coverage

type ColumnDecl struct {
	// Type is the destination column type, as its DDL spells it.
	Type string `yaml:"type"`

	// Value overrides the key's canonical value. Empty means the canonical
	// one. Only the utf8 row may set it: text is the only thing a destination
	// reparses, and a value declared for any other key would be ignored.
	Value string `yaml:"value"`

	// Expect is what the destination must hold afterwards, as ReadBack renders
	// it. Declared rather than recorded from a run: a table copied from the
	// sink compares the sink to itself.
	Expect string `yaml:"expect"`

	// Instant marks a pair the timestamp claim must exercise with the host
	// clock moved off UTC. It is how a text value bound for a temporal column
	// -- #153's shape, which no Arrow key describes -- reaches that verdict.
	Instant bool `yaml:"instant"`
}

type LatticeEntry struct {
	// Key is conformance.CanonicalKey's output for the type, not
	// DataType.String(): those differ, and only the canonical form matches
	// both what DuckDB emits and what a test constructs.
	Key string `yaml:"key"`

	// DuckDB names the SQL types a user casts to in handler SQL. The rendered
	// integration page is keyed by these, because a user writes a CAST and
	// never sees an Arrow type.
	DuckDB []string `yaml:"duckdb"`

	// Depth is 1 for a scalar, 2 for a container.
	Depth int `yaml:"depth"`
}

type NullRule struct {
	Outcome string `yaml:"outcome"`
	Rule    string `yaml:"rule"`
}

type TypeDecl struct {
	// Key is the lattice.yml key. It is the mapping key in the YAML, so
	// TypesFor fills it in rather than the parser.
	Key string `yaml:"-"`

	// Outcome is exact, coerced or unsupported.
	Outcome string `yaml:"outcome"`

	// Rule states a coercion in prose, for the rendered page. Required when
	// Outcome is coerced: a coercion with no rule is an excuse, and a reader
	// cannot predict what their column will hold.
	Rule string `yaml:"rule"`

	// Code is the errs code an unsupported type must fail with.
	Code string `yaml:"code"`

	// Columns are the destination column types that accept this key, each
	// carrying what to write and what must come back. Every one is exercised,
	// and the cell is covered only when all of them pass.
	//
	// The pair is the unit rather than the key. One Arrow key reaches several
	// destinations that demand different content -- DuckDB's VARCHAR is the
	// universal text carrier, and ClickHouse reparses text into UUID, Decimal
	// and Enum -- so the value belongs here.
	Columns []ColumnDecl `yaml:"columns"`
}