rewrite checkpoint

vendor/github.com/kr/pretty/zero.go

@@ -0,0 +1,41 @@
+package pretty
+
+import (
+	"reflect"
+)
+
+func nonzero(v reflect.Value) bool {
+	switch v.Kind() {
+	case reflect.Bool:
+		return v.Bool()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return v.Int() != 0
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return v.Uint() != 0
+	case reflect.Float32, reflect.Float64:
+		return v.Float() != 0
+	case reflect.Complex64, reflect.Complex128:
+		return v.Complex() != complex(0, 0)
+	case reflect.String:
+		return v.String() != ""
+	case reflect.Struct:
+		for i := 0; i < v.NumField(); i++ {
+			if nonzero(getField(v, i)) {
+				return true
+			}
+		}
+		return false
+	case reflect.Array:
+		for i := 0; i < v.Len(); i++ {
+			if nonzero(v.Index(i)) {
+				return true
+			}
+		}
+		return false
+	case reflect.Map, reflect.Interface, reflect.Slice, reflect.Ptr, reflect.Chan, reflect.Func:
+		return !v.IsNil()
+	case reflect.UnsafePointer:
+		return v.Pointer() != 0
+	}
+	return true
+}