Remove usage of method placeholder functions

[devennavani]

This PR introduces a new minor client version 0.67.x that does not create method placeholder functions for modal classes.

I've tested all forward lookup scenarios (.lookup() of a 0.67 class from a pre 0.67 client) as well as backwards lookup scenarios (.lookup() of a pre 0.67 class from a 0.67 client) and all work, except for a 0.62 client looking up a 0.67 class, which will be explicitly not supported (this maintains our current restriction of not being able to lookup a 0.63+ class from a 0.62 client).

Changelog

New minor client version 0.67.x comes with an internal data model change for how Modal creates functions for Modal classes. There are no breaking or backwards-incompatible changes with this new minor version. All forward lookup scenarios (.lookup() of a 0.67 class from a pre 0.67 client) as well as backwards lookup scenarios (.lookup() of a pre 0.67 class from a 0.67 client) work, except for a 0.62 client looking up a 0.67 class (this maintains our current restriction of not being able to lookup a 0.63+ class from a 0.62 client).

[freider]

lovely! did we decide to not backfill method metadata on existing classes in order to remove existing placeholders? (completely understandable, seems messy).

Another related question:
Will "forward" lookups work after this? I.e. can a 0.63 client .lookup() a 0.67 class? The way I understand the ClassGet backend implementation the answer is yes, since it "mocks out" placeholders with the function id set to the class service function?

[devennavani]

lovely! did we decide to not backfill method metadata on existing classes in order to remove existing placeholders? (completely understandable, seems messy).

Another related question: Will "forward" lookups work after this? I.e. can a 0.63 client .lookup() a 0.67 class? The way I understand the ClassGet backend implementation the answer is yes, since it "mocks out" placeholders with the function id set to the class service function?

@freider yes, forward lookups will work, excluding lookups from a 0.62 client, which is currently not supported either.

re: your first question, yea it feels a bit messy. i'm guessing i would have to have the server modify the class service function definitions coming from older clients to include the method definitions mapping and that will likely introduce more confusion

[devennavani]

@prbot approve

[modal-pr-review-automation]

Approved 👍. @mwaskom will follow-up review this.

[mwaskom]

I know this mostly involves internal changes but is there anything we should put in a public changelog here? Users will see the version bump and wonder what's non-compatible.

I left a few other comments but mostly Python trivia that you don't need to address.

This change is touching some very complicated stuff and I didn't fully pore through all the details, as I trust you've exercised it thoroughly in your testing. LMK if you'd feel more comfortable with me doing that before you merge.