CustomError()
 expectType<FastifyError>(err)
 expectType<string>(err.code)
 expectType<string>(err.message)
-expectType<number>(err.statusCode!)
\ No newline at end of file
+expectType<number>(err.statusCode!)
+
+const CustomTypedError = createError('OTHER_CODE', 'message', 400)
+expectType<FastifyErrorConstructor<{ code: 'OTHER_CODE'; statusCode: 400 }>>(CustomTypedError)
+const typed = new CustomTypedError()
+expectType<FastifyError & { code: 'OTHER_CODE'; statusCode: 400 }>(typed)
+expectType<'OTHER_CODE'>(typed.code)
+expectType<string>(typed.message)
+expectType<400>(typed.statusCode)

From 2b7c57d5335d0c94a99218260485b42f6a07a2aa Mon Sep 17 00:00:00 2001
From: cm-ayf <cm.ayf2734@gmail.com>
Date: Sat, 3 Dec 2022 10:48:10 +0900
Subject: [PATCH 3/4] narrower type to test

---
 types/index.test-d.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/types/index.test-d.ts b/types/index.test-d.ts
index 6066602..37d7fc3 100644
--- a/types/index.test-d.ts
+++ b/types/index.test-d.ts
@@ -2,10 +2,10 @@ import createError, { FastifyError, FastifyErrorConstructor } from '..'
 import { expectType } from 'tsd'
 
 const CustomError = createError('ERROR_CODE', 'message')
-expectType<FastifyErrorConstructor>(CustomError)
+expectType<FastifyErrorConstructor<{ code: 'ERROR_CODE' }>>(CustomError)
 const err = new CustomError()
-expectType<FastifyError>(err)
-expectType<string>(err.code)
+expectType<FastifyError & { code: 'ERROR_CODE' }>(err)
+expectType<'ERROR_CODE'>(err.code)
 expectType<string>(err.message)
 expectType<number>(err.statusCode!)
 

From 5319190cfec04992aece6f0976e27632cda669b5 Mon Sep 17 00:00:00 2001
From: cm-ayf <cm.ayf2734@gmail.com>
Date: Wed, 7 Dec 2022 20:36:16 +0900
Subject: [PATCH 4/4] stricter generics constraint

---
 types/index.d.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/types/index.d.ts b/types/index.d.ts
index de322ee..9591a93 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -10,7 +10,7 @@ declare namespace createError {
     statusCode?: number;
   }
 
-  export interface FastifyErrorConstructor<E extends {} = {}> {
+  export interface FastifyErrorConstructor<E extends { code: string; statusCode?: number } = { code: string; statusCode?: number }> {
     new (a?: any, b?: any, c?: any): FastifyError & E;
     (a?: any, b?: any, c?: any): FastifyError & E;
     readonly prototype: FastifyError & E;