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refactor(aura-core): split Scalar into a tag-free Cell + ScalarKind

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Motivation
----------
`Scalar` was a tagged enum (I64/F64/Bool/Ts), so every scalar value
physically carried its own kind tag. But the kind is already known from
the schema/port/column the value flows through (C7: the type is a
property of the column, not of the value — the hot path is already
columnar `Column<T>`, and `AnyColumn::get` *reconstructs* the tag from
the column on the way out). The per-value tag was therefore redundant
with the kind the surrounding context already holds.

That redundancy had three costs:

  * It baked an implicit `match` (a branch) into every function that read
    a Scalar payload — even where the caller statically knew the type.
    The tag could never be exploited away.
  * Size: a tagged enum is tag + payload = 16 bytes (f64/i64 alignment),
    twice the 8 bytes the value needs. A `Column<Scalar>` would be double
    the memory and half the cache utilisation.
  * It is the shared root of several downstream papercuts we keep hitting
    — the lossy f64 manifest field, the `unreachable!` panic on a
    non-numeric param, the serde-tag question — all symptoms of "the type
    is baked into the value".

Change
------
Introduce `Cell`: a type-erased 64-bit word (`struct Cell(u64)`) that is
not readable without external type context. It is constructed per base
type (`from_i64/from_f64/from_bool/from_ts`) and read only by naming the
type at the call site (`i64()/f64()/bool()/ts()`) — each a branch-free
bit-cast. The hot path resolves the kind once at the boundary (from the
schema) and then reads natively, with no per-value branch. `Cell` knows
nothing of `Scalar` or `ScalarKind`; the dependency is strictly one-way,
and it lives in its own `cell.rs` (more is planned on top of it).

`Scalar` becomes `struct { kind: ScalarKind, cell: Cell }` — the
self-describing form for the dynamic boundaries (builder binding,
serialization, rendering), built on top of `Cell`. Its `as_*` accessors
now `debug_assert` the kind and return the native value (free in
release); calling the wrong accessor is a caller bug, not a checked
`Option`. The variant constructors `Scalar::I64(..)` become associated
fns `Scalar::i64(..)`.

`PartialEq` is hand-written (not derived) to preserve the former enum's
value semantics: kinds must match, then native payloads compare, so f64
keeps IEEE-754 behaviour (`NaN != NaN`, `+0.0 == -0.0`) and a kind
mismatch is never equal even when the raw words coincide. A fixture
(`scalar_eq_is_value_not_bitwise`) pins exactly the cases where bit- and
value-equality diverge, so it can't silently regress. `Cell`'s own
`Eq`/`Hash` stay bitwise — correct for a raw word.

The change is behaviour-preserving: Scalar's observable behaviour is
identical to the pre-Cell enum (the value-equality fixture proves it);
only the internal representation changed. The ~440 call sites across the
workspace are a mechanical constructor rename plus ~12 destructuring
sites (match-arms / `let`-patterns) rewritten to `kind()` + `as_*`.

Verified: cargo build --workspace --all-targets, cargo clippy --workspace
--all-targets -- -D warnings, cargo test --workspace — all green.
This commit is contained in:
Brummel
2026-06-16 12:12:52 +02:00
parent b188773fb8
commit cd3d1ca9ed
28 changed files with 573 additions and 429 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/aura-std/src/recorder.rs
+11 -11
View File
@@ -62,10 +62,10 @@ impl Node for Recorder {
for (i, &kind) in self.kinds.iter().enumerate() {
// newest of each column by kind; `?` returns None (warm-up) if cold.
let scalar = match kind {
ScalarKind::F64 => Scalar::F64(ctx.f64_in(i).get(0)?),
ScalarKind::I64 => Scalar::I64(ctx.i64_in(i).get(0)?),
ScalarKind::Bool => Scalar::Bool(ctx.bool_in(i).get(0)?),
ScalarKind::Timestamp => Scalar::Ts(ctx.ts_in(i).get(0)?),
ScalarKind::F64 => Scalar::f64(ctx.f64_in(i).get(0)?),
ScalarKind::I64 => Scalar::i64(ctx.i64_in(i).get(0)?),
ScalarKind::Bool => Scalar::bool(ctx.bool_in(i).get(0)?),
ScalarKind::Timestamp => Scalar::ts(ctx.ts_in(i).get(0)?),
};
row.push(scalar);
}
@@ -107,16 +107,16 @@ mod tests {
// warm: returns None (pure consumer) but records (now, [F64(newest)]).
for (t, v) in [(2_i64, 10.0_f64), (3, 20.0), (4, 30.0)] {
inputs[0].push(Scalar::F64(v)).unwrap();
inputs[0].push(Scalar::f64(v)).unwrap();
assert_eq!(rec.eval(Ctx::new(&inputs, Timestamp(t))), None);
}
let rows: Vec<(Timestamp, Vec<Scalar>)> = rx.try_iter().collect();
assert_eq!(
rows,
vec![
(Timestamp(2), vec![Scalar::F64(10.0)]),
(Timestamp(3), vec![Scalar::F64(20.0)]),
(Timestamp(4), vec![Scalar::F64(30.0)]),
(Timestamp(2), vec![Scalar::f64(10.0)]),
(Timestamp(3), vec![Scalar::f64(20.0)]),
(Timestamp(4), vec![Scalar::f64(30.0)]),
]
);
}
@@ -131,15 +131,15 @@ mod tests {
];
// only column 0 present -> None, nothing recorded.
inputs[0].push(Scalar::F64(1.0)).unwrap();
inputs[0].push(Scalar::f64(1.0)).unwrap();
assert_eq!(rec.eval(Ctx::new(&inputs, Timestamp(1))), None);
assert!(rx.try_recv().is_err());
// both present -> records the full row (still returns None).
inputs[1].push(Scalar::F64(2.0)).unwrap();
inputs[1].push(Scalar::f64(2.0)).unwrap();
assert_eq!(rec.eval(Ctx::new(&inputs, Timestamp(2))), None);
let rows: Vec<(Timestamp, Vec<Scalar>)> = rx.try_iter().collect();
assert_eq!(rows, vec![(Timestamp(2), vec![Scalar::F64(1.0), Scalar::F64(2.0)])]);
assert_eq!(rows, vec![(Timestamp(2), vec![Scalar::f64(1.0), Scalar::f64(2.0)])]);
}
#[test]