feat(errors): extract pkg/errors stacktraces

Author: kattrali

Diff for: CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## TBD
 
+### Enhancements
+
+* Extract stacktrace contents on errors wrapped by
+  [`pkg/errors`](https://github.com/pkg/errors).
+
 ### Bug fixes
 
 * Send web framework name with severity reason if set. Previously this value was

Diff for: errors/error.go

@@ -4,6 +4,7 @@ package errors
 import (
 	"bytes"
 	"fmt"
+	"github.com/pkg/errors"
 	"reflect"
 	"runtime"
 )
@@ -33,6 +34,11 @@ type ErrorWithStackFrames interface {
 	StackFrames() []StackFrame
 }
 
+type errorWithStack interface {
+	StackTrace() errors.StackTrace
+	Error() string
+}
+
 // New makes an Error from the given value. If that value is already an
 // error then it will be used directly, if not, it will be passed to
 // fmt.Errorf("%v"). The skip parameter indicates how far up the stack
@@ -48,6 +54,16 @@ func New(e interface{}, skip int) *Error {
 			Err:   e,
 			stack: e.Callers(),
 		}
+	case errorWithStack:
+		trace := e.StackTrace()
+		stack := make([]uintptr, len(trace))
+		for i, ptr := range trace {
+			stack[i] = uintptr(ptr) - 1
+		}
+		return &Error{
+			Err:   e,
+			stack: stack,
+		}
 	case ErrorWithStackFrames:
 		stack := make([]uintptr, len(e.StackFrames()))
 		for i, frame := range e.StackFrames() {

Diff for: errors/error_test.go

@@ -4,8 +4,11 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"runtime"
 	"strings"
 	"testing"
+
+	"github.com/pkg/errors"
 )
 
 // fixture functions doing work to avoid inlining
@@ -44,7 +47,7 @@ func TestParsePanicStack(t *testing.T) {
 		}
 		expected := []StackFrame{
 			StackFrame{Name: "TestParsePanicStack.func1", File: "errors/error_test.go"},
-			StackFrame{Name: "a", File: "errors/error_test.go", LineNumber: 13},
+			StackFrame{Name: "a", File: "errors/error_test.go", LineNumber: 16},
 		}
 		assertStacksMatch(t, expected, err.StackFrames())
 	}()
@@ -88,7 +91,7 @@ func TestSkipWorks(t *testing.T) {
 		}
 
 		expected := []StackFrame{
-			StackFrame{Name: "a", File: "errors/error_test.go", LineNumber: 13},
+			StackFrame{Name: "a", File: "errors/error_test.go", LineNumber: 16},
 		}
 
 		assertStacksMatch(t, expected, err.StackFrames())
@@ -182,6 +185,26 @@ func TestNewError(t *testing.T) {
 	}
 }
 
+func TestUnwrapPkgError(t *testing.T) {
+	_, _, line, ok := runtime.Caller(0) // grab line immediately before error generator
+	top := func() error {
+		err := fmt.Errorf("OH NO")
+		return errors.Wrap(err, "failed") // the correct line for the top of the stack
+	}
+	unwrapped := New(top(), 0) // if errors.StackTrace detection fails, this line will be top of stack
+	if !ok {
+		t.Fatalf("Something has gone wrong with loading the current stack")
+	}
+	if unwrapped.Error() != "failed: OH NO" {
+		t.Errorf("Failed to unwrap error: %s", unwrapped.Error())
+	}
+	expected := []StackFrame{
+		StackFrame{Name: "TestUnwrapPkgError.func1", File: "errors/error_test.go", LineNumber: line + 3},
+		StackFrame{Name: "TestUnwrapPkgError", File: "errors/error_test.go", LineNumber: line + 5},
+	}
+	assertStacksMatch(t, expected, unwrapped.StackFrames())
+}
+
 func ExampleErrorf() {
 	for i := 1; i <= 2; i++ {
 		if i%2 == 1 {