diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_disable.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_disable.go
index 42afa49..fe98dcc 100644
--- a/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_disable.go
+++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_disable.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE.md file.
 
-// +build !debug
+// +build !cmp_debug
 
 package diff
 
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_enable.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_enable.go
index fd9f7f1..597b6ae 100644
--- a/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_enable.go
+++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/debug_enable.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE.md file.
 
-// +build debug
+// +build cmp_debug
 
 package diff
 
@@ -14,7 +14,7 @@
 )
 
 // The algorithm can be seen running in real-time by enabling debugging:
-//	go test -tags=debug -v
+//	go test -tags=cmp_debug -v
 //
 // Example output:
 //	=== RUN   TestDifference/#34
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go
index 260befe..3d2e426 100644
--- a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go
+++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go
@@ -85,22 +85,31 @@
 type EqualFunc func(ix int, iy int) Result
 
 // Result is the result of comparison.
-// NSame is the number of sub-elements that are equal.
-// NDiff is the number of sub-elements that are not equal.
-type Result struct{ NSame, NDiff int }
+// NumSame is the number of sub-elements that are equal.
+// NumDiff is the number of sub-elements that are not equal.
+type Result struct{ NumSame, NumDiff int }
+
+// BoolResult returns a Result that is either Equal or not Equal.
+func BoolResult(b bool) Result {
+	if b {
+		return Result{NumSame: 1} // Equal, Similar
+	} else {
+		return Result{NumDiff: 2} // Not Equal, not Similar
+	}
+}
 
 // Equal indicates whether the symbols are equal. Two symbols are equal
-// if and only if NDiff == 0. If Equal, then they are also Similar.
-func (r Result) Equal() bool { return r.NDiff == 0 }
+// if and only if NumDiff == 0. If Equal, then they are also Similar.
+func (r Result) Equal() bool { return r.NumDiff == 0 }
 
 // Similar indicates whether two symbols are similar and may be represented
 // by using the Modified type. As a special case, we consider binary comparisons
 // (i.e., those that return Result{1, 0} or Result{0, 1}) to be similar.
 //
-// The exact ratio of NSame to NDiff to determine similarity may change.
+// The exact ratio of NumSame to NumDiff to determine similarity may change.
 func (r Result) Similar() bool {
-	// Use NSame+1 to offset NSame so that binary comparisons are similar.
-	return r.NSame+1 >= r.NDiff
+	// Use NumSame+1 to offset NumSame so that binary comparisons are similar.
+	return r.NumSame+1 >= r.NumDiff
 }
 
 // Difference reports whether two lists of lengths nx and ny are equal
@@ -191,9 +200,9 @@
 	// that two lists commonly differ because elements were added to the front
 	// or end of the other list.
 	//
-	// Running the tests with the "debug" build tag prints a visualization of
-	// the algorithm running in real-time. This is educational for understanding
-	// how the algorithm works. See debug_enable.go.
+	// Running the tests with the "cmp_debug" build tag prints a visualization
+	// of the algorithm running in real-time. This is educational for
+	// understanding how the algorithm works. See debug_enable.go.
 	f = debug.Begin(nx, ny, f, &fwdPath.es, &revPath.es)
 	for {
 		// Forward search from the beginning.
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/flags/flags.go b/vendor/github.com/google/go-cmp/cmp/internal/flags/flags.go
new file mode 100644
index 0000000..a9e7fc0
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/flags/flags.go
@@ -0,0 +1,9 @@
+// Copyright 2019, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package flags
+
+// Deterministic controls whether the output of Diff should be deterministic.
+// This is only used for testing.
+var Deterministic bool
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/flags/toolchain_legacy.go b/vendor/github.com/google/go-cmp/cmp/internal/flags/toolchain_legacy.go
new file mode 100644
index 0000000..01aed0a
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/flags/toolchain_legacy.go
@@ -0,0 +1,10 @@
+// Copyright 2019, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build !go1.10
+
+package flags
+
+// AtLeastGo110 reports whether the Go toolchain is at least Go 1.10.
+const AtLeastGo110 = false
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/flags/toolchain_recent.go b/vendor/github.com/google/go-cmp/cmp/internal/flags/toolchain_recent.go
new file mode 100644
index 0000000..c0b667f
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/flags/toolchain_recent.go
@@ -0,0 +1,10 @@
+// Copyright 2019, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build go1.10
+
+package flags
+
+// AtLeastGo110 reports whether the Go toolchain is at least Go 1.10.
+const AtLeastGo110 = true
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/function/func.go b/vendor/github.com/google/go-cmp/cmp/internal/function/func.go
index 4c35ff1..ace1dbe 100644
--- a/vendor/github.com/google/go-cmp/cmp/internal/function/func.go
+++ b/vendor/github.com/google/go-cmp/cmp/internal/function/func.go
@@ -2,25 +2,34 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE.md file.
 
