LDC-E1402 — Requirement on an unknown feature

What it means

A declaration can require a language feature: without that feature, the declaration must not be read as written. The annotation names the feature, and the name must come from the feature registry — an unknown name cannot be allowed through as informational, because a misspelled requirement would silently stop constraining. The compiler stops at the annotation and lists the features it knows.

The repair is to name a registered feature, or to drop the requirement. A requirement on a feature nobody registered constrains nothing.

Example

Arxo Law

language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

@requires_feature("nope.nothing")
entity A;

Fix

Arxo Law

language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

entity A;

Engine message

The engine reports this in its own wording:

Output

example.law:5:1: error LDC-E1402: feature "nope.nothing" is absent from the registry (§26): an unknown gate cannot be treated as informational — known: law.cert/0.1, law.cnl/0.1, law.decision/0.1, law.deontic/0.1, law.evidence_policy/0.1, law.layers/0.1, law.params/0.1, law.precedent/0.2, law.review/0.1, law.units/0.1, law.verb/0.1, law.verb/0.2

Related

• LDC-E1403 — a requirement on a reserved feature.
• LDC-E1401 — a language line the engine does not support.