Generic cells in doppel

[mkeeter]

(staged on #662)

This PR makes cell types in doppel generic, then uses that new functionality where relevant.

It requires editing the proc macro to support generic parameters, but then can remove the explicit impl Load for MaybeUninit<T> implementation.

[Copilot]

Pull request overview

This PR updates the Load derive proc-macro and the humility_doppel “cell” mirror types to support typed/generic cells (e.g., StaticCell<Ringbuf>), then updates call sites to use the new typed cells and simplify value extraction.

Changes:

• Extend #[derive(Load)] code generation to include generic parameters for derived struct impls.
• Make doppel cell wrapper types (ClaimOnceCell, StaticCell, UnsafeCell, MaybeUninit) generic over the loaded payload type and remove the bespoke Load impl for MaybeUninit<T>.
• Update host, ringbuf, and spd to use typed cell reads (via reflect::read_variable) and avoid redundant from_value calls.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
load_derive/src/lib.rs	Adds helper functions to emit generics in generated impl Load blocks for derived structs.
humility-doppel/src/lib.rs	Makes cell wrapper types generic and switches MaybeUninit<T> to #[derive(Load)] instead of a manual impl.
humility-spd/src/lib.rs	Uses typed ClaimOnceCell<reflect::Struct> loading to simplify packrat buffer handling and removes manual loading steps.
cmd/ringbuf/src/lib.rs	Uses StaticCell<Ringbuf> to avoid re-parsing the ringbuf after unwrapping the cell.
cmd/host/src/lib.rs	Uses ClaimOnceCell<HostStateBuf> and returns the typed inner value directly.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mkeeter]

Tested on gimlet-d:

matt@niles ~ () $ pfexec ./humility -t gimlet-d host boot-fail
humility: attached to 0483:3754:000D00344741500820383733 via ST-Link V3
Message contains no non-NUL bytes, not printing.
matt@niles ~ () $ pfexec ./humility -t gimlet-d spd
humility: attached to 0483:3754:000D00344741500820383733 via ST-Link V3
ADDR MANUFACTURER              PART                 WEEK YEAR
   0 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   1 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   2 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   3 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   4 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   5 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   6 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   7 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   8 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
   9 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
  10 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
  11 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
  12 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
  13 Micron Technology         36ASF8G72PZ-3G2E1      34 2022
  14 Micron Technology         36ASF8G72PZ-3G2F1       2 2023
  15 Micron Technology         36ASF8G72PZ-3G2F1       2 2023