Diagnostics reference

smelt emits named diagnostic codes through its compiler, LSP server, and CLI. Every diagnostic carries a severity level (Error, Warning, Info, Hint), a human-readable message, and a stable code you can use to look up remediation guidance.

Severity levels

Severity	Meaning
Error	The model or function declaration is invalid; smelt will not compile the project until the error is resolved.
Warning	Likely incorrect or sub-optimal; the project compiles but may behave unexpectedly.
Info / Hint	Informational; no action required.

Code catalogue

The complete DiagnosticCode catalogue — every variant, its severity, and the user-input condition that triggers it — is maintained in docs/specs/diagnostics.md. Codes are grouped by owning feature: models & core analysis, sources, seeds, timeseries, incremental & cumulative, types, Python models, functions & expansion, meta-language, records/maps/loaders, and multi-model production.

Example: UnknownStructFieldType

Severity: Error

Emitted when a smelt.define or smelt.extern parameter or return-type annotation contains a Struct<{…}> shape whose field type text cannot be resolved to a recognised DataType. The diagnostic is anchored at the individual field's type-reference span, not the whole annotation, so the exact bad token is highlighted.

Example — the following emits UnknownStructFieldType on the Bogus span:

smelt.define my_fn(t: Expr<Struct<{a: Integer, b: Bogus}>>) -> Expr<Integer> AS (
  t.a
)

Fix: Replace the unrecognised type name with a concrete smelt DataType such as Integer, Text, Float, Boolean, Timestamp, or a nested Struct<{…}>.