Add json.Marshaler support to the Frame type.

json_test.go

@@ -0,0 +1,29 @@
+package errors
+
+import (
+	"encoding/json"
+	"regexp"
+	"testing"
+)
+
+func TestFrameMarshalJSON(t *testing.T) {
+	var tests = []struct {
+		Frame
+		want string
+	}{{
+		initpc,
+		`^"github.com/pkg/errors.init(.ializers)? .+/github.com/pkg/errors/stack_test.go:\d+"$`,
+	}, {
+		0,
+		`^"unknown"$`,
+	}}
+	for i, tt := range tests {
+		got, err := json.Marshal(tt.Frame)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !regexp.MustCompile(tt.want).Match(got) {
+			t.Errorf("test %d: MarshalJSON:\n got %q\n want %q", i+1, string(got), tt.want)
+		}
+	}
+}

stack.go

@@ -1,6 +1,7 @@
 package errors
 
 import (
+	"encoding/json"
 	"fmt"
 	"io"
 	"path"
@@ -83,6 +84,18 @@ func (f Frame) Format(s fmt.State, verb rune) {
 	}
 }
 
+// MarshalJSON formats a stacktrace Frame for easy inclusion in JSON stack
+// traces. The format is the same as that of fmt.Format("%+v"), but without
+// newlines or tabs.
+func (f Frame) MarshalJSON() ([]byte, error) {
+	name := f.name()
+	if name == "unknown" {
+		return json.Marshal(name)
+	}
+	str := fmt.Sprintf("%s %s:%d", name, f.file(), f.line())
+	return json.Marshal(str)
+}
+
 // StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
 type StackTrace []Frame