Fix Hermes compiler detection for monorepos

packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/tasks/BundleHermesCTask.kt

@@ -94,7 +94,12 @@ abstract class BundleHermesCTask : DefaultTask() {
     runCommand(bundleCommand)
 
     if (hermesEnabled.get()) {
-      val detectedHermesCommand = detectOSAwareHermesCommand(root.get().asFile, hermesCommand.get())
+      val detectedHermesCommand =
+          detectOSAwareHermesCommand(
+              root.get().asFile,
+              hermesCommand.get(),
+              reactNativeDir.get().asFile,
+          )
       val bytecodeFile = File("${bundleFile}.hbc")
       val outputSourceMap = resolveOutputSourceMap(bundleAssetFilename)
       val compilerSourceMap = resolveCompilerSourceMap(bundleAssetFilename)

packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/utils/PathUtils.kt

@@ -57,7 +57,11 @@ internal fun detectedCliFile(config: ReactExtension): File =
  * 4. Fails otherwise
  */
 internal fun detectedHermesCommand(config: ReactExtension): String =
-    detectOSAwareHermesCommand(config.root.get().asFile, config.hermesCommand.get())
+    detectOSAwareHermesCommand(
+        config.root.get().asFile,
+        config.hermesCommand.get(),
+        config.reactNativeDir.get().asFile,
+    )
 
 private fun detectEntryFile(
     entryFile: File?,
@@ -120,16 +124,20 @@ private fun detectCliFile(
 /**
  * Computes the `hermesc` command location. The Algo follows this order:
  * 1. The path provided by the `hermesCommand` config in the `react` Gradle extension
- * 2. The file located in `node_modules/react-native/sdks/hermes/build/bin/hermesc`. This will be
+ * 2. The file located in
+ *    `node_modules/react-native/ReactAndroid/hermes-engine/build/hermes/bin/hermesc`. This will be
  *    used if the user is building Hermes from source.
- * 3. The file located in `node_modules/hermes-compiler/%OS-BIN%/hermesc` where `%OS-BIN%` is
- *    substituted with the correct OS arch. This is used when Hermes V1 is consumed as a prebuilt
+ * 3. The built from source hermesc located under the configured `reactNativeDir`.
+ * 4. The file located in `node_modules/hermes-compiler/hermesc/%OS-BIN%/hermesc` where `%OS-BIN%` is
+ *    substituted with the correct OS arch. This is used when Hermes is consumed as a prebuilt
  *    package via the `hermes-compiler` npm package.
- * 4. Fails otherwise
+ * 5. The prebuilt `hermes-compiler` package located next to the configured `reactNativeDir`.
+ * 6. Fails otherwise
  */
 internal fun detectOSAwareHermesCommand(
     projectRoot: File,
     hermesCommand: String,
+    reactNativeDir: File? = null,
 ): String { // 1. If the project specifies a Hermes command, don't second guess it.
   if (hermesCommand.isNotBlank()) {
     val osSpecificHermesCommand =
@@ -144,31 +152,52 @@ internal fun detectOSAwareHermesCommand(
   }
 
   // 2. If the project is building hermes-engine from source, use hermesc from there
-  val builtHermesc =
-      getBuiltHermescFile(projectRoot, System.getenv("REACT_NATIVE_OVERRIDE_HERMES_DIR"))
-  if (builtHermesc.exists()) {
-    return builtHermesc.cliPath(projectRoot)
-  }
+  val builtHermescCandidates =
+      listOfNotNull(
+          getBuiltHermescFile(projectRoot, System.getenv("REACT_NATIVE_OVERRIDE_HERMES_DIR")),
+          reactNativeDir?.let { getBuiltHermescFileFromReactNativeDir(it) },
+      )
+  builtHermescCandidates.firstOrNull { it.exists() }?.let { return it.cliPath(projectRoot) }
+
+  val prebuiltHermesCandidates = getHermesCompilerCandidates(projectRoot, reactNativeDir)
+  prebuiltHermesCandidates.firstOrNull { it.exists() }?.let { return it.cliPath(projectRoot) }
+
+  error(
+      buildString {
+        appendLine("Couldn't determine Hermesc location.")
+        appendLine("Checked:")
+        (builtHermescCandidates + prebuiltHermesCandidates).forEach { appendLine("- ${it.path}") }
+        append(
+            "Please set `react.hermesCommand` to the path of the hermesc binary file, " +
+                "or make sure the `hermes-compiler` package is installed and resolvable from " +
+                "your project root or configured `reactNativeDir`."
+        )
+      }
+  )
+}
 
-  // 3. Use hermes-compiler from npm
+private fun getHermesCompilerCandidates(projectRoot: File, reactNativeDir: File?): List<File> {
   val prebuiltHermesPath =
       HERMES_COMPILER_NPM_DIR.plus(getHermesCBin())
           .replace("%OS-BIN%", getHermesOSBin())
           // Execution on Windows fails with / as separator
           .replace('/', File.separatorChar)
 
