vendor-hermes: export public hermes_napi_* entry points

The clean Hermes build at the pinned SHA does NOT export
hermes_napi_create_env (and the other hermes_napi_* entry points): Hermes
compiles every target with a global -fvisibility=hidden, and because those
entry points are C++ symbols taking hermes_napi_host*, a function's
visibility is clamped by its parameter types' hidden visibility — so they
stay out of the framework's dynamic export table even though they carry
NAPI_EXTERN. Last session's env creation only linked because the pod's
Hermes binary was hand-patched; a from-scratch build fails at the app link
with "Undefined symbol: hermes_napi_create_env".

vendor-hermes now appends `-fvisibility=default` to the hermesNapi_obj
CMake target (idempotently, after cloning), overriding the earlier global
flag for that target only. Verified via nm that the entry points now export
(napi/node_api runtime symbols unaffected) and the iOS allTests suite is
green (14 passing) from a clean pod build — no binary hand-patching.

Also ignore **/build-tests/** in ESLint (CMake writes compiler_depend.ts
dependency files there that aren't real TypeScript).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kraenhansen

eslint.config.js

@@ -10,6 +10,7 @@ export default tseslint.config(
   globalIgnores([
     "**/dist/**",
     "**/build/**",
+    "**/build-tests/**",
     "apps/test-app/ios/**",
     "apps/macos-test-app/**",
     "packages/host/hermes/**",

packages/host/src/node/cli/hermes.ts

@@ -28,6 +28,31 @@ const platformOption = new Option(
   "The React Native package to vendor Hermes into",
 ).default("react-native");
 
+// Hermes builds every target with a global `-fvisibility=hidden`. The public
+// `hermes_napi_*` entry points (e.g. `hermes_napi_create_env`) are C++ symbols
+// that take a `hermes_napi_host*`, so under that flag a C++ function's
+// visibility is clamped by its parameter types' hidden visibility — keeping the
+// entry points out of the shared framework's export table even though they
+// carry NAPI_EXTERN. We reach `hermes_napi_create_env` from the host module, so
+// it must be exported. Appending `-fvisibility=default` to the napi object
+// target overrides the earlier global flag for that target only, exporting the
+// entry points (and their parameter types) without touching the rest of Hermes.
+const HERMES_NAPI_CMAKELISTS = "API/napi/CMakeLists.txt";
+const HERMES_NAPI_VISIBILITY_PATCH =
+  "target_compile_options(hermesNapi_obj PRIVATE -fvisibility=default)";
+
+async function patchHermesNapiVisibility(hermesPath: string) {
+  const cmakeListsPath = path.join(hermesPath, HERMES_NAPI_CMAKELISTS);
+  const contents = await fs.promises.readFile(cmakeListsPath, "utf8");
+  if (contents.includes(HERMES_NAPI_VISIBILITY_PATCH)) {
+    return;
+  }
+  await fs.promises.writeFile(
+    cmakeListsPath,
+    `${contents.trimEnd()}\n\n# Patched by react-native-node-api: export the public hermes_napi_*\n# entry points from the shared framework (see vendor-hermes).\n${HERMES_NAPI_VISIBILITY_PATCH}\n`,
+  );
+}
+
 export const command = new Command("vendor-hermes")
   .argument("[from]", "Path to a file inside the app package", process.cwd())
   .option("--silent", "Don't print anything except the final path", false)
@@ -115,6 +140,9 @@ export const command = new Command("vendor-hermes")
           });
         }
       }
+      // Applied unconditionally (idempotent) so an existing checkout from
+      // before this patch also gets fixed.
+      await patchHermesNapiVisibility(hermesPath);
       console.log(hermesPath);
     }),
   );