From 252840ad40f33518b5efd47a9d2a9c7c8d1514ab Mon Sep 17 00:00:00 2001
From: Andrew Branch <andrew@wheream.io>
Date: Mon, 24 Jun 2019 17:37:14 -0700
Subject: [PATCH] Fix incorrect noImplicitAny error on contextual union
 function signature

---
 src/compiler/checker.ts                             |  4 +++-
 .../functionExpressionContextualTyping3.js          |  8 ++++++++
 .../functionExpressionContextualTyping3.symbols     | 12 ++++++++++++
 .../functionExpressionContextualTyping3.types       | 13 +++++++++++++
 .../functionExpressionContextualTyping3.ts          |  5 +++++
 5 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/functionExpressionContextualTyping3.js
 create mode 100644 tests/baselines/reference/functionExpressionContextualTyping3.symbols
 create mode 100644 tests/baselines/reference/functionExpressionContextualTyping3.types
 create mode 100644 tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping3.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index a3abe1dc5b5..534e5e2f067 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -19095,7 +19095,9 @@ namespace ts {
                 }
             }
             // Result is union of signatures collected (return type is union of return types of this signature set)
-            return signatureList && createUnionSignature(signatureList[0], signatureList);
+            if (signatureList) {
+                return signatureList.length === 1 ? signatureList[0] : createUnionSignature(signatureList[0], signatureList);
+            }
         }
 
         function checkSpreadExpression(node: SpreadElement, checkMode?: CheckMode): Type {
diff --git a/tests/baselines/reference/functionExpressionContextualTyping3.js b/tests/baselines/reference/functionExpressionContextualTyping3.js
new file mode 100644
index 00000000000..b25754b568f
--- /dev/null
+++ b/tests/baselines/reference/functionExpressionContextualTyping3.js
@@ -0,0 +1,8 @@
+//// [functionExpressionContextualTyping3.ts]
+// #31114
+declare function f<T>(value: T | number): void;
+f((a: any) => "")
+
+
+//// [functionExpressionContextualTyping3.js]
+f(function (a) { return ""; });
diff --git a/tests/baselines/reference/functionExpressionContextualTyping3.symbols b/tests/baselines/reference/functionExpressionContextualTyping3.symbols
new file mode 100644
index 00000000000..8b773f08428
--- /dev/null
+++ b/tests/baselines/reference/functionExpressionContextualTyping3.symbols
@@ -0,0 +1,12 @@
+=== tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping3.ts ===
+// #31114
+declare function f<T>(value: T | number): void;
+>f : Symbol(f, Decl(functionExpressionContextualTyping3.ts, 0, 0))
+>T : Symbol(T, Decl(functionExpressionContextualTyping3.ts, 1, 19))
+>value : Symbol(value, Decl(functionExpressionContextualTyping3.ts, 1, 22))
+>T : Symbol(T, Decl(functionExpressionContextualTyping3.ts, 1, 19))
+
+f((a: any) => "")
+>f : Symbol(f, Decl(functionExpressionContextualTyping3.ts, 0, 0))
+>a : Symbol(a, Decl(functionExpressionContextualTyping3.ts, 2, 3))
+
diff --git a/tests/baselines/reference/functionExpressionContextualTyping3.types b/tests/baselines/reference/functionExpressionContextualTyping3.types
new file mode 100644
index 00000000000..662aa72ea90
--- /dev/null
+++ b/tests/baselines/reference/functionExpressionContextualTyping3.types
@@ -0,0 +1,13 @@
+=== tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping3.ts ===
+// #31114
+declare function f<T>(value: T | number): void;
+>f : <T>(value: number | T) => void
+>value : number | T
+
+f((a: any) => "")
+>f((a: any) => "") : void
+>f : <T>(value: number | T) => void
+>(a: any) => "" : (a: any) => ""
+>a : any
+>"" : ""
+
diff --git a/tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping3.ts b/tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping3.ts
new file mode 100644
index 00000000000..a1dc4e5d7d7
--- /dev/null
+++ b/tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping3.ts
@@ -0,0 +1,5 @@
+// @noImplicitAny: true
+
+// #31114
+declare function f<T>(value: T | number): void;
+f((a: any) => "")