fix(spm): complete SwiftPM Release fixes surfaced by the build matrix

Follow-up to the prior Release-support commit — two gaps the ios-build-matrix
Release run exposed that the prior commit missed.

- (A, completion) The codegen ReactCodegen / ReactAppDependencyProvider targets
  were NOT getting NDEBUG. That is where the app's codegen'd Fabric C++ lives
  (RNTMyNativeViewProps), so rn-tester still failed to link with an undefined
  "vtable for DebugStringConvertible". Add the DEBUG/NDEBUG config defines to
  scripts/codegen/templates/Package.swift.spm-template (the SPM codegen manifest
  installed by spm sync). Verified: rn-tester SPM Release now BUILD SUCCEEDED.
- (B, fix) HERMES_CLI_PATH must be ABSOLUTE, not `$(REACT_NATIVE_PATH)/../…`.
  node_modules/react-native is commonly a SYMLINK (monorepo default + many real
  apps); a `..` after it resolves — kernel-side — to the symlink TARGET's parent
  (packages/), so the relative path pointed at a non-existent
  packages/hermes-compiler and Release JS bundling failed with "No such file".
  resolveHermesCliPathSetting now returns the require.resolve'd absolute hermesc
  path (regenerated per `spm add`; matches how the hermes-engine pod sets it).
  Verified: HelloWorld SPM Release now BUILD SUCCEEDED.

Matrix: helloworld + rn-tester SPM Release both PASS (newapp pending a Verdaccio
re-publish of these scripts).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: chrfalch

packages/react-native/scripts/codegen/templates/Package.swift.spm-template

@@ -53,7 +53,17 @@ let package = Package(
             exclude: ["ReactCodegen.podspec"],
             publicHeadersPath: ".",
             cSettings: [.headerSearchPath("headers")],
-            cxxSettings: [.headerSearchPath("headers")],
+            // DEBUG/NDEBUG match the prebuilt React.framework's config-gated C++
+            // ABI: NDEBUG (Release) strips DebugStringConvertible's vtable and
+            // shifts the ShadowNode layout that codegen'd Props inherit, so this
+            // target must compile with the same NDEBUG state or the Release link
+            // fails (undefined "vtable for DebugStringConvertible"). Mirrors
+            // packages/react-native/Package.swift.
+            cxxSettings: [
+                .headerSearchPath("headers"),
+                .define("DEBUG", .when(configuration: .debug)),
+                .define("NDEBUG", .when(configuration: .release)),
+            ],
             linkerSettings: [
                 .linkedFramework("Foundation")
             ]
@@ -65,7 +75,13 @@ let package = Package(
             exclude: ["ReactAppDependencyProvider.podspec"],
             publicHeadersPath: ".",
             cSettings: [.headerSearchPath(".."), .headerSearchPath("headers")],
-            cxxSettings: [.headerSearchPath(".."), .headerSearchPath("headers")],
+            cxxSettings: [
+                .headerSearchPath(".."),
+                .headerSearchPath("headers"),
+                // Match the prebuilt React.framework NDEBUG-gated C++ ABI (see above).
+                .define("DEBUG", .when(configuration: .debug)),
+                .define("NDEBUG", .when(configuration: .release)),
+            ],
             linkerSettings: [
                 .linkedFramework("Foundation")
             ]

packages/react-native/scripts/spm/__tests__/inject-spm-xcodeproj-test.js

@@ -31,7 +31,12 @@ const PODS = PLAIN.replace(
 
 const RN_PATH = '../node_modules/react-native';
 
-function inject(text, remote = null) {
+// Absolute, mirroring resolveHermesCliPathSetting (a `..`-relative path through
+// a symlinked react-native would resolve to the wrong dir at build time).
+const TEST_HERMES_CLI_PATH =
+  '/abs/node_modules/hermes-compiler/hermesc/osx-bin/hermesc';
+
+function inject(text, remote = null, hermesCliPath = TEST_HERMES_CLI_PATH) {
   const plan = planInjection(text, {});
   expect(plan.ok).toBe(true);
   return injectSpmIntoPbxproj(
@@ -44,6 +49,7 @@ function inject(text, remote = null) {
     },
     RN_PATH,
     remote,
+    hermesCliPath,
   );
 }
 
@@ -150,9 +156,12 @@ describe('injectSpmIntoPbxproj — Tier 2 (build settings + phase)', () => {
     // HERMES_CLI_PATH points react-native-xcode.sh at the hermes-compiler npm
     // package (no hermes-engine pod under SPM), injected into both configs.
     expect(text.match(/HERMES_CLI_PATH = /g)).toHaveLength(2);
-    expect(text).toContain(
-      '$(REACT_NATIVE_PATH)/../hermes-compiler/hermesc/osx-bin/hermesc',
-    );
+    expect(text).toContain(TEST_HERMES_CLI_PATH);
+  });
+
+  it('omits HERMES_CLI_PATH when hermesc could not be resolved', () => {
+    const {text} = inject(PLAIN, null, null);
+    expect(text).not.toContain('HERMES_CLI_PATH');
   });
 