-// Package function identifies function types.
+// Package function provides functionality for identifying function types.
 package function
 
-import "reflect"
+import (
+	"reflect"
+	"regexp"
+	"runtime"
+	"strings"
+)
 
 type funcType int
 
 const (
 	_ funcType = iota
 
+	tbFunc  // func(T) bool
 	ttbFunc // func(T, T) bool
+	trbFunc // func(T, R) bool
 	tibFunc // func(T, I) bool
 	trFunc  // func(T) R
 
-	Equal           = ttbFunc // func(T, T) bool
-	EqualAssignable = tibFunc // func(T, I) bool; encapsulates func(T, T) bool
-	Transformer     = trFunc  // func(T) R
-	ValueFilter     = ttbFunc // func(T, T) bool
-	Less            = ttbFunc // func(T, T) bool
+	Equal             = ttbFunc // func(T, T) bool
+	EqualAssignable   = tibFunc // func(T, I) bool; encapsulates func(T, T) bool
+	Transformer       = trFunc  // func(T) R
+	ValueFilter       = ttbFunc // func(T, T) bool
+	Less              = ttbFunc // func(T, T) bool
+	ValuePredicate    = tbFunc  // func(T) bool
+	KeyValuePredicate = trbFunc // func(T, R) bool
 )
 
