// 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 cmp
import (
"fmt"
"reflect"
"strings"
"unicode"
"unicode/utf8"
)
// Path is a list of PathSteps describing the sequence of operations to get
// from some root type to the current position in the value tree.
// The first Path element is always an operation-less PathStep that exists
// simply to identify the initial type.
//
// When traversing structs with embedded structs, the embedded struct will
// always be accessed as a field before traversing the fields of the
// embedded struct themselves. That is, an exported field from the
// embedded struct will never be accessed directly from the parent struct.
type Path []PathStep
// PathStep is a union-type for specific operations to traverse
// a value's tree structure. Users of this package never need to implement
// these types as values of this type will be returned by this package.
//
// Implementations of this interface are
// StructField, SliceIndex, MapIndex, Indirect, TypeAssertion, and Transform.
type PathStep interface {
String() string
// Type is the resulting type after performing the path step.
Type() reflect.Type
// Values is the resulting values after performing the path step.
// The type of each valid value is guaranteed to be identical to Type.
//
// In some cases, one or both may be invalid or have restrictions:
// • For StructField, both are not interface-able if the current field
// is unexported and the struct type is not explicitly permitted by
// AllowUnexported to traverse unexported fields.
// • For SliceIndex, one may be invalid if an element is missing from
// either the x or y slice.
// • For MapIndex, one may be invalid if an entry is missing from
// either the x or y map.
//
// The provided values must not be mutated.
Values() (vx, vy reflect.Value)
}
var (
_ PathStep = StructField{}
_ PathStep = SliceIndex{}
_ PathStep = MapIndex{}
_ PathStep = Indirect{}
_ PathStep = TypeAssertion{}
_ PathStep = Transform{}
)
func (pa *Path) push(s PathStep) {
*pa = append(*pa, s)
}
func (pa *Path) pop() {
*pa = (*pa)[:len(*pa)-1]
}
// Last returns the last PathStep in the Path.
// If the path is empty, this returns a non-nil PathStep that reports a nil Type.
func (pa Path) Last() PathStep {
return pa.Index(-1)
}
// Index returns the ith step in the Path and supports negative indexing.
// A negative index starts counting from the tail of the Path such that -1
// refers to the last step, -2 refers to the second-to-last step, and so on.
// If index is invalid, this returns a non-nil PathStep that reports a nil Type.
func (pa Path) Index(i int) PathStep {
if i < 0 {
i = len(pa) + i
}
if i < 0 || i >= len(pa) {
return pathStep{}
}
return pa[i]
}
// String returns the simplified path to a node.
// The simplified path only contains struct field accesses.
//
// For example:
// MyMap.MySlices.MyField
func (pa Path) String() string {
var ss []string
for _, s := range pa {
if _, ok := s.(StructField); ok {
ss = append(ss, s.String())
}
}
return strings.TrimPrefix(strings.Join(ss, ""), ".")
}
// GoString returns the path to a specific node using Go syntax.
//
// For example:
// (*root.MyMap["key"].(*mypkg.MyStruct).MySlices)[2][3].MyField
func (pa Path) GoString() string {
var ssPre, ssPost []string
var numIndirect int
for i, s := range pa {
var nextStep PathStep
if i+1 < len(pa) {
nextStep = pa[i+1]
}
switch s := s.(type) {
case Indirect:
numIndirect++
pPre, pPost := "(", ")"
switch nextStep.(type) {
case Indirect:
continue // Next step is indirection, so let them batch up
case StructField:
numIndirect-- // Automatic indirection on struct fields
case nil:
pPre, pPost = "", "" // Last step; no need for parenthesis
}
if numIndirect > 0 {
ssPre = append(ssPre, pPre+strings.Repeat("*", numIndirect))
ssPost = append(ssPost, pPost)
}
numIndirect = 0
continue
case Transform:
ssPre = append(ssPre, s.trans.name+"(")
ssPost = append(ssPost, ")")
continue
}
ssPost = append(ssPost, s.String())
}
for i, j := 0, len(ssPre)-1; i < j; i, j = i+1, j-1 {
ssPre[i], ssPre[j] = ssPre[j], ssPre[i]
}
return strings.Join(ssPre, "") + strings.Join(ssPost, "")
}
type pathStep struct {
typ reflect.Type
vx, vy reflect.Value
}
func (ps pathStep) Type() reflect.Type { return ps.typ }
func (ps pathStep) Values() (vx, vy reflect.Value) { return ps.vx, ps.vy }
func (ps pathStep) String() string {
if ps.typ == nil {
return "<nil>"
}
s := ps.typ.String()
if s == "" || strings.ContainsAny(s, "{}\n") {
return "root" // Type too simple or complex to print
}
return fmt.Sprintf("{%s}", s)
}
// StructField represents a struct field access on a field called Name.
type StructField struct{ *structField }
type structField struct {
pathStep
name string
idx int
// These fields are used for forcibly accessing an unexported field.
