Fix __deprecated_attributes__ usage

- The dict needs to live in the module where the deprecated attributes
  are; so here it needs to be hazmat.__deprecated_attributes__.
  (Maybe it would be less confusing to put this in hazmat.py, I don't
  know.)

- Don't export the symbols from trio.hazmat using normal mechanisms;
  that overrides the __deprecated_attributes__ mechanism.

- Then since they're no longer in hazmat, we can't say that
  trio.hazmat.Value resolves to the value trio.hazmat.Value, so point
  the __deprecated_attributes__ entries directly at trio._core._result.*

- In fact, let's stop exporting them from trio._core entirely.

- And then this reveals two tests that were still referring to
  trio._core.Error, so fix those.

Confirmed manually that with these changes I get correct values and
warnings for accessing the public attributes:

In [2]: trio.hazmat.Result
/home/njs/.user-python3.5-64bit/bin/ipython:1: TrioDeprecationWarning: trio.hazmat.Result is deprecated since Trio 0.5.0; use outcome.Outcome instead (#494)
  #!/home/njs/.user-python3.5-64bit/bin/python3.5
Out[2]: trio._core._result.Result  # class

In [3]: trio.hazmat.Value
/home/njs/.user-python3.5-64bit/bin/ipython:1: TrioDeprecationWarning: trio.hazmat.Value is deprecated since Trio 0.5.0; use outcome.Value instead (#494)
  #!/home/njs/.user-python3.5-64bit/bin/python3.5
Out[3]: outcome.Value  # class

In [4]: trio.hazmat.Error
/home/njs/.user-python3.5-64bit/bin/ipython:1: TrioDeprecationWarning: trio.hazmat.Error is deprecated since Trio 0.5.0; use outcome.Error instead (#494)
  #!/home/njs/.user-python3.5-64bit/bin/python3.5
Out[4]: outcome.Error  # class

trio/__init__.py

@@ -65,20 +65,25 @@
 from . import abc
 from . import ssl
 # Not imported by default: testing
+
 _deprecate.enable_attribute_deprecations(hazmat.__name__)
 
-__deprecated_attributes__ = {
+# Temporary hack to make sure _result is loaded, just during the deprecation
+# period
+from ._core import _result
+
+hazmat.__deprecated_attributes__ = {
     "Result":
         _deprecate.DeprecatedAttribute(
-            hazmat.Result, "0.5.0", issue=494, instead="outcome.Outcome"
+            _core._result.Result, "0.5.0", issue=494, instead="outcome.Outcome"
         ),
     "Value":
         _deprecate.DeprecatedAttribute(
-            hazmat.Value, "0.5.0", issue=494, instead="outcome.Value"
+            _core._result.Value, "0.5.0", issue=494, instead="outcome.Value"
         ),
     "Error":
         _deprecate.DeprecatedAttribute(
-            hazmat.Error, "0.5.0", issue=494, instead="outcome.Error"
+            _core._result.Error, "0.5.0", issue=494, instead="outcome.Error"
         )
 }
 

trio/_core/__init__.py

@@ -15,9 +15,6 @@ def _public(fn):
 from ._multierror import *
 __all__ += _multierror.__all__
 
-from ._result import *
-__all__ += _result.__all__
-
 from ._traps import *
 __all__ += _traps.__all__
 

trio/_core/tests/test_run.py

@@ -1106,7 +1106,7 @@ async def child():
         async with _core.open_nursery() as nursery:
             nursery.start_soon(child)
             await wait_all_tasks_blocked()
-            _core.reschedule(child_task, _core.Error(ValueError()))
+            _core.reschedule(child_task, outcome.Error(ValueError()))
 
 
 # Similar to previous test -- if the ValueError() gets sent in via 'throw',
@@ -1127,7 +1127,7 @@ async def child():
         async with _core.open_nursery() as nursery:
             nursery.start_soon(child)
             await wait_all_tasks_blocked()
-            _core.reschedule(child_task, _core.Error(ValueError()))
+            _core.reschedule(child_task, outcome.Error(ValueError()))
 
     assert isinstance(excinfo.value.__context__, KeyError)
 

trio/hazmat.py

@@ -3,9 +3,6 @@
 # symbols, and then we prune some below if they aren't available on this
 # system.
 __all__ = [
-    "Result",
-    "Value",
-    "Error",
     "cancel_shielded_checkpoint",
     "Abort",
     "wait_task_rescheduled",