From 8dcbea9675f66787ef3c560ff17e45f8932964ce Mon Sep 17 00:00:00 2001
From: Ron Buckton <rbuckton@microsoft.com>
Date: Wed, 7 Dec 2016 17:17:17 -0800
Subject: [PATCH] Fix await for inherited promise

---
 src/compiler/checker.ts                          |  2 +-
 .../reference/awaitInheritedPromise_es2017.js    | 11 +++++++++++
 .../awaitInheritedPromise_es2017.symbols         | 15 +++++++++++++++
 .../reference/awaitInheritedPromise_es2017.types | 16 ++++++++++++++++
 .../async/es2017/awaitInheritedPromise_es2017.ts |  7 +++++++
 5 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/awaitInheritedPromise_es2017.js
 create mode 100644 tests/baselines/reference/awaitInheritedPromise_es2017.symbols
 create mode 100644 tests/baselines/reference/awaitInheritedPromise_es2017.types
 create mode 100644 tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index cdef31ee400..dc97d347e95 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -16207,7 +16207,7 @@ namespace ts {
                 return undefined;
             }
 
-            const onfulfilledParameterType = getTypeWithFacts(getUnionType(map(thenSignatures, getTypeOfFirstParameterOfSignature)), TypeFacts.NEUndefined);
+            const onfulfilledParameterType = getTypeWithFacts(getUnionType(map(thenSignatures, getTypeOfFirstParameterOfSignature)), TypeFacts.NEUndefinedOrNull);
             if (isTypeAny(onfulfilledParameterType)) {
                 return undefined;
             }
diff --git a/tests/baselines/reference/awaitInheritedPromise_es2017.js b/tests/baselines/reference/awaitInheritedPromise_es2017.js
new file mode 100644
index 00000000000..e973d0b166a
--- /dev/null
+++ b/tests/baselines/reference/awaitInheritedPromise_es2017.js
@@ -0,0 +1,11 @@
+//// [awaitInheritedPromise_es2017.ts]
+interface A extends Promise<string> {}
+declare var a: A;
+async function f() {
+    await a;
+}
+
+//// [awaitInheritedPromise_es2017.js]
+async function f() {
+    await a;
+}
diff --git a/tests/baselines/reference/awaitInheritedPromise_es2017.symbols b/tests/baselines/reference/awaitInheritedPromise_es2017.symbols
new file mode 100644
index 00000000000..ef68d16b678
--- /dev/null
+++ b/tests/baselines/reference/awaitInheritedPromise_es2017.symbols
@@ -0,0 +1,15 @@
+=== tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts ===
+interface A extends Promise<string> {}
+>A : Symbol(A, Decl(awaitInheritedPromise_es2017.ts, 0, 0))
+>Promise : Symbol(Promise, Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --))
+
+declare var a: A;
+>a : Symbol(a, Decl(awaitInheritedPromise_es2017.ts, 1, 11))
+>A : Symbol(A, Decl(awaitInheritedPromise_es2017.ts, 0, 0))
+
+async function f() {
+>f : Symbol(f, Decl(awaitInheritedPromise_es2017.ts, 1, 17))
+
+    await a;
+>a : Symbol(a, Decl(awaitInheritedPromise_es2017.ts, 1, 11))
+}
diff --git a/tests/baselines/reference/awaitInheritedPromise_es2017.types b/tests/baselines/reference/awaitInheritedPromise_es2017.types
new file mode 100644
index 00000000000..bed681181b0
--- /dev/null
+++ b/tests/baselines/reference/awaitInheritedPromise_es2017.types
@@ -0,0 +1,16 @@
+=== tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts ===
+interface A extends Promise<string> {}
+>A : A
+>Promise : Promise<T>
+
+declare var a: A;
+>a : A
+>A : A
+
+async function f() {
+>f : () => Promise<void>
+
+    await a;
+>await a : string
+>a : A
+}
diff --git a/tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts b/tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts
new file mode 100644
index 00000000000..c5cd486e0f0
--- /dev/null
+++ b/tests/cases/conformance/async/es2017/awaitInheritedPromise_es2017.ts
@@ -0,0 +1,7 @@
+// @target: es2017
+// @strictNullChecks: true
+interface A extends Promise<string> {}
+declare var a: A;
+async function f() {
+    await a;
+}
\ No newline at end of file