`zerodds-flatdata-derive`

Proc-macro #[derive(FlatStruct)] for the zerodds-flatdata trait. Generates unsafe impl FlatStruct for T with a deterministic SHA-256-based TYPE_HASH derived from the type name and field layout. Safety classification: STANDARD (proc-macro).

Spec mapping

Spec	Section
ZeroDDS-flatdata 1.0	§1.2 (derive macro)

What's inside

#[derive(FlatStruct)] — generates unsafe impl ::zerodds_flatdata::FlatStruct with TYPE_HASH = sha256(layout_signature(T))[..16].
Compile-time checks:
- enum/union are rejected with compile_error! (no stable layout).
- A missing #[repr(C)] / #[repr(transparent)] is rejected with compile_error! (the default repr is not guaranteed to be layout-stable).
Layout signature <TypeName>{<field-name>:<field-ty>,...} detects type rename, field add/remove, field reorder, field type change.

Layer position

Layer 4 — Core Services. Build-time companion to zerodds-flatdata, no runtime code surface. No ZeroDDS crate deps.

Quickstart

use zerodds_flatdata_derive::FlatStruct;

#[derive(Copy, Clone, FlatStruct)]
#[repr(C)]
struct Pose { x: f64, y: f64, z: f64 }

// expandiert zu:
//
//   unsafe impl ::zerodds_flatdata::FlatStruct for Pose {
//       const TYPE_HASH: [u8; 16] = [/* sha256("Pose{x:f64,y:f64,z:f64}")[..16] */];
//   }

WIRE_SIZE and the as_bytes/from_bytes_unchecked methods come as a default from the trait and need no macro override.

Feature flags

None. The crate is a pure proc-macro lib.

Stability

1.0.0-rc.1 is the initial release materialization. All public macro paths are RC1-stable; the layout signature format is considered wire-stable — a change would invalidate all generated TYPE_HASH values and is therefore major-breaking.

Build & Test

cargo build -p zerodds-flatdata-derive
# Tests live in zerodds-flatdata because proc-macro crates cannot test
# their own output:
cargo test -p zerodds-flatdata --test derive

License

Apache-2.0. See LICENSE.

zerodds-flatdata-derive 1.0.0-rc.5