Add type helpers only when used (#992)

Author: Loïc Fürhoff

examples/octokit-ghes-3.6-diff-to-api.ts

@@ -4,11 +4,6 @@
  */
 
 
-/** Type helpers */
-type Without<T, U> = { [P in Exclude<keyof T, keyof U>]?: never };
-type XOR<T, U> = (T | U) extends object ? (Without<T, U> & U) | (Without<U, T> & T) : T | U;
-type OneOf<T extends any[]> = T extends [infer Only] ? Only : T extends [infer A, infer B, ...infer Rest] ? OneOf<[XOR<A, B>, ...Rest]> : never;
-
 export interface paths {
   "/admin/hooks": {
     /** List global webhooks */

examples/stripe-api.ts

@@ -4,11 +4,6 @@
  */
 
 
-/** Type helpers */
-type Without<T, U> = { [P in Exclude<keyof T, keyof U>]?: never };
-type XOR<T, U> = (T | U) extends object ? (Without<T, U> & U) | (Without<U, T> & T) : T | U;
-type OneOf<T extends any[]> = T extends [infer Only] ? Only : T extends [infer A, infer B, ...infer Rest] ? OneOf<[XOR<A, B>, ...Rest]> : never;
-
 export interface paths {
   "/v1/account": {
     /** @description <p>Retrieves the details of an account.</p> */

src/index.ts

@@ -94,19 +94,10 @@ async function openapiTS(
     output.push(COMMENT_HEADER);
   }
 
-  // 2b. OneOf helper (@see https://github.com/Microsoft/TypeScript/issues/14094#issuecomment-723571692)
-  output.push(
-    "/** Type helpers */",
-    "type Without<T, U> = { [P in Exclude<keyof T, keyof U>]?: never };",
-    "type XOR<T, U> = (T | U) extends object ? (Without<T, U> & U) | (Without<U, T> & T) : T | U;",
-    "type OneOf<T extends any[]> = T extends [infer Only] ? Only : T extends [infer A, infer B, ...infer Rest] ? OneOf<[XOR<A, B>, ...Rest]> : never;",
-    ""
-  );
-
-  // 2c. options.inject
+  // 2b. options.inject
   if (options.inject) output.push(options.inject);
 
-  // 2d. root schema
+  // 2c. root schema
   const rootTypes = transformSchema(allSchemas["."].schema as OpenAPI3, ctx);
   for (const k of Object.keys(rootTypes)) {
     if (rootTypes[k] && !EMPTY_OBJECT_RE.test(rootTypes[k])) {
@@ -121,7 +112,7 @@ async function openapiTS(
     delete allSchemas["."]; // garbage collect, but also remove from next step (external)
   }
 
-  // 2e. external schemas (subschemas)
+  // 2d. external schemas (subschemas)
   const externalKeys = Object.keys(allSchemas); // root schema (".") should already be removed
   if (externalKeys.length) {
     let indentLv = 0;
@@ -198,6 +189,19 @@ async function openapiTS(
     output.push(`export type operations = Record<string, never>;`, "");
   }
 
+  // 4. OneOf type helper (@see https://github.com/Microsoft/TypeScript/issues/14094#issuecomment-723571692)
+  if (output.join("\n").includes("OneOf")) {
+    output.splice(
+      1,
+      0,
+      "/** Type helpers */",
+      "type Without<T, U> = { [P in Exclude<keyof T, keyof U>]?: never };",
+      "type XOR<T, U> = (T | U) extends object ? (Without<T, U> & U) | (Without<U, T> & T) : T | U;",
+      "type OneOf<T extends any[]> = T extends [infer Only] ? Only : T extends [infer A, infer B, ...infer Rest] ? OneOf<[XOR<A, B>, ...Rest]> : never;",
+      ""
+    );
+  }
+
   return output.join("\n");
 }
 

test/index.test.ts

@@ -7,7 +7,9 @@ const BOILERPLATE = `/**
  * Do not make direct changes to the file.
  */
 
+`;
 
+const TYPE_HELPERS = `
 /** Type helpers */
 type Without<T, U> = { [P in Exclude<keyof T, keyof U>]?: never };
 type XOR<T, U> = (T | U) extends object ? (Without<T, U> & U) | (Without<U, T> & T) : T | U;
@@ -442,6 +444,56 @@ export interface components {
 
 export type external = Record<string, never>;
 
+export type operations = Record<string, never>;
+`);
+      });
+    });
+
+    describe("OneOf type helpers", () => {
+      test("should be added only when used", async () => {
+        const generated = await openapiTS(
+          {
+            openapi: "3.1",
+            info: { title: "Test", version: "1.0" },
+            components: {
+              schemas: {
+                User: {
+                  oneOf: [
+                    {
+                      type: "object",
+                      properties: { firstName: { type: "string" } },
+                    },
+                    {
+                      type: "object",
+                      properties: { name: { type: "string" } },
+                    },
+                  ],
+                },
+              },
+            },
+          },
+          { exportType: false }
+        );
+        expect(generated).toBe(`${BOILERPLATE}${TYPE_HELPERS}
+export type paths = Record<string, never>;
+
+export interface components {
+  schemas: {
+    User: OneOf<[{
+      firstName?: string;
+    }, {
+      name?: string;
+    }]>;
+  };
+  responses: never;
+  parameters: never;
+  requestBodies: never;
+  headers: never;
+  pathItems: never;
+}
+
+export type external = Record<string, never>;
+
 export type operations = Record<string, never>;
 `);
       });