fixed tests, add coverage for Wrap and Fprintf

Author: davecheney

errors.go

@@ -3,107 +3,110 @@ package errors
 
 import (
 	"fmt"
+	"io"
+	"os"
 	"runtime"
 )
 
 // New returns an error that formats as the given text.
-func New(message string) error {
-	pc, _, _, _ := runtime.Caller(1) // the caller of New
+func New(text string) error {
 	return struct {
 		error
 		pc uintptr
 	}{
-		fmt.Errorf(message),
-		pc,
+		fmt.Errorf(text),
+		pc(),
 	}
 }
 
-// Errorf returns a formatted error.
-func Errorf(format string, args ...interface{}) error {
-	pc, _, _, _ := runtime.Caller(1) // the caller of Errorf
-	return struct {
-		error
-		pc uintptr
-	}{
-		fmt.Errorf(format, args...),
-		pc,
+type e struct {
+	cause   error
+	message string
+	pc      uintptr
+}
+
+func (e *e) Error() string {
+	return e.message + ": " + e.cause.Error()
+}
+
+func (e *e) Cause() error {
+	return e.cause
+}
+
+// Wrap returns an error annotating the cause with message.
+// If cause is nil, Wrap returns nil.
+func Wrap(cause error, message string) error {
+	if cause == nil {
+		return nil
+	}
+	return &e{
+		cause:   cause,
+		message: message,
+		pc:      pc(),
 	}
 }
 
+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
-// method:
-//
-// Cause() error
+// interface:
 //
+//     type Causer interface {
+//            Cause() error
+//     }
 //
 // If the error does not implement Cause, the original error will
 // be returned. If the error is nil, nil will be returned without further
 // investigation.
 func Cause(err error) error {
-	if err == nil {
-		return nil
-	}
-	type causer interface {
-		Cause() error
-	}
-	if err, ok := err.(causer); ok {
-		return err.Cause()
+	for err != nil {
+		cause, ok := err.(causer)
+		if !ok {
+			break
+		}
+		err = cause.Cause()
 	}
 	return err
 }
 
-func underlying(err error) (error, bool) {
-	if err == nil {
-		return nil, false
-	}
-	type underlying interface {
-		underlying() error
-	}
-	if err, ok := err.(underlying); ok {
-		return err.underlying(), true
-	}
-	return nil, false
+type locationer interface {
+	Location() (string, int)
 }
 
-type traced struct {
-	error // underlying error
-	pc    uintptr
+// Print prints the error to Stderr.
+func Print(err error) {
+	Fprint(os.Stderr, err)
 }
 
-func (t *traced) underlying() error { return t.error }
+// Fprint prints the error to the supplied writer.
+// The format of the output is the same as Print.
+// If err is nil, nothing is printed.
+func Fprint(w io.Writer, err error) {
+	for err != nil {
+		location, ok := err.(locationer)
+		if ok {
+			file, line := location.Location()
+			fmt.Fprint(w, "%s:%d: ", file, line)
+		}
+		switch err := err.(type) {
+		case *e:
+			fmt.Fprintln(w, err.message)
+		default:
+			fmt.Fprintln(w, err.Error())
+		}
 
-// Trace adds caller information to the error.
-// If error is nil, nil will be returned.
-func Trace(err error) error {
-	if err == nil {
-		return nil
+		cause, ok := err.(causer)
+		if !ok {
+			break
+		}
+		err = cause.Cause()
 	}
-	pc, _, _, _ := runtime.Caller(1) // the caller of Trace
-	return traced{
-		error: err,
-		pc:    pc,
-	}
-}
-
-type annotated struct {
-	error // underlying error
-	pc uintptr
 }
 
-func (a *annotated) Cause() error { return a.error }
-
-// Annotate returns a new error annotating the error provided
-// with the message, and the location of the caller of Annotate.
-// The underlying error can be recovered by calling Cause.
-// If err is nil, nil will be returned.
-func Annotate(err error, message string) error {
-	if err == nil {
-		return nil
-	}
-	pc, _, _, _ := runtime.Caller(1) // the caller of Annotate
-	return annotated{
-		error: err,
-		pc: pc,
-	}
+func pc() uintptr {
+	pc, _, _, _ := runtime.Caller(2)
+	return pc
 }

errors_test.go

@@ -1,13 +1,14 @@
 package errors
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"reflect"
 	"testing"
 )
 
