[osx_sdk] Fix properties when setting a single value.

Because of the (unfortunate) ways that PROPERTIES works currently,
setting defaults in the obvious way means that providing a subset of the
values as properties replaces the defaults entirely.

In this case we want to override the sdk_version without having to
override the toolchain app version.

R=jchinlee@chromium.org, tandrii@chromium.org

Change-Id: I13f4ee19e45a3bb147b37f69d10cb4ed4f734a21
Reviewed-on: https://chromium-review.googlesource.com/c/1438088
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Auto-Submit: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>

recipes/README.recipes.md

@@ -670,11 +670,11 @@ XCode installation.
 
 Available only to Google-run bots.
 
-#### **class [OSXSDKApi](/recipes/recipe_modules/osx_sdk/api.py#15)([RecipeApi][recipe_engine/wkt/RecipeApi]):**
+#### **class [OSXSDKApi](/recipes/recipe_modules/osx_sdk/api.py#24)([RecipeApi][recipe_engine/wkt/RecipeApi]):**
 
 API for using OS X SDK distributed via CIPD.
 
-&emsp; **@contextmanager**<br>&mdash; **def [\_\_call\_\_](/recipes/recipe_modules/osx_sdk/api.py#25)(self, kind):**
+&emsp; **@contextmanager**<br>&mdash; **def [\_\_call\_\_](/recipes/recipe_modules/osx_sdk/api.py#37)(self, kind):**
 
 Sets up the XCode SDK environment.
 

recipes/recipe_modules/osx_sdk/__init__.py

@@ -30,11 +30,6 @@ PROPERTIES = {
       # The CIPD toolchain tool package and version
       toolchain_pkg=Single(str),
       toolchain_ver=Single(str),
-    ), default={
-      'sdk_version': '9c40b',
-
-      'toolchain_pkg': 'infra/tools/mac_toolchain/${platform}',
-      'toolchain_ver': 'git_revision:796d2b92cff93fc2059623ce0a66284373ceea0a',
-    },
+    ), default={},
   )
 }

recipes/recipe_modules/osx_sdk/api.py

@@ -11,6 +11,15 @@ from contextlib import contextmanager
 
 from recipe_engine import recipe_api
 
+# TODO(iannucci): replace this with something sane when PROPERTIES is
+# implemented with a proto message.
+_PROPERTY_DEFAULTS = {
+  'sdk_version': '9c40b',
+
+  'toolchain_pkg': 'infra/tools/mac_toolchain/${platform}',
+  'toolchain_ver': 'git_revision:796d2b92cff93fc2059623ce0a66284373ceea0a',
+}
+
 
 class OSXSDKApi(recipe_api.RecipeApi):
   """API for using OS X SDK distributed via CIPD."""
@@ -18,9 +27,12 @@ class OSXSDKApi(recipe_api.RecipeApi):
   def __init__(self, sdk_properties, *args, **kwargs):
     super(OSXSDKApi, self).__init__(*args, **kwargs)
 
-    self._sdk_version = sdk_properties['sdk_version'].lower()
-    self._tool_pkg = sdk_properties['toolchain_pkg']
-    self._tool_ver = sdk_properties['toolchain_ver']
+    actual_props = _PROPERTY_DEFAULTS.copy()
+    actual_props.update(sdk_properties)
+
+    self._sdk_version = actual_props['sdk_version'].lower()
+    self._tool_pkg = actual_props['toolchain_pkg']
+    self._tool_ver = actual_props['toolchain_ver']
 
   @contextmanager
   def __call__(self, kind):