It looks like the list of imports provided by getSourceFile, ultimately used by getReferencedFiles, includes a tslib import, which seems reasonable.

However, the parent of the importName is Program itself, which does not have a parent. getSymbolAtLocation on the tslib import will, internally, call isExternalModuleImportEqualsDeclaration on the node.parent.parent, which doesn't exist, leading to a crash.

This prevents IntelliSense in VS Code from working at all.

A local hack that, because it was easy, I have implemented is wrapping the checker.getSymbolAtLocation call in Project.prototype.getReferencedFiles in a try/catch block that rethrows the exception unless importName.text === 'tslib'. This restores IntelliSense to working condition.

Including any tslib helper (by way of importHelpers) is enough to cause the crash.

async function x() {}