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// 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 file.
package cmpopts
import (
"fmt"
"reflect"
"strings"
"github.com/google/go-cmp/cmp"
)
// filterField returns a new Option where opt is only evaluated on paths that
// include a specific exported field on a single struct type.
// The struct type is specified by passing in a value of that type.
//
// The name may be a dot-delimited string (e.g., "Foo.Bar") to select a
// specific sub-field that is embedded or nested within the parent struct.
func filterField(typ interface{}, name string, opt cmp.Option) cmp.Option {
// TODO: This is currently unexported over concerns of how helper filters
// can be composed together easily.
// TODO: Add tests for FilterField.
sf := newStructFilter(typ, name)
return cmp.FilterPath(sf.filter, opt)
}
type structFilter struct {
t reflect.Type // The root struct type to match on
ft fieldTree // Tree of fields to match on
}
func newStructFilter(typ interface{}, names ...string) structFilter {
// TODO: Perhaps allow * as a special identifier to allow ignoring any
// number of path steps until the next field match?
// This could be useful when a concrete struct gets transformed into
// an anonymous struct where it is not possible to specify that by type,
// but the transformer happens to provide guarantees about the names of
// the transformed fields.
t := reflect.TypeOf(typ)
if t == nil || t.Kind() != reflect.Struct {
panic(fmt.Sprintf("%T must be a non-pointer struct", typ))
}
var ft fieldTree
for _, name := range names {
cname, err := canonicalName(t, name)
if err != nil {
panic(fmt.Sprintf("%s: %v", strings.Join(cname, "."), err))
}
ft.insert(cname)
}
return structFilter{t, ft}
}
func (sf structFilter) filter(p cmp.Path) bool {
for i, ps := range p {
if ps.Type().AssignableTo(sf.t) && sf.ft.matchPrefix(p[i+1:]) {
return true
}
}
return false
}
// fieldTree represents a set of dot-separated identifiers.
//
// For example, inserting the following selectors:
//
// Foo
// Foo.Bar.Baz
// Foo.Buzz
// Nuka.Cola.Quantum
//
// Results in a tree of the form:
//
// {sub: {
// "Foo": {ok: true, sub: {
// "Bar": {sub: {
// "Baz": {ok: true},
// }},
// "Buzz": {ok: true},
// }},
// "Nuka": {sub: {
// "Cola": {sub: {
// "Quantum": {ok: true},
// }},
// }},
// }}
type fieldTree struct {
ok bool // Whether this is a specified node
sub map[string]fieldTree // The sub-tree of fields under this node
}
// insert inserts a sequence of field accesses into the tree.
func (ft *fieldTree) insert(cname []string) {
if ft.sub == nil {
ft.sub = make(map[string]fieldTree)
}
if len(cname) == 0 {
ft.ok = true
return
}
sub := ft.sub[cname[0]]
sub.insert(cname[1:])
ft.sub[cname[0]] = sub
}
// matchPrefix reports whether any selector in the fieldTree matches
// the start of path p.
func (ft fieldTree) matchPrefix(p cmp.Path) bool {
for _, ps := range p {
switch ps := ps.(type) {
case cmp.StructField:
ft = ft.sub[ps.Name()]
if ft.ok {
return true
}
if len(ft.sub) == 0 {
return false
}
case cmp.Indirect:
default:
return false
}
}
return false
}
// canonicalName returns a list of identifiers where any struct field access
// through an embedded field is expanded to include the names of the embedded
// types themselves.
//
// For example, suppose field "Foo" is not directly in the parent struct,
// but actually from an embedded struct of type "Bar". Then, the canonical name
// of "Foo" is actually "Bar.Foo".
//
// Suppose field "Foo" is not directly in the parent struct, but actually
// a field in two different embedded structs of types "Bar" and "Baz".
// Then the selector "Foo" causes a panic since it is ambiguous which one it
// refers to. The user must specify either "Bar.Foo" or "Baz.Foo".
func canonicalName(t reflect.Type, sel string) ([]string, error) {
var name string
sel = strings.TrimPrefix(sel, ".")
if sel == "" {
return nil, fmt.Errorf("name must not be empty")
}
if i := strings.IndexByte(sel, '.'); i < 0 {
name, sel = sel, ""
} else {
name, sel = sel[:i], sel[i:]
}
// Type must be a struct or pointer to struct.
if t.Kind() == reflect.Ptr {
t = t.Elem()
}
if t.Kind() != reflect.Struct {
return nil, fmt.Errorf("%v must be a struct", t)
}
// Find the canonical name for this current field name.
// If the field exists in an embedded struct, then it will be expanded.
sf, _ := t.FieldByName(name)
if !isExported(name) {
// Avoid using reflect.Type.FieldByName for unexported fields due to
// buggy behavior with regard to embeddeding and unexported fields.
// See https://golang.org/issue/4876 for details.
sf = reflect.StructField{}
for i := 0; i < t.NumField() && sf.Name == ""; i++ {
if t.Field(i).Name == name {
sf = t.Field(i)
}
}
}
if sf.Name == "" {
return []string{name}, fmt.Errorf("does not exist")
}
var ss []string
for i := range sf.Index {
ss = append(ss, t.FieldByIndex(sf.Index[:i+1]).Name)
}
if sel == "" {
return ss, nil
}
ssPost, err := canonicalName(sf.Type, sel)
return append(ss, ssPost...), err
}
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