Android: add cross-compilation flags

In addition to '--cross-compile-hosts', add two new bootstrap flags,
'--cross-compile-flags' and '--cross-compile-config', that will pass in a string
with cross-compilation flags and a JSON file with the destination flags. Even
though these two will be largely the same, both are needed because some
PackageDescription libraries are not built by SPM itself, so the string is
needed to build those with CMake.

Author: finagolfin

Utilities/bootstrap

@@ -143,6 +143,12 @@ def add_build_args(parser):
         dest="cross_compile_hosts",
         help="List of cross compile hosts targets.",
         default=[])
+    parser.add_argument(
+        "--cross-compile-flags",
+        help="Swift flags to cross-compile the PackageDescription libraries with CMake")
+    parser.add_argument(
+        "--cross-compile-config",
+        help="Swift flags to cross-compile SPM with itself")
 
 def add_test_args(parser):
     """Configures the parser with the arguments necessary for the test action."""
@@ -196,8 +202,14 @@ def parse_build_args(args):
     args.clang_path = get_clang_path(args)
     args.cmake_path = get_cmake_path(args)
     args.ninja_path = get_ninja_path(args)
-    if args.cross_compile_hosts: # Use XCBuild target directory when building for multiple arches.
-        args.target_dir = os.path.join(args.build_dir, "apple/Products")
+    if args.cross_compile_hosts:
+        if "macosx-arm64" in args.cross_compile_hosts:
+            # Use XCBuild target directory when building for multiple arches.
+            args.target_dir = os.path.join(args.build_dir, "apple/Products")
+        elif re.match('android-', args.cross_compile_hosts):
+            args.target_dir = os.path.join(
+                                  args.build_dir,
+                                  get_build_target(args,cross_compile=True))
     else:
         args.target_dir = os.path.join(args.build_dir, get_build_target(args))
     args.bootstrap_dir = os.path.join(args.target_dir, "bootstrap")
@@ -271,10 +283,18 @@ def get_ninja_path(args):
     else:
         return call_output(["which", "ninja"], verbose=args.verbose)
 
-def get_build_target(args):
+def get_build_target(args, cross_compile=False):
     """Returns the target-triple of the current machine."""
     try:
-        target_info_json = subprocess.check_output([args.swiftc_path, '-print-target-info'], stderr=subprocess.PIPE, universal_newlines=True).strip()
+        if cross_compile:
+            target_info_json = subprocess.check_output(
+                                   [args.swiftc_path, '-print-target-info'] +
+                                       args.cross_compile_flags.split(),
+                                   stderr=subprocess.PIPE, universal_newlines=True).strip()
+        else:
+            target_info_json = subprocess.check_output(
+                                   [args.swiftc_path, '-print-target-info'],
+                                   stderr=subprocess.PIPE, universal_newlines=True).strip()
         args.target_info = json.loads(target_info_json)
         return args.target_info["target"]["unversionedTriple"]
     except Exception as e:
@@ -309,8 +329,11 @@ def build(args):
         build_swift_argument_parser(args)
         build_swift_driver(args)
         build_swift_crypto(args)
+        build_swiftpm_with_cmake(args)
+
+    if args.cross_compile_flags:
+        build_packagedescription_libs_with_cmake(args)
 
-    build_swiftpm_with_cmake(args)
     build_swiftpm_with_swiftpm(args,integrated_swift_driver=False)
 
 def test(args):
@@ -459,11 +482,15 @@ def install_binary(args, binary, dest_dir):
 # Build functions
 # -----------------------------------------------------------
 
-def build_with_cmake(args, cmake_args, source_path, build_dir, targets=[]):
+def build_with_cmake(args, cmake_args, source_path, build_dir, targets=[], cross_compile=False):
     """Runs CMake if needed, then builds with Ninja."""
     cache_path = os.path.join(build_dir, "CMakeCache.txt")
     if args.reconfigure or not os.path.isfile(cache_path) or not args.swiftc_path in open(cache_path).read():
-        swift_flags = ""
+        if cross_compile:
+            swift_flags = args.cross_compile_flags
+        else:
+            swift_flags = ""
+
         if args.sysroot:
             swift_flags = "-sdk %s" % args.sysroot
 
@@ -593,30 +620,38 @@ def add_rpath_for_cmake_build(args, rpath):
     note(' '.join(add_rpath_cmd))
     subprocess.call(add_rpath_cmd, stderr=subprocess.PIPE)
 
