[Build System: build-script] Update the migration logic for the preset-only option '--swift-sdks' to execute in-place and support empty SDK lists.

utils/build-script

@@ -485,8 +485,8 @@ class BuildScriptInvocation(object):
             "--build-dir", self.workspace.build_root,
             "--install-prefix", args.install_prefix,
             "--host-target", args.host_target,
-            "--stdlib-deployment-targets",
-            " ".join(args.stdlib_deployment_targets),
+            "--stdlib-deployment-targets={}".format(
+                " ".join(args.stdlib_deployment_targets)),
             "--host-cc", toolchain.cc,
             "--host-cxx", toolchain.cxx,
             "--darwin-xcrun-toolchain", args.darwin_xcrun_toolchain,

utils/build_swift/migration.py

@@ -13,10 +13,19 @@
 
 from __future__ import absolute_import, unicode_literals
 
+import itertools
+
 from swift_build_support.swift_build_support.targets import \
     StdlibDeploymentTarget
 
 
+try:
+    # Python 2
+    from itertools import imap
+except ImportError:
+    imap = map
+
+
 __all__ = [
     'UnknownSDKError',
     'migrate_swift_sdks',
@@ -41,44 +50,41 @@ class UnknownSDKError(Exception):
     triples.
     """
 
-    pass
-
+    def __init__(self, sdk):
+        self.sdk = sdk
 
-def _swift_sdks_to_stdlib_targets(swift_sdks):
-    stdlib_targets = []
-    for sdk in swift_sdks:
-        sdk_targets = _SDK_TARGETS.get(sdk, None)
-        if sdk_targets is None:
-            raise UnknownSDKError(sdk)
-        stdlib_targets += sdk_targets
-
-    return stdlib_targets
+        super(UnknownSDKError, self).__init__(
+            'Unknown SDK: {}'.format(self.sdk))
 
 
 def migrate_swift_sdks(args):
     """Migrate usages of the now deprecated `--swift-sdks` option to the new
     `--stdlib-deployment-targets` option, converting Swift SDKs to the
-    corresponding targets. Since argument parsing is a last-wins scenario, only
-    the last `--swift-sdks` option is migrated, all others are removed.
+    corresponding targets.
 
     This function is a stop-gap to replacing all instances of `--swift-sdks`.
     """
 
-    swift_sdks_args = [arg for arg in args if arg.startswith('--swift-sdks')]
+    def _flatten(iterable):
+        return itertools.chain.from_iterable(iterable)
+
+    def _swift_sdk_to_stdlib_targets(sdk):
+        targets = _SDK_TARGETS.get(sdk, None)
+        if targets is None:
+            raise UnknownSDKError(sdk)
 
-    if len(swift_sdks_args) < 1:
-        return args
+        return targets
 
-    # Only get the last --swift-sdks arg since last-wins
-    swift_sdks_arg = swift_sdks_args[-1]
+    def _migrate_swift_sdks_arg(arg):
+        if not arg.startswith('--swift-sdks'):
+            return arg
 
-    sdk_list = swift_sdks_arg.split('=')[1].split(';')
-    stdlib_targets = _swift_sdks_to_stdlib_targets(sdk_list)
+        sdks = arg.split('=')[1]
+        sdk_list = [] if sdks == '' else sdks.split(';')
 
-    target_names = ' '.join([target.name for target in stdlib_targets])
-    stdlib_targets_arg = '--stdlib-deployment-targets=' + target_names
+        targets = _flatten(imap(_swift_sdk_to_stdlib_targets, sdk_list))
+        target_names = [target.name for target in targets]
 
-    args = [arg for arg in args if not arg.startswith('--swift-sdks')]
-    args.append(stdlib_targets_arg)
+        return '--stdlib-deployment-targets={}'.format(' '.join(target_names))
 
-    return args
+    return list(imap(_migrate_swift_sdks_arg, args))

utils/build_swift/tests/test_migration.py

@@ -57,15 +57,22 @@ def test(self):
 @add_metaclass(TestMigrateSwiftSDKsMeta)
 class TestMigrateSwiftSDKs(TestCase):
 
+    def test_empty_swift_sdks(self):
+        args = migration.migrate_swift_sdks(['--swift-sdks='])
+        self.assertListEqual(args, ['--stdlib-deployment-targets='])
+
     def test_multiple_swift_sdk_flags(self):
+        sdks = ['OSX', 'IOS', 'IOS_SIMULATOR']
+
         args = [
-            '--swift-sdks=OSX',
-            '--swift-sdks=OSX;IOS;IOS_SIMULATOR'
+            '--swift-sdks=',
+            '--swift-sdks={}'.format(';'.join(sdks))
         ]
 
         args = migration.migrate_swift_sdks(args)
-        target_names = _get_sdk_target_names(['OSX', 'IOS', 'IOS_SIMULATOR'])
+        target_names = _get_sdk_target_names(sdks)
 
         self.assertListEqual(args, [
+            '--stdlib-deployment-targets=',
             '--stdlib-deployment-targets={}'.format(' '.join(target_names))
         ])