return call stack in reverse

pkg/probe/probe.go

@@ -137,11 +137,14 @@ func (e *Error) String() string {
 
 	if e.Cause != nil {
 		str := e.Cause.Error() + "\n"
-		for i, tp := range e.CallTrace {
-			if len(tp.Env) > 0 {
-				str += fmt.Sprintf(" (%d) %s:%d %s(..) Tags: [%s]\n", i, tp.Filename, tp.Line, tp.Function, strings.Join(tp.Env["Tags"], ", "))
+		callLen := len(e.CallTrace)
+		for i := callLen - 1; i >= 0; i-- {
+			if len(e.CallTrace[i].Env) > 0 {
+				str += fmt.Sprintf(" (%d) %s:%d %s(..) Tags: [%s]\n",
+					i, e.CallTrace[i].Filename, e.CallTrace[i].Line, e.CallTrace[i].Function, strings.Join(e.CallTrace[i].Env["Tags"], ", "))
 			} else {
-				str += fmt.Sprintf(" (%d) %s:%d %s(..)\n", i, tp.Filename, tp.Line, tp.Function)
+				str += fmt.Sprintf(" (%d) %s:%d %s(..)\n",
+					i, e.CallTrace[i].Filename, e.CallTrace[i].Line, e.CallTrace[i].Function)
 			}
 		}
 

pkg/probe/probe_test.go

@@ -29,15 +29,23 @@ type MySuite struct{}
 
 var _ = Suite(&MySuite{})
 
-func testDummy() *probe.Error {
+func testDummy0() *probe.Error {
 	_, e := os.Stat("this-file-cannot-exit")
-	es := probe.NewError(e)
-	es.Trace("Important info 1", "Import into 2")
-	return es
+	return probe.NewError(e)
+}
+
+func testDummy1() *probe.Error {
+	return testDummy0().Trace("DummyTag1")
+}
+
+func testDummy2() *probe.Error {
+	return testDummy1().Trace("DummyTag2")
 }
 
 func (s *MySuite) TestProbe(c *C) {
-	es := testDummy()
+	es := testDummy2().Trace("TopOfStack")
+	// Uncomment the following Println to visually test probe call trace.
+	// fmt.Println("Expecting a simulated error here.", es)
 	c.Assert(es, Not(Equals), nil)
 
 	newES := es.Trace()