Reimplement Fprint in terms of fmt.Fprintf (#44)

This PR follows on from #40 completely implementing Fprint in terms of
fmt.Fprintf. This will be the final PR before Fprint is removed.

errors.go

@@ -115,7 +115,8 @@ func (w wrapper) Format(s fmt.State, verb rune) {
 	switch verb {
 	case 'v':
 		if s.Flag('+') {
-			fmt.Fprintf(s, "%+v: %s", w.Stacktrace()[0], w.cause.msg)
+			fmt.Fprintf(s, "%+v\n", w.Cause())
+			fmt.Fprintf(s, "%+v: %s", w.Stacktrace()[0], w.msg)
 			return
 		}
 		fallthrough
@@ -154,10 +155,6 @@ func Wrapf(err error, format string, args ...interface{}) error {
 	}
 }
 
-type causer interface {
-	Cause() error
-}
-
 // Cause returns the underlying cause of the error, if possible.
 // An error value has a cause if it implements the following
 // interface:
@@ -170,6 +167,10 @@ type causer interface {
 // be returned. If the error is nil, nil will be returned without further
 // investigation.
 func Cause(err error) error {
+	type causer interface {
+		Cause() error
+	}
+
 	for err != nil {
 		cause, ok := err.(causer)
 		if !ok {
@@ -188,15 +189,8 @@ func Cause(err error) error {
 //
 // Deprecated: Fprint will be removed in version 0.7.
 func Fprint(w io.Writer, err error) {
-	var fn func(err error)
-	fn = func(err error) {
-		if err == nil {
-			return
-		}
-		if cause, ok := err.(causer); ok {
-			fn(cause.Cause())
-		}
-		fmt.Fprintf(w, "%+v\n", err)
+	if err == nil {
+		return
 	}
-	fn(err)
+	fmt.Fprintf(w, "%+v\n", err)
 }

errors_test.go

@@ -57,13 +57,6 @@ type nilError struct{}
 
 func (nilError) Error() string { return "nil error" }
 
-type causeError struct {
-	cause error
-}
-
-func (e *causeError) Error() string { return "cause error" }
-func (e *causeError) Cause() error  { return e.cause }
-
 func TestCause(t *testing.T) {
 	x := New("error")
 	tests := []struct {
@@ -87,7 +80,7 @@ func TestCause(t *testing.T) {
 		want: io.EOF,
 	}, {
 		// caused error returns cause
-		err:  &causeError{cause: io.EOF},
+		err:  Wrap(io.EOF, "ignored"),
 		want: io.EOF,
 	}, {
 		err:  x, // return from errors.New
@@ -118,30 +111,29 @@ func TestFprintError(t *testing.T) {
 		err:  io.EOF,
 		want: "EOF\n",
 	}, {
-		// caused error returns cause
-		err: &causeError{cause: io.EOF},
+		err: Wrap(io.EOF, "cause error"),
 		want: "EOF\n" +
-			"cause error\n",
+			"github.com/pkg/errors/errors_test.go:114: cause error\n",
 	}, {
 		err:  x, // return from errors.New
-		want: "github.com/pkg/errors/errors_test.go:106: error\n",
+		want: "github.com/pkg/errors/errors_test.go:99: error\n",
 	}, {
 		err: Wrap(x, "message"),
-		want: "github.com/pkg/errors/errors_test.go:106: error\n" +
-			"github.com/pkg/errors/errors_test.go:129: message\n",
+		want: "github.com/pkg/errors/errors_test.go:99: error\n" +
+			"github.com/pkg/errors/errors_test.go:121: message\n",
 	}, {
 		err: Wrap(io.EOF, "message"),
 		want: "EOF\n" +
-			"github.com/pkg/errors/errors_test.go:133: message\n",
+			"github.com/pkg/errors/errors_test.go:125: message\n",
 	}, {
 		err: Wrap(Wrap(x, "message"), "another message"),
-		want: "github.com/pkg/errors/errors_test.go:106: error\n" +
-			"github.com/pkg/errors/errors_test.go:137: message\n" +
-			"github.com/pkg/errors/errors_test.go:137: another message\n",
+		want: "github.com/pkg/errors/errors_test.go:99: error\n" +
+			"github.com/pkg/errors/errors_test.go:129: message\n" +
+			"github.com/pkg/errors/errors_test.go:129: another message\n",
 	}, {
 		err: Wrapf(x, "message"),
-		want: "github.com/pkg/errors/errors_test.go:106: error\n" +
-			"github.com/pkg/errors/errors_test.go:142: message\n",
+		want: "github.com/pkg/errors/errors_test.go:99: error\n" +
+			"github.com/pkg/errors/errors_test.go:134: message\n",
 	}}
 
 	for i, tt := range tests {

format_test.go

@@ -2,6 +2,7 @@ package errors
 
 import (
 	"fmt"
+	"io"
 	"testing"
 )
 
@@ -22,7 +23,7 @@ func TestFormat(t *testing.T) {
 	}, {
 		New("error"),
 		"%+v",
-		"github.com/pkg/errors/format_test.go:23: error",
+		"github.com/pkg/errors/format_test.go:24: error",
 	}, {
 		Errorf("%s", "error"),
 		"%s",
@@ -34,7 +35,7 @@ func TestFormat(t *testing.T) {
 	}, {
 		Errorf("%s", "error"),
 		"%+v",
-		"github.com/pkg/errors/format_test.go:35: error",
+		"github.com/pkg/errors/format_test.go:36: error",
 	}, {
 		Wrap(New("error"), "error2"),
 		"%s",
@@ -46,11 +47,25 @@ func TestFormat(t *testing.T) {
 	}, {
 		Wrap(New("error"), "error2"),
 		"%+v",
-		"github.com/pkg/errors/format_test.go:47: error2",
+		"github.com/pkg/errors/format_test.go:48: error\n" +
+			"github.com/pkg/errors/format_test.go:48: error2",
+	}, {
+		Wrap(io.EOF, "error"),
+		"%s",
+		"error: EOF",
 	}, {
 		Wrapf(New("error"), "error%d", 2),
 		"%s",
 		"error2: error",
+	}, {
+		Wrap(io.EOF, "error"),
+		"%v",
+		"error: EOF",
+	}, {
+		Wrap(io.EOF, "error"),
+		"%+v",
+		"EOF\n" +
+			"github.com/pkg/errors/format_test.go:65: error",
 	}, {
 		Wrapf(New("error"), "error%d", 2),
 		"%v",
@@ -58,7 +73,8 @@ func TestFormat(t *testing.T) {
 	}, {
 		Wrapf(New("error"), "error%d", 2),
 		"%+v",
-		"github.com/pkg/errors/format_test.go:59: error2",
+		"github.com/pkg/errors/format_test.go:74: error\n" +
+			"github.com/pkg/errors/format_test.go:74: error2",
 	}}
 
 	for _, tt := range tests {