Watch code generation overlays for hot regeneration

src/typescript-generator/code-generator.ts

@@ -223,33 +223,35 @@ export class CodeGenerator extends EventTarget {
   }
 
   /**
-   * Starts watching the OpenAPI document for changes.
+   * Starts watching the OpenAPI document and any overlay files for changes.
    *
-   * Has no effect when `openApiPath` is a URL (HTTP sources are not watched).
+   * Has no effect when neither source is watchable (for example, an HTTP
+   * OpenAPI source with no local overlays).
    * Resolves once the watcher is ready.
    */
   public async watch() {
-    if (this.openapiPath.startsWith("http")) {
+    const watchablePaths = this.openapiPath.startsWith("http")
+      ? [...this.overlays]
+      : [this.openapiPath, ...this.overlays];
+
+    if (watchablePaths.length === 0) {
       return;
     }
 
-    this.watcher = watch(this.openapiPath, CHOKIDAR_OPTIONS).on(
-      "change",
-      () => {
-        void this.generate().then(
-          () => {
-            this.dispatchEvent(new Event("generate"));
-
-            return true;
-          },
-          () => {
-            this.dispatchEvent(new Event("failed"));
-
-            return false;
-          },
-        );
-      },
-    );
+    this.watcher = watch(watchablePaths, CHOKIDAR_OPTIONS).on("change", () => {
+      void this.generate().then(
+        () => {
+          this.dispatchEvent(new Event("generate"));
+
+          return true;
+        },
+        () => {
+          this.dispatchEvent(new Event("failed"));
+
+          return false;
+        },
+      );
+    });
 
     await waitForEvent(this.watcher, "ready");
   }

test/server/code-generator.test.ts

@@ -26,6 +26,18 @@ const OPENAPI = {
   },
 };
 
+const overlayForType = (type: string) =>
+  [
+    "overlay: 1.0.0",
+    "info:",
+    "  title: Example overlay",
+    "  version: 1.0.0",
+    "actions:",
+    "  - target: $.components.schemas.Example",
+    "    update:",
+    `      type: ${type}`,
+  ].join("\n");
+
 describe("a CodeGenerator", () => {
   if (process.platform === "win32") {
     // Not sure why these tests are failing on Windows
@@ -109,6 +121,35 @@ describe("a CodeGenerator", () => {
     });
   });
 
+  it("updates the code when an overlay file changes", async () => {
+    await usingTemporaryFiles(async ({ add, path, read }) => {
+      await add("openapi.json", JSON.stringify(OPENAPI));
+      await add("overlay.yaml", overlayForType("string"));
+
+      const generator = new CodeGenerator(
+        path("./openapi.json"),
+        path("./out"),
+        { routes: true, types: true },
+        "",
+        [path("./overlay.yaml")],
+      );
+
+      await generator.watch();
+
+      await add("overlay.yaml", overlayForType("integer"));
+
+      await waitForEvent(generator, "generate");
+
+      const exampleComponent = await read(
+        "./out/types/components/schemas/Example.ts",
+      );
+
+      await generator.stopWatching();
+
+      expect(exampleComponent).toContain("export type Example = number;\n");
+    });
+  });
+
   it("does not update the code when the spec changes if watch is false", async () => {
     await usingTemporaryFiles(async ({ add, path, read }) => {
       await add("openapi.json", JSON.stringify(OPENAPI));