// pvx, pvy, and field are only valid if unexported is true.
unexported bool
mayForce bool // Forcibly allow visibility
pvx, pvy reflect.Value // Parent values
field reflect.StructField // Field information
}
func (sf StructField) Type() reflect.Type { return sf.typ }
func (sf StructField) Values() (vx, vy reflect.Value) {
if !sf.unexported {
return sf.vx, sf.vy // CanInterface reports true
}
// Forcibly obtain read-write access to an unexported struct field.
if sf.mayForce {
vx = retrieveUnexportedField(sf.pvx, sf.field)
vy = retrieveUnexportedField(sf.pvy, sf.field)
return vx, vy // CanInterface reports true
}
return sf.vx, sf.vy // CanInterface reports false
}
func (sf StructField) String() string { return fmt.Sprintf(".%s", sf.name) }
// Name is the field name.
func (sf StructField) Name() string { return sf.name }
// Index is the index of the field in the parent struct type.
// See reflect.Type.Field.
func (sf StructField) Index() int { return sf.idx }
// SliceIndex is an index operation on a slice or array at some index Key.
type SliceIndex struct{ *sliceIndex }
type sliceIndex struct {
pathStep
xkey, ykey int
}
func (si SliceIndex) Type() reflect.Type { return si.typ }
func (si SliceIndex) Values() (vx, vy reflect.Value) { return si.vx, si.vy }
func (si SliceIndex) String() string {
switch {
case si.xkey == si.ykey:
return fmt.Sprintf("[%d]", si.xkey)
case si.ykey == -1:
// [5->?] means "I don't know where X[5] went"
return fmt.Sprintf("[%d->?]", si.xkey)
case si.xkey == -1:
// [?->3] means "I don't know where Y[3] came from"
return fmt.Sprintf("[?->%d]", si.ykey)
default:
// [5->3] means "X[5] moved to Y[3]"
return fmt.Sprintf("[%d->%d]", si.xkey, si.ykey)
}
}
// Key is the index key; it may return -1 if in a split state
func (si SliceIndex) Key() int {
if si.xkey != si.ykey {
return -1
}
return si.xkey
}
// SplitKeys are the indexes for indexing into slices in the
// x and y values, respectively. These indexes may differ due to the
// insertion or removal of an element in one of the slices, causing
// all of the indexes to be shifted. If an index is -1, then that
// indicates that the element does not exist in the associated slice.
//
// Key is guaranteed to return -1 if and only if the indexes returned
// by SplitKeys are not the same. SplitKeys will never return -1 for
// both indexes.
func (si SliceIndex) SplitKeys() (ix, iy int) { return si.xkey, si.ykey }
// MapIndex is an index operation on a map at some index Key.
type MapIndex struct{ *mapIndex }
type mapIndex struct {
pathStep
key reflect.Value
}
func (mi MapIndex) Type() reflect.Type { return mi.typ }
func (mi MapIndex) Values() (vx, vy reflect.Value) { return mi.vx, mi.vy }
func (mi MapIndex) String() string { return fmt.Sprintf("[%#v]", mi.key) }
// Key is the value of the map key.
func (mi MapIndex) Key() reflect.Value { return mi.key }
// Indirect represents pointer indirection on the parent type.
type Indirect struct{ *indirect }
type indirect struct {
pathStep
}
func (in Indirect) Type() reflect.Type { return in.typ }
func (in Indirect) Values() (vx, vy reflect.Value) { return in.vx, in.vy }
func (in Indirect) String() string { return "*" }
// TypeAssertion represents a type assertion on an interface.
type TypeAssertion struct{ *typeAssertion }
type typeAssertion struct {
pathStep
}
func (ta TypeAssertion) Type() reflect.Type { return ta.typ }
func (ta TypeAssertion) Values() (vx, vy reflect.Value) { return ta.vx, ta.vy }
func (ta TypeAssertion) String() string { return fmt.Sprintf(".(%v)", ta.typ) }
// Transform is a transformation from the parent type to the current type.
type Transform struct{ *transform }
type transform struct {
pathStep
trans *transformer
}
func (tf Transform) Type() reflect.Type { return tf.typ }
func (tf Transform) Values() (vx, vy reflect.Value) { return tf.vx, tf.vy }
func (tf Transform) String() string { return fmt.Sprintf("%s()", tf.trans.name) }
// Name is the name of the Transformer.
func (tf Transform) Name() string { return tf.trans.name }
// Func is the function pointer to the transformer function.
func (tf Transform) Func() reflect.Value { return tf.trans.fnc }
// Option returns the originally constructed Transformer option.
// The == operator can be used to detect the exact option used.
func (tf Transform) Option() Option { return tf.trans }
// isExported reports whether the identifier is exported.
func isExported(id string) bool {
r, _ := utf8.DecodeRuneInString(id)
return unicode.IsUpper(r)
}
