fbcode_builder: getdeps: add platform type tuple helper

Summary:
This will feed into the manifest context for system
dependent manifest sections.  This is essentially the same
code borrowed from the watchman and eden getdeps.py.

Reviewed By: simpkins

Differential Revision: D14690997

fbshipit-source-id: 3d3ae146237a2cd49609aaa2bd0e785ebe21f02c

build/fbcode_builder/getdeps/test/platform_test.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python
+# Copyright (c) 2019-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree. An additional grant
+# of patent rights can be found in the PATENTS file in the same directory.
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import unittest
+
+from ..platform import HostType
+
+
+class PlatformTest(unittest.TestCase):
+    def test_create(self):
+        p = HostType()
+        self.assertNotEqual(p.ostype, None, msg="probed and returned something")
+
+        tuple_string = p.as_tuple_string()
+        round_trip = HostType.from_tuple_string(tuple_string)
+        self.assertEqual(round_trip, p)
+
+    def test_rendering_of_none(self):
+        p = HostType(ostype="foo")
+        self.assertEqual(p.as_tuple_string(), "foo-none-none")
+
+    def test_is_methods(self):
+        p = HostType(ostype="windows")
+        self.assertTrue(p.is_windows())
+        self.assertFalse(p.is_darwin())
+        self.assertFalse(p.is_linux())
+
+        p = HostType(ostype="darwin")
+        self.assertFalse(p.is_windows())
+        self.assertTrue(p.is_darwin())
+        self.assertFalse(p.is_linux())
+
+        p = HostType(ostype="linux")
+        self.assertFalse(p.is_windows())
+        self.assertFalse(p.is_darwin())
+        self.assertTrue(p.is_linux())