func FuzzParseExpr(in []byte) int {
	_, err := ParseExpr(string(in))
	if err == nil {
		return fuzzInteresting
	}
	return fuzzMeh
}
Fuzz the expression parser.
package promql
import (
	"io"
	"github.com/prometheus/prometheus/pkg/textparse"
)
const (
	fuzzInteresting = 1
	fuzzMeh         = 0
	fuzzDiscard     = -1
)
func fuzzParseMetricWithContentType(in []byte, contentType string) int {
	p := textparse.New(in, contentType)
	var err error
	for {
		_, err = p.Next()
		if err != nil {
			break
		}
	}
	if err == io.EOF {
		err = nil
	}
	if err == nil {
		return fuzzInteresting
	}
	return fuzzMeh
}
func FuzzParseMetric(in []byte) int {
	return fuzzParseMetricWithContentType(in, "")
}
func FuzzParseOpenMetric(in []byte) int {
	return fuzzParseMetricWithContentType(in, "application/openmetrics-text")
}
func FuzzParseMetricSelector(in []byte) int {
	_, err := ParseMetricSelector(string(in))
	if err == nil {
		return fuzzInteresting
	}
	return fuzzMeh
}