Appendix C — Diagnostic Codes

Argon diagnostics use a structured naming scheme: OE / OW / OI plus four digits. Run ox explain <code> for the long-form explanation of any diagnostic.

The naming scheme:

OE (Oxide Error) — the build fails. Codes in the four-digit range; the leading two digits categorise the source area (compiler / runtime / package / kernel / network / …).
OW (Oxide Warning) — the build proceeds; the issue is flagged.
OI (Oxide Info) — informational hint; nothing is wrong.

ox explain <code> prints the canonical long-form explanation and a fix suggestion. The reference below lists every code shipped today, organised by category.

Parser (`OE0001`–`OE0004`)

Code	Meaning
`OE0001`	Unexpected token
`OE0002`	Unclosed block
`OE0003`	Invalid decorator syntax
`OE0004`	Invalid character in identifier

Resolution (`OE0101`–`OE0103`)

Code	Meaning
`OE0101`	Unresolved name
`OE0102`	Ambiguous import
`OE0103`	Cyclic module dependency

Type system + meta-property structural rules (`OE/OW/OI 02xx`)

Code	Meaning
`OE0201`	Concept used as relation, or vice versa
`OE0202`	Property type mismatch
`OE0203`	Non-exhaustive `match` or cardinality violation
`OE0204`	Rigid type specializing anti-rigid type
`OE0205`	Role used as concept
`OE0206`	Duplicate declaration
`OE0207`	Mixed-strength rules on same head
`OE0208`	`compute` call arg-count mismatch
`OE0210`	Recursive `compute`-call cycle
`OE0211`	`derive` head’s consequence atoms cannot lower (silent rule drop refused)
`OE0212`	`meta(X)` argument is not ground at rule time
`OE0213`	`expect { diagnostic <code> }` references an unknown diagnostic code
`OE0214`	`using <name>` clause on `test` references an unresolved frame
`OE0215`	Two composed frames declare the same-named member
`OE0216`	Inline `fixture` redeclares a frame member
`OE0218`	Frame include chain forms a cycle
`OE0219`	Rule-body aggregate cannot be lowered into the Datalog body
`OE0221`	Relation cardinality has `min > max` (unsatisfiable range)
`OE0222`	`let _ as <handle>: T` shadows a binding in the enclosing scope
`OE0223`	Anonymous-type content-hash collision (defensive; astronomically rare)
`OW0207`	Sortal missing `Kind` ancestor (UFO structural R28)
`OW0208`	Anti-rigid under `Category` without `Kind` in path (R24)
`OW0209`	Mixin lacks rigid or anti-rigid subtypes (R25)
`OW0210`	Non-sortal aggregates only one `Kind` (R30–R31)
`OW0211`	Role has no mediation path to relator (R34)
`OW0212`	Phase has no sibling phase (R35)
`OW0213`	Phase / phasemixin cross-specialization (R32–R33)
`OW0214`	Phasemixin has no `Category` ancestor (R36)
`OW0215`	`@requires` / `@requires_all` deprecated; use `where` clause
`OI0216`	`box()` tautology — rigid type necessarily satisfies
`OE0217`	`box()` impossible — anti-rigid cannot satisfy necessity
`OI0218`	`diamond()` tautology — anti-rigid trivially possible
`OW0219`	`kind` specializes `kind` — consider `subkind`
`OE0220`	Inner doc comment not at module scope
`OE0224`	Test assertion arity mismatch (`assert Concept(individual)` vs `assert role(subj, obj)`)

Metatype substrate (`OE 022x`–`023x`)

User-declared metaxis / metatype / metarel / decorator declarations and their application sites.

