title: Typescript transformer, `node.parent` is undefined
body: <p>I'm currently using a typescript transformer api, and I found that the <code>node.parent</code> is undefined.</p>
  <p>My code is:</p>
  <pre><code>        const transformerFactory: ts.TransformerFactory&lt;ts.Node&gt; = (
              context: ts.TransformationContext
          ) =&gt; {
              return (rootNode) =&gt; {
                  function visit(node: ts.Node): ts.Node {
                      node = ts.visitEachChild(node, visit, context);
  
                      // HERE node.parent IS UNDEFINED !
  
                      return filterFn(node, context);
  
  
                  }
          
                  return ts.visitNode(rootNode, visit);
              };
          };
          
          const transformationResult = ts.transform(
              sourceFile, [transformerFactory]
          );
  </code></pre>
  <p>How can I find the parent of the node?</p>