 var boolType = reflect.TypeOf(true)
@@ -32,10 +41,18 @@
 	}
 	ni, no := t.NumIn(), t.NumOut()
 	switch ft {
+	case tbFunc: // func(T) bool
+		if ni == 1 && no == 1 && t.Out(0) == boolType {
+			return true
+		}
 	case ttbFunc: // func(T, T) bool
 		if ni == 2 && no == 1 && t.In(0) == t.In(1) && t.Out(0) == boolType {
 			return true
 		}
+	case trbFunc: // func(T, R) bool
+		if ni == 2 && no == 1 && t.Out(0) == boolType {
+			return true
+		}
 	case tibFunc: // func(T, I) bool
 		if ni == 2 && no == 1 && t.In(0).AssignableTo(t.In(1)) && t.Out(0) == boolType {
 			return true
@@ -47,3 +64,36 @@
 	}
 	return false
 }
+
+var lastIdentRx = regexp.MustCompile(`[_\p{L}][_\p{L}\p{N}]*$`)
+
+// NameOf returns the name of the function value.
+func NameOf(v reflect.Value) string {
+	fnc := runtime.FuncForPC(v.Pointer())
+	if fnc == nil {
+		return "<unknown>"
+	}
+	fullName := fnc.Name() // e.g., "long/path/name/mypkg.(*MyType).(long/path/name/mypkg.myMethod)-fm"
+
+	// Method closures have a "-fm" suffix.
+	fullName = strings.TrimSuffix(fullName, "-fm")
+
+	var name string
+	for len(fullName) > 0 {
+		inParen := strings.HasSuffix(fullName, ")")
+		fullName = strings.TrimSuffix(fullName, ")")
+
+		s := lastIdentRx.FindString(fullName)
+		if s == "" {
+			break
+		}
+		name = s + "." + name
+		fullName = strings.TrimSuffix(fullName, s)
+
+		if i := strings.LastIndexByte(fullName, '('); inParen && i >= 0 {
+			fullName = fullName[:i]
+		}
+		fullName = strings.TrimSuffix(fullName, ".")
+	}
+	return strings.TrimSuffix(name, ".")
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/value/format.go b/vendor/github.com/google/go-cmp/cmp/internal/value/format.go
deleted file mode 100644
index 657e508..0000000
--- a/vendor/github.com/google/go-cmp/cmp/internal/value/format.go
+++ /dev/null
@@ -1,277 +0,0 @@
-// Copyright 2017, The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE.md file.
-
-// Package value provides functionality for reflect.Value types.
-package value
-
-import (
-	"fmt"
-	"reflect"
-	"strconv"
-	"strings"
-	"unicode"
-)
-
-var stringerIface = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
-
-// Format formats the value v as a string.
-//
-// This is similar to fmt.Sprintf("%+v", v) except this:
-//	* Prints the type unless it can be elided
-//	* Avoids printing struct fields that are zero
-//	* Prints a nil-slice as being nil, not empty
-//	* Prints map entries in deterministic order
-func Format(v reflect.Value, conf FormatConfig) string {
-	conf.printType = true
-	conf.followPointers = true
-	conf.realPointers = true
-	return formatAny(v, conf, nil)
-}
-
-type FormatConfig struct {
-	UseStringer        bool // Should the String method be used if available?
-	printType          bool // Should we print the type before the value?
-	PrintPrimitiveType bool // Should we print the type of primitives?
-	followPointers     bool // Should we recursively follow pointers?
-	realPointers       bool // Should we print the real address of pointers?
-}
-
-func formatAny(v reflect.Value, conf FormatConfig, visited map[uintptr]bool) string {
-	// TODO: Should this be a multi-line printout in certain situations?
-
-	if !v.IsValid() {
-		return "<non-existent>"
-	}
-	if conf.UseStringer && v.Type().Implements(stringerIface) && v.CanInterface() {
-		if (v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface) && v.IsNil() {
-			return "<nil>"
-		}
-
-		const stringerPrefix = "s" // Indicates that the String method was used
-		s := v.Interface().(fmt.Stringer).String()
-		return stringerPrefix + formatString(s)
-	}
-
-	switch v.Kind() {
-	case reflect.Bool:
-		return formatPrimitive(v.Type(), v.Bool(), conf)
-	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		return formatPrimitive(v.Type(), v.Int(), conf)
-	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		if v.Type().PkgPath() == "" || v.Kind() == reflect.Uintptr {
-			// Unnamed uints are usually bytes or words, so use hexadecimal.
-			return formatPrimitive(v.Type(), formatHex(v.Uint()), conf)
-		}
-		return formatPrimitive(v.Type(), v.Uint(), conf)
-	case reflect.Float32, reflect.Float64:
-		return formatPrimitive(v.Type(), v.Float(), conf)
-	case reflect.Complex64, reflect.Complex128:
-		return formatPrimitive(v.Type(), v.Complex(), conf)
-	case reflect.String:
-		return formatPrimitive(v.Type(), formatString(v.String()), conf)
-	case reflect.UnsafePointer, reflect.Chan, reflect.Func:
-		return formatPointer(v, conf)
-	case reflect.Ptr:
-		if v.IsNil() {
-			if conf.printType {
-				return fmt.Sprintf("(%v)(nil)", v.Type())
-			}
-			return "<nil>"
-		}
-		if visited[v.Pointer()] || !conf.followPointers {
-			return formatPointer(v, conf)
-		}
-		visited = insertPointer(visited, v.Pointer())
-		return "&" + formatAny(v.Elem(), conf, visited)
-	case reflect.Interface:
-		if v.IsNil() {
-			if conf.printType {
-				return fmt.Sprintf("%v(nil)", v.Type())
-			}
-			return "<nil>"
-		}
-		return formatAny(v.Elem(), conf, visited)
-	case reflect.Slice:
-		if v.IsNil() {
-			if conf.printType {
-				return fmt.Sprintf("%v(nil)", v.Type())
-			}
-			return "<nil>"
-		}
-		if visited[v.Pointer()] {
-			return formatPointer(v, conf)
-		}
-		visited = insertPointer(visited, v.Pointer())
-		fallthrough
-	case reflect.Array:
-		var ss []string
-		subConf := conf
-		subConf.printType = v.Type().Elem().Kind() == reflect.Interface
-		for i := 0; i < v.Len(); i++ {
-			s := formatAny(v.Index(i), subConf, visited)
-			ss = append(ss, s)
-		}
-		s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
-		if conf.printType {
-			return v.Type().String() + s
-		}
-		return s
-	case reflect.Map:
-		if v.IsNil() {
-			if conf.printType {
-				return fmt.Sprintf("%v(nil)", v.Type())
-			}
-			return "<nil>"
-		}
-		if visited[v.Pointer()] {