+def build_packagedescription_libs_with_cmake(args):
+    """Builds the PackageDescription libraries using CMake."""
+    note("Building PackageDescription libraries (with CMake)")
+
+    cmake_flags = ["-DFIND_PM_DEPS:BOOL=NO"]
+    targets = ["PD4", "PD4_2", "PackagePlugin"]
+    if re.match('android-', args.cross_compile_hosts):
+        cmake_flags.append("-DCMAKE_SYSTEM_NAME=Android")
+        cmake_flags.append("-DCMAKE_SYSTEM_VERSION=1")
+
+    build_with_cmake(args, cmake_flags, args.project_root, args.bootstrap_dir,
+                     targets, cross_compile=True)
+
 def build_swiftpm_with_cmake(args):
     """Builds SwiftPM using CMake."""
     note("Building SwiftPM (with CMake)")
 
-    if args.bootstrap:
-        cmake_flags = [
-            get_llbuild_cmake_arg(args),
-            "-DTSC_DIR=" + os.path.join(args.tsc_build_dir, "cmake/modules"),
-            "-DYams_DIR=" + os.path.join(args.yams_build_dir, "cmake/modules"),
-            "-DArgumentParser_DIR=" + os.path.join(args.swift_argument_parser_build_dir, "cmake/modules"),
-            "-DSwiftDriver_DIR=" + os.path.join(args.swift_driver_build_dir, "cmake/modules"),
-            "-DSwiftCrypto_DIR=" + os.path.join(args.swift_crypto_build_dir, "cmake/modules"),
-            "-DFIND_PM_DEPS:BOOL=YES",
-        ]
-    else:
-        cmake_flags = [ "-DFIND_PM_DEPS:BOOL=NO" ]
+    cmake_flags = [
+        get_llbuild_cmake_arg(args),
+        "-DTSC_DIR=" + os.path.join(args.tsc_build_dir, "cmake/modules"),
+        "-DYams_DIR=" + os.path.join(args.yams_build_dir, "cmake/modules"),
+        "-DArgumentParser_DIR=" + os.path.join(args.swift_argument_parser_build_dir, "cmake/modules"),
+        "-DSwiftDriver_DIR=" + os.path.join(args.swift_driver_build_dir, "cmake/modules"),
+        "-DSwiftCrypto_DIR=" + os.path.join(args.swift_crypto_build_dir, "cmake/modules"),
+        "-DFIND_PM_DEPS:BOOL=YES",
+    ]
 
     if platform.system() == 'Darwin':
         cmake_flags.append("-DCMAKE_C_FLAGS=-target %s%s" % (get_build_target(args), g_macos_deployment_target))
         cmake_flags.append("-DCMAKE_OSX_DEPLOYMENT_TARGET=%s" % g_macos_deployment_target)
 
-    targets = [] if args.bootstrap else ["PD4", "PD4_2"]
-
-    build_with_cmake(args, cmake_flags, args.project_root, args.bootstrap_dir, targets)
+    build_with_cmake(args, cmake_flags, args.project_root, args.bootstrap_dir)
 
     if args.llbuild_link_framework:
         add_rpath_for_cmake_build(args, args.llbuild_build_dir)
@@ -792,7 +827,9 @@ def get_swiftpm_flags(args):
         )
 
     # Don't use GNU strerror_r on Android.
-    if 'ANDROID_DATA' in os.environ:
+    if 'ANDROID_DATA' in os.environ or
+        (args.cross_compile_hosts and
+         re.match('android-', args.cross_compile_hosts)):
         build_flags.extend(["-Xswiftc", "-Xcc", "-Xswiftc", "-U_GNU_SOURCE"])
 
     # On ELF platforms, remove the host toolchain's stdlib absolute rpath from
@@ -804,6 +841,8 @@ def get_swiftpm_flags(args):
     cross_compile_hosts = args.cross_compile_hosts
     if build_target == 'x86_64-apple-macosx' and "macosx-arm64" in cross_compile_hosts:
         build_flags += ["--arch", "x86_64", "--arch", "arm64"]
+    elif cross_compile_hosts and re.match('android-', cross_compile_hosts):
+        build_flags.extend(["--destination", args.cross_compile_config])
     elif cross_compile_hosts:
         error("cannot cross-compile for %s" % cross_compile_hosts)