-  val prebuiltHermes = File(projectRoot, prebuiltHermesPath)
-  if (prebuiltHermes.exists()) {
-    return prebuiltHermes.cliPath(projectRoot)
-  }
-
-  error(
-      "Couldn't determine Hermesc location. " +
-          "Please set `react.hermesCommand` to the path of the hermesc binary file. " +
-          "node_modules/react-native/sdks/hermesc/%OS-BIN%/hermesc"
-  )
+  return listOfNotNull(
+          File(projectRoot, prebuiltHermesPath),
+          reactNativeDir?.parentFile?.let { nodeModulesDir ->
+            File(nodeModulesDir, prebuiltHermesPath.removePrefix("node_modules${File.separator}"))
+          },
+      )
+      .distinctBy { it.absolutePath }
 }
 
+private fun getBuiltHermescFileFromReactNativeDir(reactNativeDir: File): File =
+    File(
+        reactNativeDir,
+        "ReactAndroid/hermes-engine/build/hermes/bin/${getHermesCBin()}",
+    )
+
 /**
  * Gets the location where Hermesc should be. If nothing is specified, built hermesc is assumed to
  * be inside [HERMESC_BUILT_FROM_SOURCE_DIR]. Otherwise user can specify an override with

packages/gradle-plugin/react-native-gradle-plugin/src/test/kotlin/com/facebook/react/utils/PathUtilsTest.kt

@@ -14,6 +14,7 @@ import com.facebook.react.tests.OsRule
 import com.facebook.react.tests.WithOs
 import java.io.File
 import org.assertj.core.api.Assertions.assertThat
+import org.assertj.core.api.Assertions.assertThatThrownBy
 import org.gradle.process.ProcessExecutionException
 import org.gradle.testfixtures.ProjectBuilder
 import org.junit.Assume.assumeTrue
@@ -163,12 +164,68 @@ class PathUtilsTest {
     assertThat(detectOSAwareHermesCommand(tempFolder.root, "")).isEqualTo(expected.toString())
   }
 
+  @Test
+  @WithOs(OS.MAC)
+  fun detectOSAwareHermesCommand_withHoistedHermescFromNPM() {
+    val projectRoot = tempFolder.newFolder("apps", "mobile")
+    val reactNativeDir = tempFolder.newFolder("node_modules", "react-native")
+    tempFolder.newFolder("node_modules/hermes-compiler/hermesc/osx-bin/")
+    val expected = tempFolder.newFile("node_modules/hermes-compiler/hermesc/osx-bin/hermesc")
+
+    assertThat(detectOSAwareHermesCommand(projectRoot, "", reactNativeDir))
+        .isEqualTo(expected.toString())
+  }
+
+  @Test
+  @WithOs(OS.MAC)
+  fun detectOSAwareHermesCommand_withLocalAndHoistedHermescFromNPM_prefersLocal() {
+    val projectRoot = tempFolder.newFolder("apps", "mobile")
+    val reactNativeDir = tempFolder.newFolder("node_modules", "react-native")
+    File(projectRoot, "node_modules/hermes-compiler/hermesc/osx-bin/").mkdirs()
+    val expected = File(projectRoot, "node_modules/hermes-compiler/hermesc/osx-bin/hermesc")
+    expected.createNewFile()
+    tempFolder.newFolder("node_modules/hermes-compiler/hermesc/osx-bin/")
+    tempFolder.newFile("node_modules/hermes-compiler/hermesc/osx-bin/hermesc")
+
+    assertThat(detectOSAwareHermesCommand(projectRoot, "", reactNativeDir))
+        .isEqualTo(expected.toString())
+  }
+
+  @Test
+  fun detectedHermesCommand_usesConfiguredReactNativeDirForHoistedHermescFromNPM() {
+    val project = ProjectBuilder.builder().build()
+    val extension = TestReactExtension(project)
+    val projectRoot = tempFolder.newFolder("apps", "mobile")
+    val reactNativeDir = tempFolder.newFolder("node_modules", "react-native")
+    extension.root.set(projectRoot)
+    extension.reactNativeDir.set(reactNativeDir)
+    tempFolder.newFolder("node_modules/hermes-compiler/hermesc/${getHermesOSBin()}/")
+    val expected = tempFolder.newFile("node_modules/hermes-compiler/hermesc/${getHermesOSBin()}/hermesc")
+
+    assertThat(detectedHermesCommand(extension)).isEqualTo(expected.toString())
+  }
+
   @Test(expected = IllegalStateException::class)
   @WithOs(OS.MAC)
   fun detectOSAwareHermesCommand_failsIfNotFound() {
     detectOSAwareHermesCommand(tempFolder.root, "")
   }
 
+  @Test
+  @WithOs(OS.MAC)
+  fun detectOSAwareHermesCommand_whenHermescNotFound_reportsCheckedLocations() {
+    val projectRoot = tempFolder.newFolder("apps", "mobile")
+    val reactNativeDir = tempFolder.newFolder("node_modules", "react-native")
+
+    assertThatThrownBy { detectOSAwareHermesCommand(projectRoot, "", reactNativeDir) }
+        .isInstanceOf(IllegalStateException::class.java)
+        .hasMessageContaining("Couldn't determine Hermesc location.")
+        .hasMessageContaining("Checked:")
+        .hasMessageContaining("node_modules/hermes-compiler/hermesc/osx-bin/hermesc")
+        .hasMessageContaining("configured `reactNativeDir`")
+        .hasMessageNotContaining("node_modules/react-native/sdks/hermesc")
+  }
+
   @Test
   @WithOs(OS.MAC)
   fun detectOSAwareHermesCommand_withProvidedCommand_takesPrecedence() {