examples: bazel run that boots a hermetic emulator (demo delta)

examples/cross_compilation/android_app/BUILD.bazel

@@ -11,11 +11,35 @@ load("@bazel_skylib//rules:build_test.bzl", "build_test")
 load("@rules_android//rules:rules.bzl", "android_binary")
 load("@rules_cc//cc:defs.bzl", "cc_library")
 load("@rules_kotlin//kotlin:android.bzl", "kt_android_library")
+load("@rules_shell//shell:sh_binary.bzl", "sh_binary")
 load("//swift:swift.bzl", "swift_binary", "swift_library")
 load("//swift/toolchains:android_runtime_lib.bzl", "select_android_runtime_lib")
 
 package(default_visibility = ["//visibility:public"])
 
+# `bazel run //examples/cross_compilation/android_app:run` installs the APK on a
+# connected device/emulator and launches it, booting a hermetic emulator first
+# if nothing is connected (downloaded emulator + system image; adb from
+# @androidsdk). macOS/arm64 only — see emulator.bzl.
+sh_binary(
+    name = "run",
+    srcs = ["run.sh"],
+    args = [
+        "$(rlocationpath :app.apk)",
+        "$(rlocationpath @androidsdk//:adb)",
+        "$(rlocationpath @android_emulator//:emulator/emulator)",
+        "$(rlocationpath @android_system_image//:system.img)",
+    ],
+    data = [
+        ":app.apk",
+        "@android_emulator//:all",
+        "@android_emulator//:emulator/emulator",
+        "@android_system_image//:all",
+        "@android_system_image//:system.img",
+        "@androidsdk//:adb",
+    ],
+)
+
 android_binary(
     name = "app",
     manifest = "AndroidManifest.xml",

