guarantee that $page.route has the correct shape

[Rich-Harris]

fixes #8351. This bug was made possible by lazy typing, so rather than add a new test (since we really need to figure out a way to reduce our reliance on e2e tests) I made the types stricter instead.

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[Conduitry]

Is this the shape we want? To me this seems a little bit similar to the event.platform issue where it was decided that event.platform itself could be undefined, not an empty object. What's the justification for saying that event.platform might be undefined but page.route isn't?

[Rich-Harris]

page.route is always defined, but sometimes its id is null

[Rich-Harris]

ah wait, I understand what you're saying. err... i don't recall the justification for this, but i do remember us discussing it and landing on this

[Conduitry]

That's fine, I just wanted to bring this up. I'll trust your memory of some previous discussions about this.

[dummdidumm]

We did discuss it and one of the reasons we landed on it was that writing route?.id instead of route.id (and therefore crashing at runtime sometimes) is probably an easy mistake to make.

[Rich-Harris]

cool, will go ahead and merge this