Setup a Gradle build inside ReactAndroid/hermes-engine to download Hermes sources

Summary:
This Diff sets up a small Gradle build inside `ReactAndroid/hermes-engine`
The idea is to kickoff a small project where we can download Hermes sources and start a compilation of
the Hermes sources from there.

Specifically the used paths are:

- `/sdk/hermes` for the unzipping
- `/sdk/download/hermes.tar.gz` for the tarball location
- `/sdk/hermes/.hermesversion` for the hermes version.

allow-large-files

Changelog:
[Internal] [Changed] - Setup a Gradle build inside `hermes-engine` to download Hermes sources

Reviewed By: hramos

Differential Revision: D34210236

fbshipit-source-id: 97034f5608dfb3fcd1d74e9851944f7a60e52ea1

.gitignore

@@ -24,6 +24,7 @@ project.xcworkspace
 # Gradle
 /build/
 /packages/react-native-gradle-plugin/build/
+/packages/rn-tester/build
 /packages/rn-tester/android/app/.cxx/
 /packages/rn-tester/android/app/build/
 /packages/rn-tester/android/app/gradle/
@@ -34,6 +35,7 @@ project.xcworkspace
 /ReactAndroid/gradle/
 /ReactAndroid/gradlew
 /ReactAndroid/gradlew.bat
+/ReactAndroid/hermes-engine/build/
 /template/android/app/build/
 /template/android/build/
 
@@ -72,6 +74,7 @@ package-lock.json
 
 # Hermes
 /sdks/hermes
+/sdks/download
 
 # Test generated files
 /ReactAndroid/src/androidTest/assets/AndroidTestBundle.js
@@ -85,8 +88,6 @@ package-lock.json
 
 # ReactCommon subdir shouldn't have Xcode project
 /ReactCommon/**/*.xcodeproj
-/packages/rn-tester/build
-/packages/rn-tester/android/app/build/*
 
 # Libs that shouldn't have Xcode project
 /Libraries/FBLazyVector/**/*.xcodeproj

ReactAndroid/hermes-engine/build.gradle

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+plugins {
+    id("de.undercouch.download")
+}
+
+def customDownloadDir = System.getenv("REACT_NATIVE_DOWNLOADS_DIR")
+def downloadsDir = customDownloadDir ? new File(customDownloadDir) : rootProject.file("sdks/download")
+def hermesDir = rootProject.file("sdks/hermes")
+def hermesVersion = "main"
+def hermesVersionFile = rootProject.file("sdks/.hermesversion")
+if (hermesVersionFile.exists()) {
+    hermesVersion = hermesVersionFile.text
+}
+
+task downloadHermes(type: Download) {
+    src("https://github.com/facebook/hermes/tarball/${hermesVersion}")
+    onlyIfNewer(true)
+    overwrite(false)
+    dest(new File(downloadsDir, "hermes.tar.gz"))
+}
+
+// This task is called by the CI to download all the extrenal source code tarballs.
+task downloadNdkBuildDependencies() {
+    dependsOn(downloadHermes)
+}
+
+task unzipHermes(dependsOn: downloadHermes, type: Copy) {
+    from(tarTree(downloadHermes.dest)) {
+        eachFile { file ->
+            // We flatten the unzip as the tarball contains a `facebook-hermes-<SHA>`
+            // folder at the top level.
+            if (file.relativePath.segments.size() > 1) {
+                file.relativePath = new org.gradle.api.file.RelativePath(!file.isDirectory(), file.relativePath.segments.drop(1))
+            }
+        }
+    }
+    into(hermesDir)
+}

settings.gradle.kts

@@ -15,6 +15,7 @@ pluginManagement {
 
 include(
     ":ReactAndroid",
+    ":ReactAndroid:hermes-engine",
     ":packages:react-native-codegen:android",
     ":packages:rn-tester:android:app"
 )
@@ -32,4 +33,4 @@ plugins {
 // you can configure your custom Gradle Enterprise instance
 if (File("./gradle/gradle-enterprise.gradle.kts").exists()) {
     apply(from = "./gradle/gradle-enterprise.gradle.kts")
-}
+}