| name | masm-rust-constant-parity |
| description | Use when changing a numeric or string constant in Rust or MASM that has a counterpart on the other side — keep the two definitions from drifting apart. |
Keep Rust and MASM Constants Aligned
Rule
Constants that exist on both the MASM and the Rust side must not drift. Prefer a single source of truth: define the constant in MASM and generate the Rust counterpart from it, rather than hand-maintaining the same literal in two places.
This repo already does that in crates/miden-protocol/build.rs: it scans the MASM sources for const ERR_... = "..." and const X = event("...") definitions and emits Rust files (tx_kernel_errors.rs, protocol_errors.rs, transaction_events.rs) that are pulled in with include!(concat!(env!("OUT_DIR"), ...)) (see src/errors/mod.rs and src/transaction/kernel/tx_event_id.rs). A new error or event constant added in MASM gets its Rust binding automatically.
For constants not covered by codegen (memory offsets, capacity limits, field widths still duplicated in src/constants.rs and src/transaction/kernel/memory.rs, mirroring asm/kernels/transaction/lib/memory.masm), update both sides in the same PR — and prefer extending the generation over adding another hand-copied literal.
Why
The kernel reads memory at offsets the Rust host wrote. If one side changes ACTIVE_INPUT_NOTE_PTR and the other doesn't, every transaction misreads its state, and the bug stays invisible until a value happens to straddle the changed offset. Generating one side from the other removes the chance to forget.
Examples
Source of truth in MASM:
const ERR_PROLOGUE_NEW_ACCOUNT_VAULT_MUST_BE_EMPTY="new account must have an empty vault"
Generated into OUT_DIR by build.rs and included via include!(concat!(env!("OUT_DIR"), "/tx_kernel_errors.rs")):
pub const ERR_PROLOGUE_NEW_ACCOUNT_VAULT_MUST_BE_EMPTY: MasmError =
MasmError::from_static_str("new account must have an empty vault");
For a constant that is still hand-duplicated, change both in the same PR:
pub const MAX_INPUT_NOTES_PER_TX: usize = 1024;
# crates/miden-protocol/asm/kernels/transaction/lib/constants.masm — must equal the Rust constant
pub const MAX_INPUT_NOTES_PER_TX = 1024