examples/cross_compilation/android_app/README.md

@@ -22,6 +22,17 @@ adb install -r bazel-bin/examples/cross_compilation/android_app/app.apk
 adb shell am start -n com.example.swiftjni/.MainActivity
 ```
 
+Or, with nothing preinstalled (no Android Studio, no device), let Bazel boot a
+hermetic emulator, install, and launch — macOS/arm64:
+
+```sh
+bazel run //examples/cross_compilation/android_app:run
+```
+
+This downloads the emulator + an AOSP system image (see `emulator.bzl`) and uses
+adb from `@androidsdk`; if a device/emulator is already connected it just installs
+and launches on that.
+
 The screen shows **“Hello from Swift, Android!”** — computed by the `Greeter`
 `swift_library`, returned through the `@_cdecl` JNI entry point in
 `libSwiftJNI.so`, and displayed by Kotlin. (`//.bazelrc` sets

examples/cross_compilation/android_app/android.MODULE.bazel

@@ -66,3 +66,12 @@ register_toolchains(
     "@androidsdk//:all",
     dev_dependency = True,
 )
+
+# A hermetic emulator + system image so `bazel run …:run` can launch the example
+# with nothing preinstalled (adb comes from @androidsdk).
+emulator = use_extension(
+    "//examples/cross_compilation/android_app:emulator.bzl",
+    "emulator",
+    dev_dependency = True,
+)
+use_repo(emulator, "android_emulator", "android_system_image")

examples/cross_compilation/android_app/emulator.bzl

@@ -0,0 +1,45 @@
+"""A dev module extension that downloads a hermetic Android emulator and a
+system image, so `bazel run //examples/cross_compilation/android_app:run` can
+boot an emulator and launch the example with nothing preinstalled.
+
+macOS/arm64 only, to keep this illustrative delta small (it's the platform the
+example's CI runs on). adb comes from `@androidsdk`; only the emulator and the
+system image — which `@androidsdk` does not provide — are downloaded here.
+"""
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+_EMULATOR_BUILD = """\
+package(default_visibility = ["//visibility:public"])
+
+exports_files(["emulator/emulator"])
+
+filegroup(name = "all", srcs = glob(["emulator/**"]))
+"""
+
+_SYSTEM_IMAGE_BUILD = """\
+package(default_visibility = ["//visibility:public"])
+
+exports_files(["system.img"])
+
+filegroup(name = "all", srcs = glob(["**"]))
+"""
+
+def _emulator_impl(_module_ctx):
+    http_archive(
+        name = "android_emulator",
+        build_file_content = _EMULATOR_BUILD,
+        sha256 = "25378c67fd5bd03178e3a478b866496da8545e969df3a7a26ce9167772ffc026",
+        url = "https://dl.google.com/android/repository/emulator-darwin_aarch64-15565763.zip",
+    )
+
+    # A regular GPU-enabled AOSP (default) image, not the headless ATD image.
+    http_archive(
+        name = "android_system_image",
+        build_file_content = _SYSTEM_IMAGE_BUILD,
+        sha256 = "1447958a4c6747c44390ac5f5f4c894be6d1dfce93868a0385a95c5f0ae4c339",
+        strip_prefix = "arm64-v8a",
+        url = "https://dl.google.com/android/repository/sys-img/android/arm64-v8a-34_r04.zip",
+    )
+
+emulator = module_extension(implementation = _emulator_impl)

examples/cross_compilation/android_app/run.sh

@@ -0,0 +1,80 @@
+#!/bin/bash
+# `bazel run //examples/cross_compilation/android_app:run`: installs the example
+# APK on a connected device/emulator and launches it. If nothing is connected,
+# boots the hermetic emulator (downloaded emulator + AOSP system image) first.
+set -euo pipefail
+
+RUNFILES_ROOT="$PWD/.."
+APK="$RUNFILES_ROOT/$1"
+ADB="$RUNFILES_ROOT/$2"
+EMULATOR_BIN="$RUNFILES_ROOT/$3"
+SYSIMG_MARKER="$RUNFILES_ROOT/$4"
+
+has_device() {
+  "$ADB" devices | awk 'NR>1 && $2 == "device"' | grep -q .
+}
+
+"$ADB" start-server >/dev/null 2>&1 || true
+
+if ! has_device; then
+  echo "No device connected; booting the hermetic emulator..."
+  EMULATOR_DIR="$(cd "$(dirname "$EMULATOR_BIN")" && pwd)"
+  SYSIMG_DIR="$(cd "$(dirname "$SYSIMG_MARKER")" && pwd)"
+
+  STATE="${TMPDIR:-/tmp}/rules_swift_android_example_emulator"
+  SDK="$STATE/sdk"
+  AVD_HOME="$STATE/avd"
+  AVD_DIR="$AVD_HOME/example.avd"
+  mkdir -p "$SDK/system-images/android-34/default" "$AVD_DIR" "$SDK/platform-tools"
+
+  ln -sfn "$EMULATOR_DIR" "$SDK/emulator"
+  ln -sfn "$SYSIMG_DIR" "$SDK/system-images/android-34/default/arm64-v8a"
+  ln -sfn "$ADB" "$SDK/platform-tools/adb"
+
+  cat > "$AVD_HOME/example.ini" <<EOF
+avd.ini.encoding=UTF-8
+path=$AVD_DIR
+target=android-34
+EOF
+
+  if [[ ! -f "$AVD_DIR/config.ini" ]]; then
+    cat > "$AVD_DIR/config.ini" <<EOF
+AvdId=example
+avd.ini.displayname=rules_swift Android example
+abi.type=arm64-v8a
+hw.cpu.arch=arm64
+image.sysdir.1=system-images/android-34/default/arm64-v8a/
+tag.id=default
+hw.gpu.enabled=yes
+hw.gpu.mode=auto
+hw.ramSize=2048
+hw.lcd.density=420
+hw.lcd.width=1080
+hw.lcd.height=1920
+PlayStore.enabled=false
+EOF
+  fi
+
+  export ANDROID_SDK_ROOT="$SDK"
+  export ANDROID_AVD_HOME="$AVD_HOME"
+  EMULATOR_LOG="$STATE/emulator.log"
+  "$SDK/emulator/emulator" -avd example -no-audio -no-boot-anim -no-snapshot >"$EMULATOR_LOG" 2>&1 &
+  echo "  (emulator log: $EMULATOR_LOG)"
+
+  "$ADB" wait-for-device
+  for _ in $(seq 1 120); do
+    # Wait for boot *and* the package manager (install races a "Broken pipe"
+    # otherwise, right after sys.boot_completed flips).
+    if [[ "$("$ADB" shell getprop sys.boot_completed 2>/dev/null | tr -d '\r')" == "1" ]] &&
+       "$ADB" shell pm path android >/dev/null 2>&1; then
+      break
+    fi
+    sleep 2
+  done
+  has_device || { echo "error: emulator failed to boot; see $EMULATOR_LOG" >&2; exit 1; }
+  echo "Emulator booted."
+fi
+
+"$ADB" install -r "$APK"
+"$ADB" shell am start -n "com.example.swiftjni/.MainActivity"
+echo "Launched com.example.swiftjni/.MainActivity"