   it('prepends the Sync SPM Autolinking build phase', () => {

packages/react-native/scripts/spm/generate-spm-xcodeproj.js

@@ -759,6 +759,7 @@ function injectSpmIntoPbxproj(
   plan /*: {rootUuid: string, targetUuid: string, configUuids: Array<string>, frameworksPhaseUuid: string} */,
   reactNativePath /*: string */,
   remote /*: ?RemoteCfg */,
+  hermesCliPath /*: ?string */ = null,
 ) /*: {text: string, injectedUuids: Array<string>, createdArrayFields: Array<{container: 'project' | 'target', key: string}>, buildSettingChanges: Array<BuildSettingChange>} */ {
   let text = input;
   const mkUuid = (section /*: string */, id /*: string */) =>
@@ -853,7 +854,12 @@ function injectSpmIntoPbxproj(
   // 5. React build settings into every build config (Debug + Release).
   const buildSettingChanges /*: Array<BuildSettingChange> */ = [];
   for (const configUuid of plan.configUuids) {
-    const merged = mergeReactBuildSettings(text, configUuid, reactNativePath);
+    const merged = mergeReactBuildSettings(
+      text,
+      configUuid,
+      reactNativePath,
+      hermesCliPath,
+    );
     text = merged.text;
     buildSettingChanges.push(merged.change);
   }
@@ -904,10 +910,46 @@ function findApplicationTargetByUuid(
  * a value the user already had (key insight: ensureScalarField/
  * addArrayStringValues are no-ops / dedupe when a value is already present).
  */
+/**
+ * Resolves the host `hermesc` from the `hermes-compiler` npm package and returns
+ * its ABSOLUTE path as the HERMES_CLI_PATH value, or null when it can't be found
+ * (e.g. USE_HERMES=false apps without the package). require.resolve (anchored at
+ * reactNativeRoot) follows Node's lookup, so a hoisted monorepo layout — where
+ * hermes-compiler sits in the workspace-root node_modules, NOT next to
+ * react-native — resolves correctly.
+ *
+ * The value is intentionally ABSOLUTE, not `$(REACT_NATIVE_PATH)/../...`: when
+ * react-native is a symlink (the monorepo default, and common in real apps), a
+ * `..` after it resolves — kernel-side — to the symlink TARGET's parent, not the
+ * node_modules dir, so the relative form points at a non-existent
+ * `<rn-target>/../hermes-compiler`. An absolute path sidesteps that entirely
+ * (and matches how the CocoaPods hermes-engine pod sets HERMES_CLI_PATH). It is
+ * regenerated on every `spm add`, so machine-specificity is a non-issue.
+ */
+function resolveHermesCliPathSetting(
+  reactNativeRoot /*: string */,
+) /*: ?string */ {
+  try {
+    const pkg = require.resolve('hermes-compiler/package.json', {
+      paths: [reactNativeRoot],
+    });
+    const hermesc = path.join(
+      path.dirname(pkg),
+      'hermesc',
+      'osx-bin',
+      'hermesc',
+    );
+    return fs.existsSync(hermesc) ? hermesc : null;
+  } catch {
+    return null;
+  }
+}
+
 function mergeReactBuildSettings(
   input /*: string */,
   configUuid /*: string */,
   reactNativePath /*: string */,
+  hermesCliPath /*: ?string */ = null,
 ) /*: {text: string, change: BuildSettingChange} */ {
   let text = input;
   const scalars = [
@@ -917,14 +959,13 @@ function mergeReactBuildSettings(
     // fallback ($PODS_ROOT/hermes-engine/destroot/bin/hermesc) resolves to a
     // non-existent "/hermes-engine/..." and the Release JS→Hermes bundling
     // fails. Point HERMES_CLI_PATH at the hermes-compiler npm package's host
-    // hermesc (sibling of react-native in node_modules). react-native-xcode.sh
-    // honors an already-set HERMES_CLI_PATH before its pod fallback; the
-    // ensureScalarField below leaves any user-provided value untouched.
-    {
-      key: 'HERMES_CLI_PATH',
-      value:
-        '"$(REACT_NATIVE_PATH)/../hermes-compiler/hermesc/osx-bin/hermesc"',
-    },
+    // hermesc (an ABSOLUTE path resolved by the caller — see
+    // resolveHermesCliPathSetting). react-native-xcode.sh honors an already-set
+    // HERMES_CLI_PATH before its pod fallback; ensureScalarField leaves any
+    // user-provided value untouched.
+    ...(hermesCliPath != null
+      ? [{key: 'HERMES_CLI_PATH', value: quoteIfNeeded(hermesCliPath)}]
+      : []),
   ];
   // Re-locate the buildSettings dict before each edit (offsets shift).
   const dict = () => {
@@ -1161,6 +1202,7 @@ function injectSpmIntoExistingXcodeproj(
   }
   const reactNativePath = path.relative(appRoot, reactNativeRoot);
   const remote = remotePackageConfig(appRoot);
+  const hermesCliPath = resolveHermesCliPathSetting(reactNativeRoot);
   const {text, injectedUuids, createdArrayFields, buildSettingChanges} =
     injectSpmIntoPbxproj(
       original,
@@ -1172,6 +1214,7 @@ function injectSpmIntoExistingXcodeproj(
       },
       reactNativePath,
       remote,
+      hermesCliPath,
     );
 
   const changed = writeIfChanged(pbxprojPath, text);