Code	Meaning
`OE0225`	Unknown `metarel` — application or path resolution to a nonexistent metarel
`OE0226`	`pub rel` endpoints don’t satisfy the bridging metarel’s `source` / `target` constraints
`OE0227`	`metaxis for <kind>` qualifier names an unknown declaration kind, or a metaxis is used in a metarel context (or vice versa)
`OE0228`	`metaxis <Name> { … }` lacks the required `for <kind>` qualifier
`OE0229`	`@[<name>]` does not resolve to a `pub decorator`
`OE0230`	Decorator application argument count doesn’t match declared parameter count
`OE0231`	Decorator’s `on <Target>` doesn’t match the application site
`OE0232`	`lowers_to: <hint>` clause names a recognizer shape that doesn’t pattern-match the body
`OE0233`	Decorator’s explicit `fragment: <tier>` contradicts the inferred body tier
`OE0234`	Decorator argument value doesn’t satisfy the parameter type
`OE0235`	`compute` has no body and no `impl rust(...)` binding

Collections (`OE/OW 24xx`)

Diagnostics for the collection substrate covered in Chapter 2.8.

Code	Meaning
`OE2401`	Type-constructor arity mismatch — `Set[T, U]`, `Map[T]`, `Optional[T, U]`. `Set` / `List` / `Optional` / `Range` take 1 type argument; `Map` takes 2.
`OE2402`	Collection-op expression form parsed cleanly but full UFCS desugaring and runtime evaluation are not yet wired (tracked by the E3 epic). Workaround: write the qualified-call form (`std::collection::List::size(xs)`) or rebuild via direct field assignments.
`OE2403`	Collection element-type mismatch — `List[Nat].append("foo")`, `[1, "two", true]`. Argon collections are homogeneous; the expected element type comes from the receiver’s declared type.
`OE2404`	Index expression’s type isn’t `Nat` (for `List`) or doesn’t match the declared key type (for `Map::get`).
`OE2405`	Slice bounds invalid — `xs[5..2]`, negative literal bound. Checked at elaboration for literal bounds; dynamic bounds are checked at runtime.
`OE2406`	Unordered collection indexed — `s[i]` where `s: Set[T]`. Set elements have no positional identity; use `Set::contains` for membership tests or convert to a `List`.
`OE2407`	Higher-order argument’s signature does not match the operation’s expected closure shape (`xs.map(f)` where `f` has the wrong arity or wrong argument types).
`OE2408`	Higher-tier collection op used inside a context that admits only `tier:closure` or below — typically `xs.map(f)` inside a `derive` rule body. Lift the transformation into a `pub compute` or rewrite using closure-tier ops.
`OW2401`	`Optional` unwrapped without a clear fallback — bare `.unwrap()` or `.unwrap_or` whose fallback is itself `Optional[T]`. Provide a concrete `T`-typed fallback or guard with `is_some`.
`OW2402`	`[T; <= 1]` is a singleton-bounded set; `Optional[T]` (sugared `T?`) expresses the same intent more directly and integrates with the `Optional` op surface. Quickfix suggestion, not a hard error.
`OW2403`	Comprehension binder shadows a `let` binding or parameter in the enclosing scope. Rename the binder to silence. Matches the fresh-binder convention Datalog rule bodies already use.

Reasoning / DL (`OE/OW 03xx`)

Code	Meaning
`OE0301`	Unsatisfiable concept (TBox-level: contradictory axioms make the concept impossible to instantiate)
`OW0302`	Redundant axiom
`OW0303`	Decidability warning
`OE0304`	Incoherent TBox
`OW0305`	Unsatisfiable concept (warning-severity twin of `OE0301`; what `ox check --reason` actually emits when reasoning over imported / under-specified ontologies, so contradictions in the source don’t gate the check)
`OE0306`	Disjointness violation — ABox contradiction at evaluation time (an individual is asserted as instance of two disjoint concepts; distinct from `OE0301` which is a TBox contradiction)
`OW0307`	Hypothetical block evaluation error — override target shape, missing individual, missing property, or unsupported value type

Defeasibility (`OE 04xx`)

