Export and test `detectedHermesCommand` function from `ReactAppExtension`

Summary:
Another diff to remove code from `ReactAppExtension` to a Util file and test it.

Changelog:
[Internal] [Changed] - Export and test `detectedHermesCommand` function from `ReactAppExtension`

Reviewed By: feedthejim

Differential Revision: D30866510

fbshipit-source-id: 0023a063793d669ee4b2190679ca7fbd01e9a3fc

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

@@ -9,7 +9,6 @@ package com.facebook.react
 
 import com.android.build.gradle.api.BaseVariant
 import java.io.File
-import org.apache.tools.ant.taskdefs.condition.Os
 import org.gradle.api.Project
 
 open class ReactAppExtension(private val project: Project) {
@@ -34,28 +33,4 @@ open class ReactAppExtension(private val project: Project) {
   var hermesFlagsRelease: List<String> = listOf("-O", "-output-source-map")
   var resourcesDir: Map<String, File> = emptyMap()
   var jsBundleDir: Map<String, File> = emptyMap()
-
-  internal val osAwareHermesCommand: String
-    get() = getOSAwareHermesCommand(hermesCommand)
-
-  // Make sure not to inspect the Hermes config unless we need it,
-  // to avoid breaking any JSC-only setups.
-  private fun getOSAwareHermesCommand(hermesCommand: String): String {
-    // If the project specifies a Hermes command, don't second guess it.
-    if (!hermesCommand.contains("%OS-BIN%")) {
-      return hermesCommand
-    }
-
-    // Execution on Windows fails with / as separator
-    return hermesCommand.replace("%OS-BIN%", getHermesOSBin()).replace('/', File.separatorChar)
-  }
-
-  private fun getHermesOSBin(): String {
-    if (Os.isFamily(Os.FAMILY_WINDOWS)) return "win64-bin"
-    if (Os.isFamily(Os.FAMILY_MAC)) return "osx-bin"
-    if (Os.isOs(null, "linux", "amd64", null)) return "linux64-bin"
-    error(
-        "OS not recognized. Please set project.react.hermesCommand " +
-            "to the path of a working Hermes compiler.")
-  }
 }

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

@@ -15,6 +15,7 @@ import com.facebook.react.tasks.BundleJsAndAssetsTask
 import com.facebook.react.tasks.HermesBinaryTask
 import com.facebook.react.utils.detectedCliPath
 import com.facebook.react.utils.detectedEntryFile
+import com.facebook.react.utils.detectedHermesCommand
 import java.io.File
 import org.gradle.api.Project
 import org.gradle.api.tasks.Copy
@@ -94,7 +95,7 @@ internal fun Project.configureReactTasks(variant: BaseVariant, config: ReactAppE
         it.description = "bundle hermes resources for $targetName"
 
         it.reactRoot = config.reactRoot
-        it.hermesCommand = config.osAwareHermesCommand
+        it.hermesCommand = detectedHermesCommand(config)
         it.hermesFlags = if (isRelease) config.hermesFlagsRelease else config.hermesFlagsDebug
         it.jsBundleFile = jsBundleFile
         it.composeSourceMapsCommand = nodeExecutableAndArgs + config.composeSourceMapsPath

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

@@ -9,6 +9,7 @@ package com.facebook.react.utils
 
 import com.facebook.react.ReactAppExtension
 import java.io.File
+import org.apache.tools.ant.taskdefs.condition.Os
 
 /**
  * Computes the entry file for React Native. The Algo follows this order:
@@ -36,6 +37,16 @@ internal fun detectedCliPath(
     detectCliPath(
         projectDir = projectDir, reactRoot = config.reactRoot, preconfuredCliPath = config.cliPath)
 
+/**
+ * Computes the `hermesc` command location. The Algo follows this order:
+ * 1. The path provided by the `hermesCommand` config in the `reactApp` Gradle extension
+ * 2. The file located in `node_modules/hermes-engine/%OS-BIN%/hermesc` where `%OS-BIN%` is
+ * substituted with the correct OS arch.
+ * 3. Fails otherwise
+ */
+internal fun detectedHermesCommand(config: ReactAppExtension): String =
+    detectOSAwareHermesCommand(config.hermesCommand)
+
 private fun detectEntryFile(entryFile: File?, reactRoot: File): File =
     when {
       System.getenv("ENTRY_FILE") != null -> File(System.getenv("ENTRY_FILE"))
@@ -72,3 +83,24 @@ private fun detectCliPath(projectDir: File, reactRoot: File, preconfuredCliPath:
       "Couldn't determine CLI location. " +
           "Please set `project.react.cliPath` to the path of the react-native cli.js")
 }
+
+// Make sure not to inspect the Hermes config unless we need it,
+// to avoid breaking any JSC-only setups.
+private fun detectOSAwareHermesCommand(hermesCommand: String): String {
+  // If the project specifies a Hermes command, don't second guess it.
+  if (!hermesCommand.contains("%OS-BIN%")) {
+    return hermesCommand
+  }
+
+  // Execution on Windows fails with / as separator
+  return hermesCommand.replace("%OS-BIN%", getHermesOSBin()).replace('/', File.separatorChar)
+}
+
+private fun getHermesOSBin(): String {
+  if (Os.isFamily(Os.FAMILY_WINDOWS)) return "win64-bin"
+  if (Os.isFamily(Os.FAMILY_MAC)) return "osx-bin"
+  if (Os.isOs(null, "linux", "amd64", null)) return "linux64-bin"
+  error(
+      "OS not recognized. Please set project.react.hermesCommand " +
+          "to the path of a working Hermes compiler.")
+}

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

@@ -10,9 +10,10 @@ package com.facebook.react.tests
 import com.facebook.react.ReactAppExtension
 import com.facebook.react.utils.detectedCliPath
 import com.facebook.react.utils.detectedEntryFile
+import com.facebook.react.utils.detectedHermesCommand
 import java.io.File
 import org.gradle.testfixtures.ProjectBuilder
-import org.junit.Assert.assertEquals
+import org.junit.Assert.*
 import org.junit.Rule
 import org.junit.Test
 import org.junit.rules.TemporaryFolder
@@ -88,4 +89,26 @@ class PathUtilsTest {
 
     detectedCliPath(project.projectDir, extension)
   }
+
+  @Test
+  fun detectedHermesCommand_withPathFromExtension() {
+    val extension = ReactAppExtension(ProjectBuilder.builder().build())
+    val expected = tempFolder.newFile("hermesc")
+    extension.hermesCommand = expected.toString()
+
+    val actual = detectedHermesCommand(extension)
+
+    assertEquals(expected.toString(), actual)
+  }
+
+  @Test
+  fun detectedHermesCommand_withOSSpecificBin() {
+    val extension = ReactAppExtension(ProjectBuilder.builder().build())
+
+    val actual = detectedHermesCommand(extension)
+
+    assertTrue(actual.startsWith("node_modules/hermes-engine/"))
+    assertTrue(actual.endsWith("hermesc"))
+    assertFalse(actual.contains("%OS-BIN%"))
+  }
 }