Add TopFrame function

frame.go

@@ -6,6 +6,27 @@ import (
 	"github.com/pkg/errors"
 )
 
+type ErrorSets []ErrorSet
+
+func (es ErrorSets) TopFrame() *Frame {
+	if len(es) == 0 {
+		return nil
+	} else if len(es[0].Frames) == 0 {
+		return nil
+	}
+
+	top := es[0].Frames
+
+	if p := es[0].Parent; p != nil {
+		top = top.Exclude(p)
+	}
+	if len(top) == 0 {
+		return nil
+	}
+
+	return top[0]
+}
+
 type ErrorSet struct {
 	Error  error
 	Frames Frames

pperr.go

@@ -34,16 +34,16 @@ func Fprint(w io.Writer, err error) {
 }
 
 func FprintFunc(w io.Writer, err error, puts Printer) {
-	for _, e := range extractErrorSet(err, nil) {
+	for _, e := range extractErrorSets(err, nil) {
 		puts(w, e.Error, e.Frames, e.Parent)
 	}
 }
 
-func ExtractErrorSet(err error) []ErrorSet {
-	return extractErrorSet(err, nil)
+func ExtractErrorSets(err error) ErrorSets {
+	return extractErrorSets(err, nil)
 }
 
-func extractErrorSet(err error, parent Frames) []ErrorSet {
+func extractErrorSets(err error, parent Frames) []ErrorSet {
 	if err == nil {
 		return nil
 	}
@@ -70,7 +70,7 @@ func extractErrorSet(err error, parent Frames) []ErrorSet {
 			causeParent = parent
 		}
 
-		if es := extractErrorSet(withCause.Unwrap(), causeParent); es != nil {
+		if es := extractErrorSets(withCause.Unwrap(), causeParent); es != nil {
 			errs = es
 		}
 	}

pperr_test.go

@@ -42,13 +42,13 @@ func f3(native bool) error {
 	}
 }
 
-func TestExtractErrorSet(t *testing.T) {
+func TestExtractErrorSets(t *testing.T) {
 	assert := assert.New(t)
 
 	err := f1(true)
 
 	var buf strings.Builder
-	for _, e := range pperr.ExtractErrorSet(err) {
+	for _, e := range pperr.ExtractErrorSets(err) {
 		pperr.DefaultPrinter(&buf, e.Error, e.Frames, e.Parent)
 	}
 	actual := buf.String()
@@ -76,7 +76,7 @@ syscall.Errno: no such file or directory
 *errors.withStack: from f1(): from f2(): from f21(): from f23: from f3(): open not_found: no such file or directory
 	github.com/kanmu/pperr_test.f1
 		.../pperr_test.go:NN
-	github.com/kanmu/pperr_test.TestExtractErrorSet
+	github.com/kanmu/pperr_test.TestExtractErrorSets
 		.../pperr_test.go:NN
 	testing.tRunner
 		.../go/...:NN