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Diagnostics

Diagnostics are span-tracked, severity-tagged messages with a stable SDxxxx code. They live in crates/mty-diagnostics/.

Types

pub enum Severity { Error, Warning, Note, Help }

pub struct Label {
    pub start: usize,
    pub end: usize,
    pub message: String,
}

pub struct Diagnostic {
    pub code: DiagCode,
    pub severity: Severity,
    pub primary: Label,
    pub secondary: Vec<Label>,
    pub notes: Vec<String>,
    pub helps: Vec<String>,
}

The builder pattern:

Diagnostic::error(codes::EXPECTED_ITEM, primary_label)
    .with_note("agents must be declared at top level")
    .with_help("did you mean to wrap this in `fn main`?")
    .with_secondary(other_label);

Codes

DiagCode(pub u16) with a formatted as_str() of SD{:04}. All codes are defined as pub const in codes.rs. Once assigned, a code is never renumbered.

See the diagnostic registry for the canonical table.

Rendering

render::ariadne::render(&diagnostic, source_id, source) -> String
render::ariadne::render_all(&diagnostics, source_id, source) -> String

The renderer wraps ariadne and produces a colorized (when stderr is a TTY), span-highlighted report. Severity maps to ariadne's ReportKind; primary labels render red, secondary yellow.

Producing diagnostics

Two main pathways:

  1. Parser errors — Parser::error_at(message, start, end) records a ParseError. The driver converts these into Diagnostic values with code UNEXPECTED_TOKEN (MT0001).
  2. HIR lowering — LoweringCtx.diagnostics: Vec<Diagnostic> is pushed to directly by lowering submodules with the appropriate SD1xxx code.

The driver merges both lists into the final diagnostics returned to the CLI.

Future

  • Source-mapped JSON output for editor / LSP integration.
  • Severity policy per profile (warnings-as-errors in strict mode).
  • Suggested-edit metadata so mty fmt can apply auto-fixes.