From 0651bd3adaa814d494528d7a004054f825cb8a38 Mon Sep 17 00:00:00 2001
From: TypeScript Bot <ts_bot@rcavanaugh.com>
Date: Wed, 3 Nov 2021 15:07:23 -0700
Subject: [PATCH] Cherry-pick PR #46614 into release-4.5 (#46675)

Component commits:
e77514a53b Add failing test.

3c0d51b3ed Check for type parameters on the original type when asking for the type argument constraint.

e7c8095935 Update tests/cases/fourslash/stringLiteralTypeCompletionsInTypeArgForNonGeneric1.ts

Co-authored-by: Daniel Rosenwasser <drosen@microsoft.com>
---
 src/compiler/checker.ts                                |  3 ++-
 ...ingLiteralTypeCompletionsInTypeArgForNonGeneric1.ts | 10 ++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 tests/cases/fourslash/stringLiteralTypeCompletionsInTypeArgForNonGeneric1.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 9d1bf23546c..2e051e97740 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -34730,7 +34730,8 @@ namespace ts {
         function getTypeArgumentConstraint(node: TypeNode): Type | undefined {
             const typeReferenceNode = tryCast(node.parent, isTypeReferenceType);
             if (!typeReferenceNode) return undefined;
-            const typeParameters = getTypeParametersForTypeReference(typeReferenceNode)!; // TODO: GH#18217
+            const typeParameters = getTypeParametersForTypeReference(typeReferenceNode);
+            if (!typeParameters) return undefined;
             const constraint = getConstraintOfTypeParameter(typeParameters[typeReferenceNode.typeArguments!.indexOf(node)]);
             return constraint && instantiateType(constraint, createTypeMapper(typeParameters, getEffectiveTypeArguments(typeReferenceNode, typeParameters)));
         }
diff --git a/tests/cases/fourslash/stringLiteralTypeCompletionsInTypeArgForNonGeneric1.ts b/tests/cases/fourslash/stringLiteralTypeCompletionsInTypeArgForNonGeneric1.ts
new file mode 100644
index 00000000000..7c1a11889a6
--- /dev/null
+++ b/tests/cases/fourslash/stringLiteralTypeCompletionsInTypeArgForNonGeneric1.ts
@@ -0,0 +1,10 @@
+/// <reference path="./fourslash.ts" />
+
+////interface Foo {}
+////type Bar = {};
+////
+////let x: Foo<"/*1*/">;
+////let y: Bar<"/*2*/">;
+
+verify.completions({ marker: test.markers() });
+