Allow to omit init arg of fetch

Author: mpppk

pkgs/typed-api-spec/src/fetch/index.t-test.ts

@@ -45,13 +45,22 @@ type ValidateUrlTestCase = [
         };
       };
     };
+    "/users2": {
+      get: {
+        headers: { "x-foo"?: string; "x-bar"?: string };
+        responses: { 200: { body: { prop: string } } };
+      };
+    };
   }>;
   (async () => {
     const f = fetch as FetchT<"", Spec>;
     {
-      // @ts-expect-error 今はinitの省略ができないが、できるようにしたい
+      // get methodが定義されており、headersが必要ない場合、Initは省略可能
       await f("/users");
 
+      // headersが定義されていても、すべて省略可能な場合はInitも省略可能
+      await f("/users2");
+
       // methodを省略した場合はgetとして扱う
       const res = await f("/users", {});
       (await res.json()).prop;
@@ -63,6 +72,31 @@ type ValidateUrlTestCase = [
     }
   })();
 }
+{
+  type Spec = DefineApiEndpoints<{
+    "/users": {
+      get: {
+        headers: { "x-foo"?: string; "Content-Type": "application/json" };
+        responses: { 200: { body: { prop: string } } };
+      };
+    };
+    "/users2": {
+      post: {
+        responses: { 200: { body: { prop: string } } };
+      };
+    };
+  }>;
+  (async () => {
+    const f = fetch as FetchT<"", Spec>;
+    {
+      // @ts-expect-error getメソッドが定義されていても、headersが要求されている場合はInitは省略できない
+      await f("/users");
+
+      // @ts-expect-error getメソッドが定義されていない場合、Initは省略できない
+      await f("/users2");
+    }
+  })();
+}
 {
   type Spec = DefineApiEndpoints<{
     "/users": {

pkgs/typed-api-spec/src/fetch/index.ts

@@ -141,6 +141,8 @@ type FetchT<UrlPrefix extends UrlPrefixPattern, E extends ApiEndpoints> = <
     : never,
   LM extends Lowercase<InputMethod>,
   Query extends ApiP<E, CandidatePaths, LM, "query">,
+  Headers extends ApiP<E, CandidatePaths, LM, "headers">,
+  Body extends ApiP<E, CandidatePaths, LM, "body">,
   Response extends ApiP<
     E,
     CandidatePaths,
@@ -154,17 +156,25 @@ type FetchT<UrlPrefix extends UrlPrefixPattern, E extends ApiEndpoints> = <
     AcceptableMethods,
     "get"
   >,
+  CanOmitMethod extends boolean = "get" extends AcceptableMethods
+    ? true
+    : false,
+  CanOmitInit extends boolean = CanOmitMethod extends true
+    ? Headers extends undefined
+      ? true
+      : Headers extends Record<string, string>
+        ? IsAllOptional<Headers> extends true
+          ? true
+          : false
+        : false
+    : false,
 >(
   input: [ValidatedUrl] extends [C.OK | QueryParameterRequiredError]
     ? Input
     : ValidatedUrl,
-  init: RequestInitT<
-    // If `get` method is defined in the spec, method can be omitted
-    "get" extends AcceptableMethods ? true : false,
-    ApiP<E, CandidatePaths, LM, "body">,
-    ApiP<E, CandidatePaths, LM, "headers">,
-    InputMethod
-  >,
+  ...args: CanOmitInit extends true
+    ? [init?: RequestInitT<CanOmitMethod, Body, Headers, InputMethod>]
+    : [init: RequestInitT<CanOmitMethod, Body, Headers, InputMethod>]
 ) => Promise<Response>;
 
 export default FetchT;