-			return formatPointer(v, conf)
-		}
-		visited = insertPointer(visited, v.Pointer())
-
-		var ss []string
-		keyConf, valConf := conf, conf
-		keyConf.printType = v.Type().Key().Kind() == reflect.Interface
-		keyConf.followPointers = false
-		valConf.printType = v.Type().Elem().Kind() == reflect.Interface
-		for _, k := range SortKeys(v.MapKeys()) {
-			sk := formatAny(k, keyConf, visited)
-			sv := formatAny(v.MapIndex(k), valConf, visited)
-			ss = append(ss, fmt.Sprintf("%s: %s", sk, sv))
-		}
-		s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
-		if conf.printType {
-			return v.Type().String() + s
-		}
-		return s
-	case reflect.Struct:
-		var ss []string
-		subConf := conf
-		subConf.printType = true
-		for i := 0; i < v.NumField(); i++ {
-			vv := v.Field(i)
-			if isZero(vv) {
-				continue // Elide zero value fields
-			}
-			name := v.Type().Field(i).Name
-			subConf.UseStringer = conf.UseStringer
-			s := formatAny(vv, subConf, visited)
-			ss = append(ss, fmt.Sprintf("%s: %s", name, s))
-		}
-		s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
-		if conf.printType {
-			return v.Type().String() + s
-		}
-		return s
-	default:
-		panic(fmt.Sprintf("%v kind not handled", v.Kind()))
-	}
-}
-
-func formatString(s string) string {
-	// Use quoted string if it the same length as a raw string literal.
-	// Otherwise, attempt to use the raw string form.
-	qs := strconv.Quote(s)
-	if len(qs) == 1+len(s)+1 {
-		return qs
-	}
-
-	// Disallow newlines to ensure output is a single line.
-	// Only allow printable runes for readability purposes.
-	rawInvalid := func(r rune) bool {
-		return r == '`' || r == '\n' || !unicode.IsPrint(r)
-	}
-	if strings.IndexFunc(s, rawInvalid) < 0 {
-		return "`" + s + "`"
-	}
-	return qs
-}
-
-func formatPrimitive(t reflect.Type, v interface{}, conf FormatConfig) string {
-	if conf.printType && (conf.PrintPrimitiveType || t.PkgPath() != "") {
-		return fmt.Sprintf("%v(%v)", t, v)
-	}
-	return fmt.Sprintf("%v", v)
-}
-
-func formatPointer(v reflect.Value, conf FormatConfig) string {
-	p := v.Pointer()
-	if !conf.realPointers {
-		p = 0 // For deterministic printing purposes
-	}
-	s := formatHex(uint64(p))
-	if conf.printType {
-		return fmt.Sprintf("(%v)(%s)", v.Type(), s)
-	}
-	return s
-}
-
-func formatHex(u uint64) string {
-	var f string
-	switch {
-	case u <= 0xff:
-		f = "0x%02x"
-	case u <= 0xffff:
-		f = "0x%04x"
-	case u <= 0xffffff:
-		f = "0x%06x"
-	case u <= 0xffffffff:
-		f = "0x%08x"
-	case u <= 0xffffffffff:
-		f = "0x%010x"
-	case u <= 0xffffffffffff:
-		f = "0x%012x"
-	case u <= 0xffffffffffffff:
-		f = "0x%014x"
-	case u <= 0xffffffffffffffff:
-		f = "0x%016x"
-	}
-	return fmt.Sprintf(f, u)
-}
-
-// insertPointer insert p into m, allocating m if necessary.
-func insertPointer(m map[uintptr]bool, p uintptr) map[uintptr]bool {
-	if m == nil {
-		m = make(map[uintptr]bool)
-	}
-	m[p] = true
-	return m
-}
-
-// isZero reports whether v is the zero value.
-// This does not rely on Interface and so can be used on unexported fields.
-func isZero(v reflect.Value) bool {
-	switch v.Kind() {
-	case reflect.Bool:
-		return v.Bool() == false
-	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() == 0
-	case reflect.String:
-		return v.String() == ""
-	case reflect.UnsafePointer:
-		return v.Pointer() == 0
-	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
-		return v.IsNil()
-	case reflect.Array:
-		for i := 0; i < v.Len(); i++ {
-			if !isZero(v.Index(i)) {
-				return false
-			}
-		}
-		return true
-	case reflect.Struct:
-		for i := 0; i < v.NumField(); i++ {
-			if !isZero(v.Field(i)) {
-				return false
-			}
-		}
-		return true
-	}
-	return false
-}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/value/pointer_purego.go b/vendor/github.com/google/go-cmp/cmp/internal/value/pointer_purego.go
new file mode 100644
index 0000000..0a01c47
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/value/pointer_purego.go
@@ -0,0 +1,23 @@
+// Copyright 2018, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build purego
+
+package value
+
+import "reflect"
+
+// Pointer is an opaque typed pointer and is guaranteed to be comparable.
+type Pointer struct {
+	p uintptr
+	t reflect.Type
+}
+
+// PointerOf returns a Pointer from v, which must be a
+// reflect.Ptr, reflect.Slice, or reflect.Map.
+func PointerOf(v reflect.Value) Pointer {
+	// NOTE: Storing a pointer as an uintptr is technically incorrect as it
+	// assumes that the GC implementation does not use a moving collector.
+	return Pointer{v.Pointer(), v.Type()}
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/value/pointer_unsafe.go b/vendor/github.com/google/go-cmp/cmp/internal/value/pointer_unsafe.go
new file mode 100644
index 0000000..da134ae
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/value/pointer_unsafe.go
@@ -0,0 +1,26 @@
+// Copyright 2018, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+// +build !purego
+
+package value
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// Pointer is an opaque typed pointer and is guaranteed to be comparable.
+type Pointer struct {
+	p unsafe.Pointer
+	t reflect.Type
+}
+
+// PointerOf returns a Pointer from v, which must be a
+// reflect.Ptr, reflect.Slice, or reflect.Map.
+func PointerOf(v reflect.Value) Pointer {
+	// The proper representation of a pointer is unsafe.Pointer,
+	// which is necessary if the GC ever uses a moving collector.
+	return Pointer{unsafe.Pointer(v.Pointer()), v.Type()}
+}
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/value/sort.go b/vendor/github.com/google/go-cmp/cmp/internal/value/sort.go
index fe8aa27..24fbae6 100644
--- a/vendor/github.com/google/go-cmp/cmp/internal/value/sort.go
+++ b/vendor/github.com/google/go-cmp/cmp/internal/value/sort.go
@@ -19,7 +19,7 @@
 	}
 
