Long (infinite?) compile times intersecting with large union

TypeScript Version: 2.7.0-dev.20171108

Code

At the bottom of src/compiler/utilities.ts replace the return type of hasJSDocNodes with:

export function hasJSDocNodes(node: Node): node is HasJSDoc & { jsdoc: JSDoc[] } {

(Since hasJSDocNodes ensures that jsdoc will be defined.)

Expected behavior:

Eventually compiles.

Actual behavior:

Very long compile time. Probably has to do with HasJSDoc being a large union.

As of #22701 there would also be long compile times if properly typing isFromObjectTypeDeclaration at the end of completions.ts. It even seems to happen with just node is Node & { parent: ClassElement | TypeElement }, even though Node isn't a union.