Ensure REACT_NATIVE_OVERRIDE_HERMES_DIR is set

Author: kraenhansen

packages/host/android/build.gradle

@@ -134,6 +134,22 @@ dependencies {
   implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
 }
 
+task checkHermesOverride {
+    doFirst {
+        if (!System.getenv("REACT_NATIVE_OVERRIDE_HERMES_DIR")) {
+            throw new GradleException([
+                "React Native Node-API needs a custom version of Hermes with Node-API enabled.",
+                "Run the following in your terminal, to clone Hermes and instruct React Native to use it:",
+                "",
+                "export REACT_NATIVE_OVERRIDE_HERMES_DIR=`npx react-native-node-api vendor-hermes --silent --force`",
+                "",
+                "And follow this guide to build React Native from source:",
+                "https://reactnative.dev/contributing/how-to-build-from-source#update-your-project-to-build-from-source"
+            ].join('\n'))
+        }
+    }
+}
+
 // Custom task to fetch jniLibs paths via CLI
 task linkNodeApiModules {
   doLast {
@@ -150,5 +166,5 @@ task linkNodeApiModules {
   }
 }
 
-preBuild.dependsOn linkNodeApiModules
+preBuild.dependsOn checkHermesOverride, linkNodeApiModules
 

packages/host/src/node/gradle.test.ts

@@ -0,0 +1,45 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import cp from "node:child_process";
+import path from "node:path";
+
+const PACKAGE_ROOT = path.join(__dirname, "../..");
+const MONOREPO_ROOT = path.join(PACKAGE_ROOT, "../..");
+const TEST_APP_ANDROID_PATH = path.join(MONOREPO_ROOT, "apps/test-app/android");
+
+describe("Gradle tasks", () => {
+  describe("checkHermesOverride task", () => {
+    it("should fail if REACT_NATIVE_OVERRIDE_HERMES_DIR is not set", () => {
+      const { status, stdout, stderr } = cp.spawnSync(
+        "sh",
+        ["gradlew", "react-native-node-api:checkHermesOverride"],
+        {
+          cwd: TEST_APP_ANDROID_PATH,
+          env: {
+            ...process.env,
+            REACT_NATIVE_OVERRIDE_HERMES_DIR: undefined,
+          },
+          encoding: "utf-8",
+        },
+      );
+
+      assert.notEqual(status, 0, `Expected failure: ${stdout} ${stderr}`);
+      assert.match(
+        stderr,
+        /React Native Node-API needs a custom version of Hermes with Node-API enabled/,
+      );
+      assert.match(
+        stderr,
+        /Run the following in your terminal, to clone Hermes and instruct React Native to use it/,
+      );
+      assert.match(
+        stderr,
+        /export REACT_NATIVE_OVERRIDE_HERMES_DIR=`npx react-native-node-api vendor-hermes --silent --force`/,
+      );
+      assert.match(
+        stderr,
+        /And follow this guide to build React Native from source/,
+      );
+    });
+  });
+});