Make Android build optional on Nix (#31231)

* Make Android build optional on Nix

I want to build Servo without also installing the entire Android SDK.
This makes it so Android support is only built if `buildAndroid` is
true.

Signed-off-by: syvb <me@iter.ca>

* Add Android support to nix-shell if SERVO_ANDROID_BUILD set

---------

Signed-off-by: syvb <me@iter.ca>

etc/shell.nix

@@ -1,6 +1,9 @@
 # This provides a shell with all the necesarry packages required to run mach and build servo
 # NOTE: This does not work offline or for nix-build
 
+{
+  buildAndroid ? false
+}:
 with import (builtins.fetchTarball {
   url = "https://github.com/NixOS/nixpkgs/archive/46ae0210ce163b3cba6c7da08840c1d63de9c701.tar.gz";
 }) {
@@ -11,8 +14,8 @@ with import (builtins.fetchTarball {
     }))
   ];
   config = {
-    android_sdk.accept_license = true;
+    android_sdk.accept_license = buildAndroid;
-    allowUnfree = true;
+    allowUnfree = buildAndroid;
   };
 };
 let
@@ -134,22 +137,16 @@ stdenv.mkDerivation rec {
 
       RUSTC_BOOTSTRAP = "crown";
     }))
-
-    # for android builds
-    # TODO: make this optional
-    openjdk17_headless
-    androidSdk
   ] ++ (lib.optionals stdenv.isDarwin [
     darwin.apple_sdk.frameworks.AppKit
+  ]) ++ (lib.optionals buildAndroid [
+    # for android builds
+    openjdk17_headless
+    androidSdk
   ]);
 
   LIBCLANG_PATH = llvmPackages.clang-unwrapped.lib + "/lib/";
 
-  # Required by ./mach build --android
-  ANDROID_SDK_ROOT = "${androidSdk}/libexec/android-sdk";
-  ANDROID_NDK_ROOT = "${ANDROID_SDK_ROOT}/ndk-bundle";
-  GRADLE_OPTS = "-Dorg.gradle.project.android.aapt2FromMavenOverride=${ANDROID_SDK_ROOT}/build-tools/${buildToolsVersion}/aapt2";
-
   # Allow cargo to download crates
   SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
 
@@ -217,4 +214,9 @@ stdenv.mkDerivation rec {
       export RUSTUP_HOME=$repo_root/.rustup
     fi
   '';
+} // lib.optionalAttrs buildAndroid {
+  # Required by ./mach build --android
+  ANDROID_SDK_ROOT = "${androidSdk}/libexec/android-sdk";
+  ANDROID_NDK_ROOT = "${ANDROID_SDK_ROOT}/ndk-bundle";
+  GRADLE_OPTS = "-Dorg.gradle.project.android.aapt2FromMavenOverride=${ANDROID_SDK_ROOT}/build-tools/${buildToolsVersion}/aapt2";
 }

mach

@@ -36,10 +36,11 @@ if __name__ == '__main__':
         import subprocess
         from shlex import quote
         mach_dir = os.path.abspath(os.path.dirname(__file__))
+        build_android_args = ['--arg', 'buildAndroid', 'true'] if 'SERVO_ANDROID_BUILD' in os.environ else []
         print('NOTE: Entering nix-shell etc/shell.nix')
         try:
             # sys argv already contains the ./mach part, so we just need to pass it as-is
-            result = subprocess.run(['nix-shell', mach_dir + '/etc/shell.nix', '--run', ' '.join(map(quote, sys.argv))])
+            result = subprocess.run(['nix-shell', mach_dir + '/etc/shell.nix'] + build_android_args + ['--run', ' '.join(map(quote, sys.argv))])
             sys.exit(result.returncode)
         except KeyboardInterrupt:
             sys.exit(0)

python/servo/command_base.py

@@ -537,6 +537,9 @@ class CommandBase(object):
             if os.path.isdir(default):
                 env.setdefault(f"ANDROID_{kind.upper()}_ROOT", default)
 
+        if "IN_NIX_SHELL" in env and ("ANDROID_NDK_ROOT" not in env or "ANDROID_SDK_ROOT" not in env):
+            print("Please set SERVO_ANDROID_BUILD=1 when starting the Nix shell to include the Android SDK/NDK.")
+            sys.exit(1)
         if "ANDROID_NDK_ROOT" not in env:
             print("Please set the ANDROID_NDK_ROOT environment variable.")
             sys.exit(1)