 	// Sort the map keys.
-	sort.Sort(valueSorter(vs))
+	sort.SliceStable(vs, func(i, j int) bool { return isLess(vs[i], vs[j]) })
 
 	// Deduplicate keys (fails for NaNs).
 	vs2 := vs[:1]
@@ -31,13 +31,6 @@
 	return vs2
 }
 
-// TODO: Use sort.Slice once Google AppEngine is on Go1.8 or above.
-type valueSorter []reflect.Value
-
-func (vs valueSorter) Len() int           { return len(vs) }
-func (vs valueSorter) Less(i, j int) bool { return isLess(vs[i], vs[j]) }
-func (vs valueSorter) Swap(i, j int)      { vs[i], vs[j] = vs[j], vs[i] }
-
 // isLess is a generic function for sorting arbitrary map keys.
 // The inputs must be of the same type and must be comparable.
 func isLess(x, y reflect.Value) bool {
@@ -49,6 +42,8 @@
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
 		return x.Uint() < y.Uint()
 	case reflect.Float32, reflect.Float64:
+		// NOTE: This does not sort -0 as less than +0
+		// since Go maps treat -0 and +0 as equal keys.
 		fx, fy := x.Float(), y.Float()
 		return fx < fy || math.IsNaN(fx) && !math.IsNaN(fy)
 	case reflect.Complex64, reflect.Complex128:
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/value/zero.go b/vendor/github.com/google/go-cmp/cmp/internal/value/zero.go
new file mode 100644
index 0000000..06a8ffd
--- /dev/null
+++ b/vendor/github.com/google/go-cmp/cmp/internal/value/zero.go
@@ -0,0 +1,48 @@
+// Copyright 2017, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package value
+
+import (
+	"math"
+	"reflect"
+)
+
+// IsZero reports whether v is the zero value.
+// This does not rely on Interface and so can be used on unexported fields.
+func IsZero(v reflect.Value) bool {
+	switch v.Kind() {
+	case reflect.Bool:
+		return v.Bool() == false
+	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 math.Float64bits(v.Float()) == 0
+	case reflect.Complex64, reflect.Complex128:
+		return math.Float64bits(real(v.Complex())) == 0 && math.Float64bits(imag(v.Complex())) == 0
+	case reflect.String:
+		return v.String() == ""
+	case reflect.UnsafePointer:
+		return v.Pointer() == 0
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
+		return v.IsNil()
+	case reflect.Array:
+		for i := 0; i < v.Len(); i++ {
+			if !IsZero(v.Index(i)) {
+				return false
+			}
+		}
+		return true
+	case reflect.Struct:
+		for i := 0; i < v.NumField(); i++ {
+			if !IsZero(v.Field(i)) {
+				return false
+			}
+		}
+		return true
+	}
+	return false
+}