Support go1.18, drop support for <go1.8

Change-Id: I676aabbd7173e6ae523e6fcedfaafcd44ba85c3a

gotestmain/gotestmain.go

@@ -42,7 +42,7 @@ type data struct {
 	Tests                 []string
 	Examples              []*doc.Example
 	HasMain               bool
-	MainStartTakesInterface bool
+	MainStartTakesFuzzers bool
 }
 
 func findTests(srcs []string) (tests []string, examples []*doc.Example, hasMain bool) {
@@ -68,10 +68,9 @@ func findTests(srcs []string) (tests []string, examples []*doc.Example, hasMain
 	return
 }
 
-// Returns true for go1.8+, where testing.MainStart takes an interface instead of a function
-// as its first argument.
-func mainStartTakesInterface() bool {
-	return reflect.TypeOf(testing.MainStart).In(0).Kind() == reflect.Interface
+// Returns true for go1.18+, where testing.MainStart takes an extra slice of fuzzers.
+func mainStartTakesFuzzers() bool {
+	return reflect.TypeOf(testing.MainStart).NumIn() > 4
 }
 
 func main() {
@@ -92,7 +91,7 @@ func main() {
 		Tests:                 tests,
 		Examples:              examples,
 		HasMain:               hasMain,
-		MainStartTakesInterface: mainStartTakesInterface(),
+		MainStartTakesFuzzers: mainStartTakesFuzzers(),
 	}
 
 	err := testMainTmpl.Execute(buf, d)
@@ -114,8 +113,10 @@ import (
 {{if not .HasMain}}
 	"os"
 {{end}}
+	"reflect"
 	"regexp"
 	"testing"
+	"time"
 
 	pkg "{{.Package}}"
 )
@@ -185,11 +186,44 @@ func (matchString) SetPanicOnExit0(bool) {
 	panic("shouldn't get here")
 }
 
+func (matchString) CoordinateFuzzing(time.Duration, int64, time.Duration, int64, int, []corpusEntry, []reflect.Type, string, string) error {
+	panic("shouldn't get here")
+}
+
+func (matchString) RunFuzzWorker(func(corpusEntry) error) error {
+	panic("shouldn't get here")
+}
+
+func (matchString) ReadCorpus(string, []reflect.Type) ([]corpusEntry, error) {
+	panic("shouldn't get here")
+}
+
+func (matchString) CheckCorpus([]interface{}, []reflect.Type) error {
+	panic("shouldn't get here")
+}
+
+func (matchString) ResetCoverage() {
+	panic("shouldn't get here")
+}
+
+func (matchString) SnapshotCoverage() {
+	panic("shouldn't get here")
+}
+
+type corpusEntry = struct {
+	Parent     string
+	Path       string
+	Data       []byte
+	Values     []interface{}
+	Generation int
+	IsSeed     bool
+}
+
 func main() {
-{{if .MainStartTakesInterface}}
-	m := testing.MainStart(matchString{}, t, nil, e)
+{{if .MainStartTakesFuzzers }}
+	m := testing.MainStart(matchString{}, t, nil, nil, e)
 {{else}}
-	m := testing.MainStart(MatchString, t, nil, e)
+	m := testing.MainStart(matchString{}, t, nil, e)
 {{end}}
 {{if .HasMain}}
 	pkg.TestMain(m)