Stop the host Hermes compiler build from targeting visionOS (#443)

* Dump the CMake configure log when the Hermes build fails

CMake reports a failed feature check as a bare "not found", with the
compiler's actual complaint only in its configure log. The host hermesc
configure is failing on the macOS runner with checks that succeed
everywhere else, so surface that log rather than guess at it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UkNbgdyuKgHaFwT27RahGH

* Stop the host Hermes compiler build from targeting visionOS

Every command got all three deployment targets build-apple-framework.sh
can ask for, including the host compiler build. XROS_DEPLOYMENT_TARGET is
also a clang driver variable, so clang targeted visionOS against the macOS
sysroot:

  clang: warning: using sysroot for 'MacOSX' but targeting 'XR'
  error: 'pthread_mutexattr_init' is unavailable: not available on visionOS

Every API marked unavailable on visionOS then failed to compile, which is
why unistd.h (which reaches _fd_def.h through sys/select.h) came back "not
found" while sys/stat.h did not, and why the configure died on CheckAtomic.

Each platform build now gets only the deployment target it needs, and the
host compiler build gets none.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UkNbgdyuKgHaFwT27RahGH

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: kraenhansen

.changeset/prebuilt-hermes-visionos-env.md

@@ -0,0 +1,13 @@
+---
+"react-native-node-api": patch
+---
+
+Fix `prebuilt-hermes` failing to configure the host Hermes compiler with "Host
+compiler appears to require libatomic, but cannot find it". It exported all
+three deployment targets Hermes' `build-apple-framework.sh` can ask for to every
+command it ran, including the host compiler build. `XROS_DEPLOYMENT_TARGET` is
+also a clang driver variable, so clang targeted visionOS against the macOS
+sysroot, and every API marked unavailable there — `pthread_mutexattr_init`, the
+`fd_set` helpers reached through `unistd.h` — failed to compile. Each platform
+build now gets only the deployment target it needs, and the host compiler build
+gets none.

.github/workflows/hermes-prebuilt.yml

@@ -67,6 +67,37 @@ jobs:
         run: |
           path=$(pnpm exec react-native-node-api prebuilt-hermes --no-download)
           echo "path=$path" >> "$GITHUB_OUTPUT"
+      # CMake reports a failed feature check as a bare "not found", with the
+      # compiler's actual complaint only in its configure log. Surface that log
+      # here so a failure is diagnosable without another round trip.
+      - name: Dump CMake configure log
+        if: failure()
+        run: |
+          log=$(find "$PWD" -name CMakeConfigureLog.yaml -path '*build_host_hermesc*' | head -1)
+          if [ -z "$log" ]; then
+            echo "No CMakeConfigureLog.yaml found"
+            find "$PWD" -name 'CMakeError.log' -path '*build_host_hermesc*' -exec cat {} \;
+            exit 0
+          fi
+          echo "::group::Environment seen by CMake"
+          env | sort
+          xcode-select --print-path
+          xcrun --show-sdk-path || true
+          echo "::endgroup::"
+          echo "::group::unistd.h check"
+          grep -n -B 5 -A 45 'unistd\.h' "$log" | head -150
+          echo "::endgroup::"
+          echo "::group::atomics check"
+          grep -n -B 5 -A 60 'HAVE_CXX_ATOMICS_WITHOUT_LIB' "$log" | head -180
+          echo "::endgroup::"
+          cp "$log" "$RUNNER_TEMP/CMakeConfigureLog.yaml"
+      - name: Upload CMake configure log
+        if: failure()
+        uses: actions/upload-artifact@v7
+        with:
+          name: hermesc-cmake-configure-log
+          path: ${{ runner.temp }}/CMakeConfigureLog.yaml
+          if-no-files-found: ignore
       # --latest=false keeps these out of the "latest release" slot, which
       # belongs to the package releases changesets publishes.
       - name: Publish as a release asset

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

@@ -27,13 +27,25 @@ const RELEASES_URL =
 
 export const DEFAULT_PLATFORMS = ["iphoneos", "iphonesimulator"];
 
-// Passed to Hermes' build-apple-framework.sh, which errors out rather than
-// assume one. These match React Native's own podspec declarations.
-const DEPLOYMENT_TARGETS = {
-  IOS_DEPLOYMENT_TARGET: "15.1",
-  MAC_DEPLOYMENT_TARGET: "10.15",
-  XROS_DEPLOYMENT_TARGET: "1.0",
-};
+/**
+ * The deployment target build-apple-framework.sh reads for a platform — it
+ * errors out rather than assume one. These match React Native's own podspec
+ * declarations.
+ *
+ * Only the variable that platform needs is passed. XROS_DEPLOYMENT_TARGET is
+ * also a clang driver variable, so leaking it into a build that isn't for
+ * visionOS makes clang target visionOS against whatever sysroot it was given —
+ * and every API marked unavailable there then fails to compile.
+ */
+function getDeploymentTarget(platform: string): Record<string, string> {
+  if (platform === "macosx") {
+    return { MAC_DEPLOYMENT_TARGET: "10.15" };
+  } else if (platform === "xros" || platform === "xrsimulator") {
+    return { XROS_DEPLOYMENT_TARGET: "1.0" };
+  } else {
+    return { IOS_DEPLOYMENT_TARGET: "15.1" };
+  }
+}
 
 export const BUILD_TYPES = ["debug", "release"] as const;
 export type BuildType = (typeof BUILD_TYPES)[number];
@@ -162,15 +174,19 @@ async function buildArchive({
   // vendored copy: the framework and the app linking it share jsi::Runtime.
   const jsiPath = path.join(reactNativePath, "ReactCommon", "jsi");
 
-  const run = (command: string, args: string[]) =>
+  const run = (
+    command: string,
+    args: string[],
+    extraEnv: Record<string, string> = {},
+  ) =>
     spawn(command, args, {
       cwd: hermesPath,
       outputMode: "inherit",
       // Keeps the build log off stdout, which callers parse for the final path.
       stdout: process.stderr,
       env: {
-        ...DEPLOYMENT_TARGETS,
         ...process.env,
+        ...extraEnv,
         JSI_PATH: jsiPath,
         BUILD_TYPE: buildType === "debug" ? "Debug" : "Release",
         HERMES_OVERRIDE_HERMESC_PATH: importHostCompilersPath,
@@ -202,7 +218,11 @@ async function buildArchive({
   }
 
   for (const platform of platforms) {
-    await run("./utils/build-apple-framework.sh", [platform]);
+    await run(
+      "./utils/build-apple-framework.sh",
+      [platform],
+      getDeploymentTarget(platform),
+    );
   }
 
   const frameworksPath = path.join(