Code	Meaning
`OE0401`	Ambiguous defeat
`OE0402`	Unreachable defeater
`OE0403`	Circular superiority relation

Stratification (`OE 05xx`)

Code	Meaning
`OE0501`	Circular negation
`OE0502`	Unstratifiable program

Constraint (`OE 06xx`)

Code	Meaning
`OE0601`	Unsatisfiable constraint
`OE0603`	`metatype` literal type doesn’t match the axis’s declared `value_type`
`OE0604`	`#dec(<tier>)` enforcement: declaration’s required tier exceeds ambient
`OE0605`	Unknown metatype name (four-variant hint: not-a-metatype-but-found / available-not-imported / multi-package-available / not-declared)
`OE0606`	`metaxis <name> : <T> where { <pred> }` refinement violated by a typed-axis literal

Package / module (`OE 07xx`)

Code	Meaning
`OE0701`	Private concept in public context
`OE0702`	Orphan axiom without `extend` block
`OE0703`	Private item imported across module boundary
`OE0704`	Conflicting explicit imports of the same name
`OE0705`	Ambiguous glob imports at use site
`OE0706`	Import conflicts with local declaration
`OE0707`	Package is not a direct dependency

Decidability tiers (`OE/OW/OI 08xx`)

Code	Meaning
`OI0801`	Non-polynomial reasoning (informational)
`OE0802`	Variable-binding quantifier outside `unsafe` block
`OW0803`	Bounded FOL rule without scope annotation
`OI0804`	Derive-rule decidability classification
`OE0805`	Asserted complexity contradicts classified tier
`OW0806`	Tier-6 rule without heartbeat budget
`OE0807`	Monotone assertion violated by non-monotone atoms
`OI0808`	`unsafe logic` rule gated
`OE0809`	Tier-6 rule outside `unsafe logic` block
`OE0810`	Invalid key in `@[budget]` annotation
`OE0811`	Invalid key in `@[scope]` annotation
`OE0812`	Unknown complexity class
`OW0813`	Deprecated `.ol` extension; rename to `.ar`
`OW0821`	`@[theorem]` applied to a non-derive item
`OW0822`	`@[theorem]` declared multiple times on the same derive
`OW0823`	`#[unproven]` / `#[assumed]` applied to a non-test item

External format warnings (`XW 08xx`)

Code	Meaning
`XW0841`	Unknown OntoUML stereotype preserved as metadata
`XW0842`	OntoUML element name disambiguated on import
`XW0843`	OntoUML aggregation preserved as metadata
`XW0844`	OntoUML relation arity reduced to binary
`XW0845`	OntoUML cardinality letter-shorthand (`n`/`m`) preserved as marker for byte-stable round-trip (Argon’s grammar fully expresses the semantics; the marker only pins the source’s lexical form)
`XW0846`	OntoUML `GeneralizationSet` emitted as Argon structural block (`partition` / `disjoint` / `complete`)
`XW0847`	OntoUML `restrictedTo` natures preserved as metadata
`XW0850`	OntoUML class resolved against registry foundation package (informational; local declaration dropped, `use <pkg>::*` emitted)
`XW0851`	OntoUML source-package collapsed to root because slug matches registry

Export / re-export (`OE 09xx`)

Code	Meaning
`OE0901`	Cannot export private symbol
`OE0902`	Cannot re-export private item
`OE0903`	Re-export cycle detected
`OE0904`	Implicit-head `derive` shadows a declared concept

Reasoning runtime (`RW 00xx`)

Runtime-side diagnostics emitted by the reasoning engine when atom evaluation cannot proceed.

