From 2cf7295c4ee1a1864742287138416c502ec84f55 Mon Sep 17 00:00:00 2001
From: Ryan Cavanaugh <RyanCavanaugh@users.noreply.github.com>
Date: Wed, 6 Dec 2017 16:21:18 -0800
Subject: [PATCH] Fix #20520

---
 src/services/codefixes/inferFromUsage.ts                | 9 +++++++--
 tests/cases/fourslash/incompleteFunctionCallCodefix2.ts | 7 +++++++
 2 files changed, 14 insertions(+), 2 deletions(-)
 create mode 100644 tests/cases/fourslash/incompleteFunctionCallCodefix2.ts

diff --git a/src/services/codefixes/inferFromUsage.ts b/src/services/codefixes/inferFromUsage.ts
index d7bfd1b621f..25236318612 100644
--- a/src/services/codefixes/inferFromUsage.ts
+++ b/src/services/codefixes/inferFromUsage.ts
@@ -196,8 +196,9 @@ namespace ts.codefix {
             sourceFile,
             token.getStart(sourceFile));
 
-        Debug.assert(!!references, "Found no references!");
-        Debug.assert(references.length === 1, "Found more references than expected");
+        if (!references || references.length !== 1) {
+            return [];
+        }
 
         return references[0].references.map(r => <Identifier>getTokenAtPosition(program.getSourceFile(r.fileName), r.textSpan.start, /*includeJsDocComment*/ false));
     }
@@ -286,6 +287,10 @@ namespace ts.codefix {
         }
 
         export function inferTypeForParametersFromReferences(references: Identifier[], declaration: FunctionLikeDeclaration, checker: TypeChecker, cancellationToken: CancellationToken): (Type | undefined)[] | undefined {
+            if (references.length === 0) {
+                return undefined;
+            }
+
             if (declaration.parameters) {
                 const usageContext: UsageContext = {};
                 for (const reference of references) {
diff --git a/tests/cases/fourslash/incompleteFunctionCallCodefix2.ts b/tests/cases/fourslash/incompleteFunctionCallCodefix2.ts
new file mode 100644
index 00000000000..c1bc731541f
--- /dev/null
+++ b/tests/cases/fourslash/incompleteFunctionCallCodefix2.ts
@@ -0,0 +1,7 @@
+/// <reference path='fourslash.ts' />
+
+// @noImplicitAny: true
+//// function f(new C(100, 3, undefined)
+
+verify.not.codeFixAvailable([]);
+