Merge pull request #5 from go-playground/wrap-skip-frames

New function: WrapSkipFrames

Author: Dean Karn

chain.go

@@ -17,11 +17,11 @@ type Tag struct {
 	Value interface{}
 }
 
-func newLink(err error, prefix string) *Link {
+func newLink(err error, prefix string, skipFrames int) *Link {
 	return &Link{
 		Err:    err,
 		Prefix: prefix,
-		Source: st(),
+		Source: st(skipFrames),
 	}
 
 }
@@ -109,5 +109,5 @@ func (c Chain) AddTypes(typ ...string) Chain {
 
 // Wrap adds another contextual prefix to the error chain
 func (c Chain) Wrap(prefix string) Chain {
-	return wrap(c, prefix)
+	return wrap(c, prefix, 0)
 }

errors.go

@@ -17,21 +17,27 @@ func RegisterHelper(helper Helper) {
 
 // New creates an error with the provided text and automatically wraps it with line information.
 func New(s string) Chain {
-	return wrap(errors.New(s), "")
+	return wrap(errors.New(s), "", 0)
 }
 
 // Wrap encapsulates the error, stores a contextual prefix and automatically obtains
 // a stack trace.
 func Wrap(err error, prefix string) Chain {
-	return wrap(err, prefix)
+	return wrap(err, prefix, 0)
 }
 
-func wrap(err error, prefix string) (c Chain) {
+// WrapSkipFrames is a special version of Wrap that skips extra n frames when determining error location.
+// Normally only used when wrapping the library
+func WrapSkipFrames(err error, prefix string, n uint) Chain {
+	return wrap(err, prefix, int(n))
+}
+
+func wrap(err error, prefix string, skipFrames int) (c Chain) {
 	var ok bool
 	if c, ok = err.(Chain); ok {
-		c = append(c, newLink(err, prefix))
+		c = append(c, newLink(err, prefix, skipFrames))
 	} else {
-		c = Chain{newLink(err, prefix)}
+		c = Chain{newLink(err, prefix, skipFrames)}
 	}
 	for _, h := range helpers {
 		if !h(c, err) {

errors_test.go

@@ -9,23 +9,39 @@ import (
 
 func TestWrap(t *testing.T) {
 	defaultErr := fmt.Errorf("this is an %s", "error")
+	testWrapper := func (err error, prefix string) Chain {
+		return WrapSkipFrames(err, prefix, 1)
+	}
+
+	err0 := New("42")
 	err1 := Wrap(defaultErr, "prefix 1")
 	err2 := err1.Wrap("prefix 2")
+	err3 := testWrapper(err2, "prefix 3")
 
 	tests := []struct {
 		err Chain
 		pre string
 		suf string
 	}{
+		{
+			err: err0,
+			pre: "TestWrap: ",
+			suf: "errors_test.go:16",
+		},
 		{
 			err: err1,
 			pre: "TestWrap: ",
-			suf: "errors_test.go:12",
+			suf: "errors_test.go:17",
 		},
 		{
 			err: err2,
 			pre: "TestWrap: ",
-			suf: "errors_test.go:13",
+			suf: "errors_test.go:18",
+		},
+		{
+			err: err3,
+			pre: "TestWrap: ",
+			suf: "errors_test.go:19",
 		},
 	}
 

stack.go

@@ -112,9 +112,9 @@ func funcname(name string) string {
 	return name[i+1:]
 }
 
-func st() string {
+func st(skipFrames int) string {
 	s := callers()
-	f := fr(s, 3)
+	f := fr(s, 3 + skipFrames)
 	name := fmt.Sprintf("%n", f)
 	file := fmt.Sprintf("%+s", f)
 	line := fmt.Sprintf("%d", f)