Code	Meaning
`RW0001`	Atom references an unbound variable
`RW0002`	Predicate name resolves to neither a concept, registered compute, nor a derive-rule head
`RW0003`	Atom argument type doesn’t match the resolved predicate’s declared arity / type

Perspectival composition — modules, standpoints, defeat order (`OE/OW 10xx`)

Code	Meaning
`OE1001`	Cyclic standpoint dependency
`OE1002`	Unknown defeat-ordering strategy
`OE1003`	Unknown configuration strategy
`OE1004`	Module references undeclared standpoint
`OE1005`	Duplicate module name
`OW1006`	`extend` block breaks conservative extension
`OE1007`	Cross-module superiority cycle
`OW1008`	CWA concept in OWA module
`OW1009`	Standpoint DAG has no root
`OE1010`	Bridge rule references private concept
`OE1011`	Module discriminator collision
`OW1012`	Tree-shaking excluded a required module
`OE1013`	Unresolvable cross-module defeat target

Diagrams (`OE/OW 11xx`)

Code	Meaning
`OE1101`	Unknown concept in diagram
`OE1102`	Unknown relation in diagram
`OE1103`	Unknown module in diagram
`OE1104`	Concept not accessible in diagram (missing `use`)
`OE1110`	Unknown filter property in diagram predicate
`OE1111`	Type mismatch in diagram predicate
`OE1112`	Non-enumerable property in `color by`
`OE1120`	Concept not in diagram selection
`OE1121`	Contradictory layout constraints
`OE1122`	Concept is both included and excluded in the same diagram
`OE1123`	Concept belongs to two named groups in the same diagram
`OE1124`	`collapse` target is excluded from the diagram
`OW1130`	Empty diagram
`OE1131`	Unknown base diagram in `from` clause
`OE1132`	Unknown named selection

Code	Meaning
`OI1201`	Redundant check — already narrowed by prior atom

Query / mutation / compute (`OE 14xx`)

Code	Meaning
`OE1401`	Mutation `require` clause contains a side-effect expression
`OE1402`	`retract` pattern statically matches multiple assertions
`OE1403`	Mutation return type does not match declared return type
`OE1404`	Query output shape does not match return-type annotation
`OE1405`	Construct exceeds module `max_tier` cap
`OE1406`	Inline-compute body references an unresolved name
`OE1407`	Mutation precondition evaluates to non-`Bool`
`OE1408`	Invalid `@[cached]` placement
`OE1409`	Query head references an unbound variable
`OE1410`	Object literal missing required field
`OE1411`	Object literal has unknown field
`OE1412`	`emit` event type is not a sortal
`OE1413`	Inline-compute result type does not match `out { T }`
`OE1414`	`let` type is non-instantiable (non-sortal mixin)
`OE1415`	List literal in non-collection-field position

Metatype (`OE 15xx`)

Code	Meaning
`OE1501`	Unresolved metatype name

Inline-compute runtime (`OE 17xx`)

Code	Meaning
`OE1700`	Type mismatch in compute body
`OE1701`	Arithmetic error in compute body
`OE1702`	Missing required compute input
`OE1703`	Compute budget exhausted
`OE1704`	Compute scope exceeded
`OE1705`	Body `max_tier` exceeds module cap
`OE1706`	Compute path could not be resolved
`OE1707`	Compute variable not bound
`OE1708`	Unknown predicate in compute body
`OE1709`	Postcondition failed

Lifecycle (`OE/OW 18xx`)

Code	Meaning
`OE1801`	Lifecycle declares transitions but has no `initial` phase
`OE1802`	Lifecycle declares more than one `initial` phase
`OW1803`	Lifecycle has no `terminal` phase
`OW1804`	Lifecycle phase is unreachable from any initial phase
`OW1805`	Lifecycle phase has no path to any terminal phase
`OE1806`	Duplicate phase name in a `lifecycle { … }` block
`OE1807`	Transition references an unknown phase name
`OW1808`	Lifecycle phase data fields not yet elaborated (placeholder)

Looking up a code

$ ox explain OE0204

The full explanation includes the rule violated, a typical example that triggers it, and the canonical fix. ox explain is the authoritative surface — this appendix is a navigation aid, not a replacement.

The Argon Programming Language