Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/android/apk_genrule.bzl

@@ -0,0 +1,35 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under both the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree and the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree.
+
+load("@prelude//:genrule.bzl", "process_genrule")
+load("@prelude//android:android_providers.bzl", "AndroidApkInfo", "AndroidApkUnderTestInfo")
+load("@prelude//utils:utils.bzl", "expect")
+
+def apk_genrule_impl(ctx: "context") -> ["provider"]:
+    # TODO(T104150125) The underlying APK should not have exopackage enabled
+    input_android_apk_info = ctx.attrs.apk[AndroidApkInfo]
+    expect(input_android_apk_info != None, "'apk' attribute must be an Android APK!")
+    input_android_apk_under_test_info = ctx.attrs.apk[AndroidApkUnderTestInfo]
+
+    env_vars = {
+        "APK": cmd_args(input_android_apk_info.apk),
+    }
+
+    # Like buck1, we ignore the 'out' attribute and construct the output path ourselves.
+    output_apk_name = "{}.apk".format(ctx.label.name)
+
+    genrule_providers = process_genrule(ctx, output_apk_name, None, env_vars)
+
+    expect(len(genrule_providers) == 1 and type(genrule_providers[0]) == DefaultInfo.type, "Expecting just a single DefaultInfo, but got {}".format(genrule_providers))
+    output_apk = genrule_providers[0].default_outputs[0]
+
+    return genrule_providers + [
+        AndroidApkInfo(
+            apk = output_apk,
+            manifest = input_android_apk_info.manifest,
+        ),
+    ] + filter(None, [input_android_apk_under_test_info])