Helper function for retrieving root stack trace from error

errors.go

@@ -267,3 +267,42 @@ func Cause(err error) error {
 	}
 	return err
 }
+
+// Trace returns the underlying stack trace of the error, if possible.
+// An error value has a stack trace if it implements the following
+// interface:
+//
+//     type stackTracer interface {
+//            StackTrace() errors.StackTrace
+//     }
+//
+// If the error does not implement StackTrace, nil will be returned.
+// If the error is nil, nil will be returned without further
+// investigation.
+func Trace(err error) (frames []Frame) {
+	if err == nil {
+		return nil
+	}
+
+	type stackTracer interface {
+		StackTrace() StackTrace
+	}
+
+	type causer interface {
+		Cause() error
+	}
+
+	for err != nil {
+		if stackTrace, ok := err.(stackTracer); ok {
+			frames = ([]Frame)(stackTrace.StackTrace())
+		}
+
+		if cause, ok := err.(causer); ok {
+			err = cause.Cause()
+		} else {
+			break
+		}
+	}
+
+	return
+}

stack.go

@@ -11,13 +11,18 @@ import (
 // Frame represents a program counter inside a stack frame.
 type Frame uintptr
 
+// Name returns the name of function for this Frame's pc.
+func (f Frame) Name() string {
+	return funcname(runtime.FuncForPC(f.pc()).Name())
+}
+
 // pc returns the program counter for this frame;
 // multiple frames may have the same PC value.
 func (f Frame) pc() uintptr { return uintptr(f) - 1 }
 
-// file returns the full path to the file that contains the
+// File returns the full path to the file that contains the
 // function for this Frame's pc.
-func (f Frame) file() string {
+func (f Frame) File() string {
 	fn := runtime.FuncForPC(f.pc())
 	if fn == nil {
 		return "unknown"
@@ -26,9 +31,9 @@ func (f Frame) file() string {
 	return file
 }
 
-// line returns the line number of source code of the
+// Line returns the line number of source code of the
 // function for this Frame's pc.
-func (f Frame) line() int {
+func (f Frame) Line() int {
 	fn := runtime.FuncForPC(f.pc())
 	if fn == nil {
 		return 0
@@ -62,13 +67,12 @@ func (f Frame) Format(s fmt.State, verb rune) {
 				fmt.Fprintf(s, "%s\n\t%s", fn.Name(), file)
 			}
 		default:
-			io.WriteString(s, path.Base(f.file()))
+			io.WriteString(s, path.Base(f.File()))
 		}
 	case 'd':
-		fmt.Fprintf(s, "%d", f.line())
+		fmt.Fprintf(s, "%d", f.Line())
 	case 'n':
-		name := runtime.FuncForPC(f.pc()).Name()
-		io.WriteString(s, funcname(name))
+		io.WriteString(s, f.Name())
 	case 'v':
 		f.Format(s, 's')
 		io.WriteString(s, ":")

stack_test.go

@@ -33,7 +33,7 @@ func TestFrameLine(t *testing.T) {
 	}}
 
 	for _, tt := range tests {
-		got := tt.Frame.line()
+		got := tt.Frame.Line()
 		want := tt.want
 		if want != got {
 			t.Errorf("Frame(%v): want: %v, got: %v", uintptr(tt.Frame), want, got)