-func TestNewError(t *testing.T) {
+func TestNew(t *testing.T) {
 	tests := []struct {
 		err  string
 		want error
@@ -25,23 +26,28 @@ func TestNewError(t *testing.T) {
 	}
 }
 
-func TestNewEqualNew(t *testing.T) {
-	// test that two calls to New return the same error when called from the same location
-	var errs []error
-	for i := 0; i < 2; i++ {
-		errs = append(errs, New("error"))
-	}
-	a, b := errs[0], errs[1]
-	if !reflect.DeepEqual(a, b) {
-		t.Errorf("Expected two calls to New from the same location to give the same error: %#v, %#v", a, b)
+func TestWrapNil(t *testing.T) {
+	got := Wrap(nil, "no error")
+	if got != nil {
+		t.Errorf("Wrap(nil, \"no error\"): got %#v, expected nil", got)
 	}
 }
 
-func TestNewNotEqualNew(t *testing.T) {
-	// test that two calls to New return different errors when called from different locations
-	a, b := New("error"), New("error")
-	if reflect.DeepEqual(a, b) {
-		t.Errorf("Expected two calls to New from the different locations give the same error: %#v, %#v", a, b)
+func TestWrap(t *testing.T) {
+	tests := []struct {
+		err     error
+		message string
+		want    string
+	}{
+		{io.EOF, "read error", "read error: EOF"},
+		{Wrap(io.EOF, "read error"), "client error", "client error: read error: EOF"},
+	}
+
+	for _, tt := range tests {
+		got := Wrap(tt.err, tt.message).Error()
+		if got != tt.want {
+			t.Errorf("Wrap(%v, %q): got: %v, want %v", tt.err, tt.message, got, tt.want)
+		}
 	}
 }
 
@@ -94,23 +100,42 @@ func TestCause(t *testing.T) {
 	}
 }
 
-func TestTraceNotEqual(t *testing.T) {
-	// test that two calls to trace do not return identical errors
-	err := New("error")
-	a := err
-	var errs []error
-	for i := 0; i < 2; i++ {
-		err = Trace(err)
-		errs = append(errs, err)
-	}
-	b, c := errs[0], errs[1]
-	if reflect.DeepEqual(a, b) {
-		t.Errorf("a and b equal: %#v, %#v", a, b)
-	}
-	if reflect.DeepEqual(b, c) {
-		t.Errorf("b and c equal: %#v, %#v", b, c)
-	}
-	if reflect.DeepEqual(a, c) {
-		t.Errorf("a and c equal: %#v, %#v", a, c)
+func TestFprint(t *testing.T) {
+	x := New("error")
+	tests := []struct {
+		err  error
+		want string
+	}{{
+		// nil error is nil
+		err: nil,
+	}, {
+		// explicit nil error is nil
+		err: (error)(nil),
+	}, {
+		// uncaused error is unaffected
+		err:  io.EOF,
+		want: "EOF\n",
+	}, {
+		// caused error returns cause
+		err:  &causeError{cause: io.EOF},
+		want: "cause error\nEOF\n",
+	}, {
+		err:  x, // return from errors.New
+		want: "error\n",
+	}, {
+		err:  Wrap(x, "message"),
+		want: "message\nerror\n",
+	}, {
+		err:  Wrap(Wrap(x, "message"), "another message"),
+		want: "another message\nmessage\nerror\n",
+	}}
+
+	for i, tt := range tests {
+		var w bytes.Buffer
+		Fprint(&w, tt.err)
+		got := w.String()
+		if got != tt.want {
+			t.Errorf("test %d: Fprint(w, %q): got %q, want %q", i+1, tt.err, got, tt.want)
+		}
 	}
 }