From 17acef12bcf155cd55559174345801d919ac3e10 Mon Sep 17 00:00:00 2001
From: David Fisher <ddfisher@dropbox.com>
Date: Mon, 8 Aug 2016 14:59:47 -0700
Subject: [PATCH 1/2] Make join(None, T) produce Optional[T]

---
 mypy/join.py                       | 10 +++++++++-
 test-data/unit/check-optional.test |  8 ++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/mypy/join.py b/mypy/join.py
index d63388d35450..8dd97d20b0ae 100644
--- a/mypy/join.py
+++ b/mypy/join.py
@@ -66,6 +66,9 @@ def join_types(s: Type, t: Type) -> Type:
     if isinstance(s, ErasedType):
         return t
 
+    if isinstance(s, UnionType) and not isinstance(t, UnionType):
+        s, t = t, s
+
     if isinstance(s, NoneTyp) and not isinstance(t, NoneTyp):
         s, t = t, s
 
@@ -73,6 +76,7 @@ def join_types(s: Type, t: Type) -> Type:
     return t.accept(TypeJoinVisitor(s))
 
 
+
 class TypeJoinVisitor(TypeVisitor[Type]):
     """Implementation of the least upper bound algorithm.
 
@@ -114,8 +118,12 @@ def visit_none_type(self, t: NoneTyp) -> Type:
         if experiments.STRICT_OPTIONAL:
             if isinstance(self.s, (NoneTyp, UninhabitedType)):
                 return t
+            elif isinstance(self.s, UnboundType):
+                return AnyType()
+            elif isinstance(self.s, Void) or isinstance(self.s, ErrorType):
+                return ErrorType()
             else:
-                return self.default(self.s)
+                return UnionType.make_simplified_union([self.s, t])
         else:
             if not isinstance(self.s, Void):
                 return self.s
diff --git a/test-data/unit/check-optional.test b/test-data/unit/check-optional.test
index 2d643fea4648..7c6b3b3a4fae 100644
--- a/test-data/unit/check-optional.test
+++ b/test-data/unit/check-optional.test
@@ -330,3 +330,11 @@ def lookup_field(name, obj):
 [out]
 main: note: In function "lookup_field":
 main:10: error: Need type annotation for variable
+
+[case testTernaryWithNone]
+reveal_type(None if bool() else 0)  # E: Revealed type is 'Union[builtins.int, builtins.None]'
+[builtins fixtures/bool.py]
+
+[case testListWithNone]
+reveal_type([0, None, 0])    # E: Revealed type is 'builtins.list[Union[builtins.int, builtins.None]]'
+[builtins fixtures/list.py]

From 93b57cfe71bc70598dcd668a842214c4b2d00763 Mon Sep 17 00:00:00 2001
From: David Fisher <ddfisher@dropbox.com>
Date: Mon, 8 Aug 2016 16:00:45 -0700
Subject: [PATCH 2/2] remove extraneous blank line

---
 mypy/join.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mypy/join.py b/mypy/join.py
index 8dd97d20b0ae..d6ca21448e41 100644
--- a/mypy/join.py
+++ b/mypy/join.py
@@ -76,7 +76,6 @@ def join_types(s: Type, t: Type) -> Type:
     return t.accept(TypeJoinVisitor(s))
 
 
-
 class TypeJoinVisitor(TypeVisitor[Type]):
     """Implementation of the least upper bound algorithm.