Split function into Stack Frame Extraction and Printing

frame.go

@@ -6,6 +6,12 @@ import (
 	"github.com/pkg/errors"
 )
 
+type ErrorSet struct {
+	Error  error
+	Frames Frames
+	Parent Frames
+}
+
 type Frame struct {
 	File string
 	Line int

pperr.go

@@ -34,12 +34,18 @@ func Fprint(w io.Writer, err error) {
 }
 
 func FprintFunc(w io.Writer, err error, puts Printer) {
-	fprintFuncWithParent(w, err, puts, nil)
+	for _, e := range extractErrorSet(err, nil) {
+		puts(w, e.Error, e.Frames, e.Parent)
+	}
+}
+
+func ExtractErrorSet(err error) []ErrorSet {
+	return extractErrorSet(err, nil)
 }
 
-func fprintFuncWithParent(w io.Writer, err error, puts Printer, parent Frames) {
+func extractErrorSet(err error, parent Frames) []ErrorSet {
 	if err == nil {
-		return
+		return nil
 	}
 
 	realErr := err
@@ -53,6 +59,8 @@ func fprintFuncWithParent(w io.Writer, err error, puts Printer, parent Frames) {
 		}
 	}
 
+	var errs []ErrorSet
+
 	if withCause, ok := realErr.(interface{ Unwrap() error }); ok {
 		var causeParent Frames
 
@@ -62,10 +70,14 @@ func fprintFuncWithParent(w io.Writer, err error, puts Printer, parent Frames) {
 			causeParent = parent
 		}
 
-		fprintFuncWithParent(w, withCause.Unwrap(), puts, causeParent)
+		if es := extractErrorSet(withCause.Unwrap(), causeParent); es != nil {
+			errs = es
+		}
 	}
 
-	puts(w, err, frames, parent)
+	errs = append(errs, ErrorSet{Error: err, Frames: frames, Parent: parent})
+
+	return errs
 }
 
 func CauseType(err error) string {

pperr_test.go

@@ -42,6 +42,51 @@ func f3(native bool) error {
 	}
 }
 
+func TestExtractErrorSet(t *testing.T) {
+	assert := assert.New(t)
+
+	err := f1(true)
+
+	var buf strings.Builder
+	for _, e := range pperr.ExtractErrorSet(err) {
+		pperr.DefaultPrinter(&buf, e.Error, e.Frames, e.Parent)
+	}
+	actual := buf.String()
+	actual = regexp.MustCompile(`(?m)[^\s>]+/pperr_test.go:\d+$`).ReplaceAllString(actual, ".../pperr_test.go:NN")
+	actual = regexp.MustCompile(`(?m)[^\s>]+/go/.*:\d+$`).ReplaceAllString(actual, ".../go/...:NN")
+	actual = regexp.MustCompile(`(?m):\d+$`).ReplaceAllString(actual, ":NN")
+
+	expected := strings.TrimPrefix(`
+syscall.Errno: no such file or directory
+*fs.PathError: open not_found: no such file or directory
+*errors.withStack: from f3(): open not_found: no such file or directory
+	github.com/kanmu/pperr_test.f3
+		.../pperr_test.go:NN
+	github.com/kanmu/pperr_test.f23
+		.../pperr_test.go:NN
+	github.com/kanmu/pperr_test.f22
+		.../pperr_test.go:NN
+	github.com/kanmu/pperr_test.f21
+		.../pperr_test.go:NN
+*xerrors.wrapError: from f23: from f3(): open not_found: no such file or directory
+*fmt.wrapError: from f21(): from f23: from f3(): open not_found: no such file or directory
+*errors.withStack: from f2(): from f21(): from f23: from f3(): open not_found: no such file or directory
+	github.com/kanmu/pperr_test.f2
+		.../pperr_test.go:NN
+*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
+		.../pperr_test.go:NN
+	testing.tRunner
+		.../go/...:NN
+	runtime.goexit
+		.../go/...:NN
+`, "\n")
+
+	assert.Equal(expected, actual)
+}
+
 func TestFprint(t *testing.T) {
 	assert := assert.New(t)