Module registry 

Declarative metric registry — the data-driven home for tier-2+ formulas.

A MetricDef pairs a CEL formula_cel with its spec (label / direction / …). The default registry ships built-in derived metrics; a user adds their own by editing config (e.g. comment_ratio = "sloc > 0.0 ? cloc / sloc * 100.0 : 0.0"). The Engine compiles each formula once, topologically orders them by inter-metric dependencies, and evaluates them per node over the node’s numeric attributes — the same engine will serve file and function units.

Scope: today the engine evaluates node-scope metrics and is used to compute extra metrics on top of the built-in Rust derivation, so the default pipeline (and its goldens) are untouched until this is wired in. Graph-scope aggregates (scope = graph, percentiles, reducers) come later.

Structs

Engine

A compiled, topologically ordered set of metric programs, split by scope: node-scope (per node) and graph-scope (once over the whole node set, via the agg(key, reducer, population) reducer function).

MetricDef

One metric definition: a CEL formula plus the spec fields needed to emit it as a first-class, sortable, delta-coloured attribute. Spec fields are optional so a quick user formula needs only formula_cel.

Populations

The value populations an aggregate reduces over, per metric key. Two flavours per the metric’s no-signal value (omit_at):

Enums

RegistryError

Errors surfaced when loading/compiling a registry — all caught at load time (not per node), so a bad user formula fails fast with a clear message.

Scope

Where a metric is evaluated: per node (default) or once over a collection.

Functions

apply_to_node

Apply the node-scope engine to one node: read its numeric attributes, compute every registry metric, and write the results back, omitting each at its omit_at exactly like crate::write_metrics. Built-in attributes already present are used as inputs.