queryが定義されているかに応じてInputの型を絞り込む (#81)

Author: mpppk

examples/express/fetch.ts

@@ -10,7 +10,7 @@ const JSONT = JSON as JSONT;
 
 const main = async () => {
   {
-    const path = `${origin}/users`;
+    const path = `${origin}/users?page=1`;
     const method = "get";
     const res = await fetchT(path, { method });
     switch (res.status) {
@@ -32,7 +32,7 @@ const main = async () => {
   }
   {
     // case-insensitive method example
-    await fetchT(`${origin}/users`, { method: "GET" });
+    await fetchT(`${origin}/users?page=1`, { method: "GET" });
   }
   {
     // query parameter example

src/common/spec.ts

@@ -95,9 +95,9 @@ export type ApiP<
     ? // eslint-disable-next-line @typescript-eslint/no-explicit-any
       E[Path][M][P] extends Record<string, any>
       ? E[Path][M][P]
-      : never
-    : never
-  : never;
+      : undefined
+    : undefined
+  : undefined;
 
 export type ApiHasP<
   E extends ApiEndpoints,

src/fetch/index.t-test.ts

@@ -84,16 +84,17 @@ import JSONT from "../json";
     }
 
     {
-      // AsJsonApiを利用していない場合、Content-Typeがapplication/jsonでなくてもエラーにならない
-      await f2("/users", {});
-    }
-
-    {
+      // @ts-expect-error queryが定義されていないSpecに対してクエリパラメータを指定した場合は型エラー
       await f("/users?a=1", {
         headers: { "Content-Type": "application/json" },
       });
     }
 
+    {
+      // AsJsonApiを利用していない場合、Content-Typeがapplication/jsonでなくてもエラーにならない
+      await f2("/users", {});
+    }
+
     {
       const res = await f("/users", {
         method: "post",
@@ -155,20 +156,32 @@ import JSONT from "../json";
         resBody: {
           200: { prop: string };
         };
+        query: {
+          state: boolean;
+        };
       };
     };
   }>;
   (async () => {
     const basePath = "/api/projects/:projectName/workflow";
     const f = fetch as FetchT<typeof basePath, Spec>;
-    const res = await f(
-      `/api/projects/projectA/workflow/packages/list?state=true`,
+    {
+      const res = await f(
+        `/api/projects/projectA/workflow/packages/list?state=true`,
+        {
+          headers: { Cookie: "a=b" },
+        },
+      );
+      if (res.ok) {
+        (await res.json()).prop;
+      }
+
       {
-        headers: { Cookie: "a=b" },
-      },
-    );
-    if (res.ok) {
-      (await res.json()).prop;
+        // @ts-expect-error queryが定義されているSpecに対してクエリパラメータを指定しなかった場合は型エラー
+        f(`/api/projects/projectA/workflow/packages/list`, {
+          headers: { Cookie: "a=b" },
+        });
+      }
     }
   })();
 }

src/fetch/index.ts

@@ -2,6 +2,7 @@ import {
   ApiEndpoints,
   ApiHasP,
   ApiP,
+  ApiResponses,
   CaseInsensitiveMethod,
   FilterNever,
   MatchedPatterns,
@@ -11,14 +12,15 @@ import {
   ParseURL,
   PathToUrlParamPattern,
   Replace,
+  StatusCode,
 } from "../common";
 import { UrlPrefixPattern, ToUrlParamPattern } from "../common";
 import { TypedString } from "../json";
 
 export type RequestInitT<
   InputMethod extends CaseInsensitiveMethod,
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  Body extends Record<string, any> | never,
+  Body extends Record<string, any> | undefined,
   HeadersObj extends Record<string, string> | undefined,
 > = Omit<RequestInit, "method" | "body" | "headers"> & {
   method?: InputMethod;
@@ -34,9 +36,9 @@ export type RequestInitT<
  * FetchT is a type for window.fetch like function but more strict type information
  */
 type FetchT<UrlPrefix extends UrlPrefixPattern, E extends ApiEndpoints> = <
-  Input extends
-    | ToUrlParamPattern<`${UrlPrefix}${keyof E & string}`>
-    | `${ToUrlParamPattern<`${UrlPrefix}${keyof E & string}`>}?${string}`,
+  Input extends Query extends undefined
+    ? ToUrlParamPattern<`${UrlPrefix}${keyof E & string}`>
+    : `${ToUrlParamPattern<`${UrlPrefix}${keyof E & string}`>}?${string}`,
   InputPath extends PathToUrlParamPattern<
     NormalizePath<
       ParseURL<Replace<Input, ToUrlParamPattern<UrlPrefix>, "">>["path"]
@@ -45,6 +47,18 @@ type FetchT<UrlPrefix extends UrlPrefixPattern, E extends ApiEndpoints> = <
   CandidatePaths extends string = MatchedPatterns<InputPath, keyof E & string>,
   InputMethod extends CaseInsensitiveMethod = "get",
   M extends Method = Lowercase<InputMethod>,
+  Query extends ApiP<E, CandidatePaths, M, "query"> = ApiP<
+    E,
+    CandidatePaths,
+    M,
+    "query"
+  >,
+  ResBody extends ApiP<E, CandidatePaths, M, "resBody"> = ApiP<
+    E,
+    CandidatePaths,
+    M,
+    "resBody"
+  >,
 >(
   input: Input,
   init: ApiHasP<E, CandidatePaths, M> extends true
@@ -60,6 +74,10 @@ type FetchT<UrlPrefix extends UrlPrefixPattern, E extends ApiEndpoints> = <
             ApiP<E, CandidatePaths, M, "headers">
           >
         | undefined,
-) => Promise<MergeApiResponses<ApiP<E, CandidatePaths, M, "resBody">>>;
+) => Promise<
+  MergeApiResponses<
+    ResBody extends ApiResponses ? ResBody : Record<StatusCode, never>
+  >
+>;
 
 export default FetchT;