Cherry-pick PR #46614 into release-4.5 (#46675)

Component commits: e77514a Add failing test. 3c0d51b Check for type parameters on the original type when asking for the type argument constraint. e7c8095 Update tests/cases/fourslash/stringLiteralTypeCompletionsInTypeArgForNonGeneric1.ts Co-authored-by: Daniel Rosenwasser <[email protected]>
microsoft · Nov 3, 2021 · 0651bd3 · 0651bd3
1 parent e4a2494
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diff --git 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
@@ -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() });
+