typecheck

type FunctionShape struct {
	Params     []*Type
	Returns    []*Type
	IsVararg   bool
	VarargType *Type

	// TypeParams names the function's generic parameters (`f<T, U>`). Non-
	// empty for a generic function; call-site inference resolves them.
	TypeParams []string

	// Struct, when non-nil, marks this function as a struct constructor.
	// The checker then also accepts the single-table "named" call form
	// (`Point{ x = 1, y = 2 }`) in addition to the positional Params form.
	// Field is the ordered struct field list used to validate the named
	// form. FieldNames parallels Params for named-arg checking.
	Struct *StructCtor
}

type Indexer struct {
	Key   *Type
	Value *Type
}

type Kind int

type Options struct {
	// Strict: report unannotated function parameters and missing alias
	// resolutions as errors (instead of falling back to `any`).
	Strict bool
}

type StructCtor struct {
	Name  string
	Shape *TableShape
}

type TableField struct {
	Key  string
	Type *Type
}

type TableShape struct {
	Fields  []TableField
	Indexer *Indexer
}

type Type struct {
	Kind Kind

	// Populated by Kind:
	Fn    *FunctionShape // KindFunction
	Table *TableShape    // KindTable
	Union []*Type        // KindUnion (always ≥ 2 members; flattened, deduped)

	// AliasName preserves the user-written alias for diagnostics. Set when
	// resolving a TypeName; the structural Kind/Fn/Table fields are still
	// the source of truth for assignability.
	AliasName string
}

type TypeError struct {
	Line    int
	Code    string // short stable identifier for tooling, e.g. "incompat-assign"
	Message string // human-readable, single-line
	Got     *Type  // optional — populated for assignability errors
	Want    *Type  // optional — populated for assignability errors
}

type TypeErrors struct {
	Errors []TypeError
}