[build-script-helper] Add support for Android cross-compilation

Add new flags '--cross-compile-host' and '--cross-compile-config' and use them to
cross-compile, gated only for Android for now. Add a '--prefix' flag to install
to a cross-compiled toolchain instead and set 'SWIFT_EXEC' when using SPM, so it
uses the right Swift toolchain.

Author: finagolfin

Utilities/build-script-helper.py

@@ -5,6 +5,7 @@
 import argparse
 import os
 import platform
+import re
 import shutil
 import subprocess
 import sys
@@ -50,25 +51,28 @@ def get_swiftpm_options(args):
       os.path.join(args.toolchain, 'lib', 'swift', 'Block'),
     ]
 
-    if 'ANDROID_DATA' in os.environ:
-      swiftpm_args += [
-        '-Xlinker', '-rpath', '-Xlinker', '$ORIGIN/../lib/swift/android',
-        # SwiftPM will otherwise try to compile against GNU strerror_r on
-        # Android and fail.
-        '-Xswiftc', '-Xcc', '-Xswiftc', '-U_GNU_SOURCE',
-      ]
-    else:
-      # Library rpath for swift, dispatch, Foundation, etc. when installing
-      swiftpm_args += [
-        '-Xlinker', '-rpath', '-Xlinker', '$ORIGIN/../lib/swift/linux',
-      ]
+  if 'ANDROID_DATA' in os.environ or (args.cross_compile_host and re.match(
+    'android-', args.cross_compile_host)):
+    swiftpm_args += [
+      '-Xlinker', '-rpath', '-Xlinker', '$ORIGIN/../lib/swift/android',
+      # SwiftPM will otherwise try to compile against GNU strerror_r on
+      # Android and fail.
+      '-Xswiftc', '-Xcc', '-Xswiftc', '-U_GNU_SOURCE',
+    ]
+  elif platform.system() == 'Linux':
+    # Library rpath for swift, dispatch, Foundation, etc. when installing
+    swiftpm_args += [
+      '-Xlinker', '-rpath', '-Xlinker', '$ORIGIN/../lib/swift/linux',
+    ]
+
+  if args.cross_compile_host:
+    swiftpm_args += ['--destination', args.cross_compile_config]
 
   return swiftpm_args
 
-def install(swiftpm_bin_path, toolchain):
-  toolchain_bin = os.path.join(toolchain, 'bin')
-  for exe in ['sourcekit-lsp']:
-    install_binary(exe, swiftpm_bin_path, toolchain_bin, toolchain)
+def install(swiftpm_bin_path, prefixes, toolchain):
+  for prefix in prefixes:
+    install_binary('sourcekit-lsp', swiftpm_bin_path, os.path.join(prefix, 'bin'), toolchain)
 
 def install_binary(exe, source_dir, install_dir, toolchain):
   cmd = ['rsync', '-a', os.path.join(source_dir, exe), install_dir]
@@ -112,6 +116,8 @@ def handle_invocation(swift_exec, args):
   print('Cleaning ' + args.build_path)
   shutil.rmtree(args.build_path, ignore_errors=True)
 
+  env['SWIFT_EXEC'] = '%sc' % (swift_exec)
+
   if args.action == 'build':
     swiftpm('build', swift_exec, swiftpm_args, env)
   elif args.action == 'test':
@@ -131,7 +137,10 @@ def handle_invocation(swift_exec, args):
     bin_path = swiftpm_bin_path(swift_exec, swiftpm_args, env)
     swiftpm_args += ['-Xswiftc', '-no-toolchain-stdlib-rpath']
     swiftpm('build', swift_exec, swiftpm_args, env)
-    install(bin_path, args.toolchain)
+
+    if not args.install_prefixes:
+      args.install_prefixes = [args.toolchain]
+    install(bin_path, args.install_prefixes, args.toolchain)
   else:
     assert False, 'unknown action \'{}\''.format(args.action)
 
@@ -148,6 +157,8 @@ def add_common_args(parser):
     parser.add_argument('--sanitize', action='append', help='build using the given sanitizer(s) (address|thread|undefined)')
     parser.add_argument('--sanitize-all', action='store_true', help='build using every available sanitizer in sub-directories of build path')
     parser.add_argument('--verbose', '-v', action='store_true', help='enable verbose output')
+    parser.add_argument('--cross-compile-host', help='cross-compile for another host instead')
+    parser.add_argument('--cross-compile-config', help='an SPM JSON destination file containing Swift cross-compilation flags')
 
   subparsers = parser.add_subparsers(title='subcommands', dest='action', metavar='action')
   build_parser = subparsers.add_parser('build', help='build the package')
@@ -159,6 +170,7 @@ def add_common_args(parser):
 
   install_parser = subparsers.add_parser('install', help='build the package')
   add_common_args(install_parser)
+  install_parser.add_argument('--prefix', dest='install_prefixes', nargs='*', metavar='PATHS', help="paths to install sourcekit-lsp, default: 'toolchain/bin'")
 
   args = parser.parse_args(sys.argv[1:])
 
@@ -175,6 +187,11 @@ def add_common_args(parser):
   else:
     swift_exec = 'swift'
 
+  if args.cross_compile_host and re.match('android-', args.cross_compile_host):
+    print('Cross-compiling for %s' % args.cross_compile_host)
+  elif args.cross_compile_host:
+    error("cannot cross-compile for %s" % args.cross_compile_host)
+
   handle_invocation(swift_exec, args)
   if args.sanitize_all:
     base = args.build_path