Merge pull request #21744 from Microsoft/fixGetConstrainedTypeParameter

Fix getConstrainedTypeParameter function

src/compiler/checker.ts

@@ -7245,7 +7245,7 @@ namespace ts {
 
         function getConstrainedTypeParameter(typeParameter: TypeParameter, node: Node) {
             let constraints: Type[];
-            while (isTypeNode(node)) {
+            while (isPartOfTypeNode(node)) {
                 const parent = node.parent;
                 if (parent.kind === SyntaxKind.ConditionalType && node === (<ConditionalTypeNode>parent).trueType) {
                     if (getTypeFromTypeNode((<ConditionalTypeNode>parent).checkType) === typeParameter) {

src/compiler/utilities.ts

@@ -771,6 +771,8 @@ namespace ts {
                 return node.parent.kind !== SyntaxKind.VoidExpression;
             case SyntaxKind.ExpressionWithTypeArguments:
                 return !isExpressionWithTypeArgumentsInClassExtendsClause(node);
+            case SyntaxKind.TypeParameter:
+                return node.parent.kind === SyntaxKind.MappedType || node.parent.kind === SyntaxKind.InferType;
 
             // Identifiers and qualified names may be type nodes, depending on their context. Climb
             // above them to find the lowest container