Can't implement FunctionProvider

time_funcs.go

package sql

import (
	"context"
	"time"

	mysql "github.com/dolthub/go-mysql-server/sql"
	"github.com/dolthub/go-mysql-server/sql/types"
)

type timeRangeKey struct{}

type TimeRange struct {
	From time.Time
	To   time.Time
}

func WithTimeRange(ctx context.Context, from, to time.Time) context.Context {
	return context.WithValue(ctx, timeRangeKey{}, TimeRange{From: from, To: to})
}

func GetTimeRange(ctx context.Context) (TimeRange, bool) {
	tr, ok := ctx.Value(timeRangeKey{}).(TimeRange)
	return tr, ok
	
}

//
// Expressions for time_from() and time_to()
//

type TimeFromExpr struct{}

func (e *TimeFromExpr) Resolved() bool               { return true }
func (e *TimeFromExpr) IsNullable() bool             { return false }
func (e *TimeFromExpr) Children() []mysql.Expression { return nil }
func (e *TimeFromExpr) WithChildren(...mysql.Expression) (mysql.Expression, error) {
	return e, nil
}
func (e *TimeFromExpr) String() string   { return "time_from()" }
func (e *TimeFromExpr) Type() mysql.Type { return types.Timestamp }
func (e *TimeFromExpr) Eval(ctx *mysql.Context, _ mysql.Row) (interface{}, error) {
	if tr, ok := GetTimeRange(ctx.Context); ok {
		return tr.From, nil
	}
	return nil, nil
}

type TimeToExpr struct{}

func (e *TimeToExpr) Resolved() bool               { return true }
func (e *TimeToExpr) IsNullable() bool             { return false }
func (e *TimeToExpr) Children() []mysql.Expression { return nil }
func (e *TimeToExpr) WithChildren(...mysql.Expression) (mysql.Expression, error) {
	return e, nil
}
func (e *TimeToExpr) String() string   { return "time_to()" }
func (e *TimeToExpr) Type() mysql.Type { return types.Timestamp }
func (e *TimeToExpr) Eval(ctx *mysql.Context, _ mysql.Row) (interface{}, error) {
	if tr, ok := GetTimeRange(ctx.Context); ok {
		return tr.To, nil
	}
	return nil, nil
}

//
// sql.Function implementations
//

type timeFromFunction struct{}

func (*timeFromFunction) isFunction() {}

func (f *timeFromFunction) FunctionName() string {
	return "time_from"
}
func (f *timeFromFunction) NewInstance(args []mysql.Expression) (mysql.Expression, error) {
	return &TimeFromExpr{}, nil
}

type timeToFunction struct{}

func (*timeToFunction) isFunction() {}

func (f *timeToFunction) FunctionName() string {
	return "time_to"
}
func (f *timeToFunction) NewInstance(args []mysql.Expression) (mysql.Expression, error) {
	return &TimeToExpr{}, nil
}

//
// FunctionProvider to register both functions
//

type TimeFuncProvider struct{}

func (p *TimeFuncProvider) Function(ctx *mysql.Context, name string) (mysql.Function, bool) {
	switch name {
	case "time_from":
		return &timeFromFunction{}, true
	case "time_to":
		return &timeToFunction{}, true
	default:
		return nil, false
	}
}