vendor/github.com/google/go-cmp/cmp/options.go - bbsim - Gitiles

 // 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"
 	"regexp"
 	"strings"

 	"github.com/google/go-cmp/cmp/internal/function"
 )

 // Option configures for specific behavior of Equal and Diff. In particular,
 // the fundamental Option functions (Ignore, Transformer, and Comparer),
 // configure how equality is determined.
 //
 // The fundamental options may be composed with filters (FilterPath and
 // FilterValues) to control the scope over which they are applied.
 //
 // The cmp/cmpopts package provides helper functions for creating options that
 // may be used with Equal and Diff.
 type Option interface {
 	// filter applies all filters and returns the option that remains.
 	// Each option may only read s.curPath and call s.callTTBFunc.
 	//
 	// An Options is returned only if multiple comparers or transformers
 	// can apply simultaneously and will only contain values of those types
 	// or sub-Options containing values of those types.
 	filter(s *state, t reflect.Type, vx, vy reflect.Value) applicableOption
 }

 // applicableOption represents the following types:
 //	Fundamental: ignore | validator | *comparer | *transformer
 //	Grouping:    Options
 type applicableOption interface {
 	Option

 	// apply executes the option, which may mutate s or panic.
 	apply(s *state, vx, vy reflect.Value)
 }

 // coreOption represents the following types:
 //	Fundamental: ignore | validator | *comparer | *transformer
 //	Filters:     *pathFilter | *valuesFilter
 type coreOption interface {
 	Option
 	isCore()
 }

 type core struct{}

 func (core) isCore() {}

 // Options is a list of Option values that also satisfies the Option interface.
 // Helper comparison packages may return an Options value when packing multiple
 // Option values into a single Option. When this package processes an Options,
 // it will be implicitly expanded into a flat list.
 //
 // Applying a filter on an Options is equivalent to applying that same filter
 // on all individual options held within.
 type Options []Option

 func (opts Options) filter(s *state, t reflect.Type, vx, vy reflect.Value) (out applicableOption) {
 	for _, opt := range opts {
 		switch opt := opt.filter(s, t, vx, vy); opt.(type) {
 		case ignore:
 			return ignore{} // Only ignore can short-circuit evaluation
 		case validator:
 			out = validator{} // Takes precedence over comparer or transformer
 		case *comparer, *transformer, Options:
 			switch out.(type) {
 			case nil:
 				out = opt
 			case validator:
 				// Keep validator
 			case *comparer, *transformer, Options:
 				out = Options{out, opt} // Conflicting comparers or transformers
 			}
 		}
 	}
 	return out
 }

 func (opts Options) apply(s *state, _, _ reflect.Value) {
 	const warning = "ambiguous set of applicable options"
 	const help = "consider using filters to ensure at most one Comparer or Transformer may apply"
 	var ss []string
 	for _, opt := range flattenOptions(nil, opts) {
 		ss = append(ss, fmt.Sprint(opt))
 	}
 	set := strings.Join(ss, "\n\t")
 	panic(fmt.Sprintf("%s at %#v:\n\t%s\n%s", warning, s.curPath, set, help))
 }

 func (opts Options) String() string {
 	var ss []string
 	for _, opt := range opts {
 		ss = append(ss, fmt.Sprint(opt))
 	}
 	return fmt.Sprintf("Options{%s}", strings.Join(ss, ", "))
 }

 // FilterPath returns a new Option where opt is only evaluated if filter f
 // returns true for the current Path in the value tree.
 //
 // This filter is called even if a slice element or map entry is missing and
 // provides an opportunity to ignore such cases. The filter function must be
 // symmetric such that the filter result is identical regardless of whether the
 // missing value is from x or y.
 //
 // The option passed in may be an Ignore, Transformer, Comparer, Options, or
 // a previously filtered Option.
 func FilterPath(f func(Path) bool, opt Option) Option {
 	if f == nil {
 		panic("invalid path filter function")
 	}
 	if opt := normalizeOption(opt); opt != nil {
 		return &pathFilter{fnc: f, opt: opt}
 	}
 	return nil
 }

 type pathFilter struct {
 	core
 	fnc func(Path) bool
 	opt Option
 }

 func (f pathFilter) filter(s *state, t reflect.Type, vx, vy reflect.Value) applicableOption {
 	if f.fnc(s.curPath) {
 		return f.opt.filter(s, t, vx, vy)
 	}
 	return nil
 }

 func (f pathFilter) String() string {
 	return fmt.Sprintf("FilterPath(%s, %v)", function.NameOf(reflect.ValueOf(f.fnc)), f.opt)
 }

 // FilterValues returns a new Option where opt is only evaluated if filter f,
 // which is a function of the form "func(T, T) bool", returns true for the
 // current pair of values being compared. If either value is invalid or
 // the type of the values is not assignable to T, then this filter implicitly
 // returns false.
 //
 // The filter function must be
 // symmetric (i.e., agnostic to the order of the inputs) and
 // deterministic (i.e., produces the same result when given the same inputs).
 // If T is an interface, it is possible that f is called with two values with
 // different concrete types that both implement T.
 //
 // The option passed in may be an Ignore, Transformer, Comparer, Options, or
 // a previously filtered Option.
 func FilterValues(f interface{}, opt Option) Option {
 	v := reflect.ValueOf(f)
 	if !function.IsType(v.Type(), function.ValueFilter) || v.IsNil() {
 		panic(fmt.Sprintf("invalid values filter function: %T", f))
 	}
 	if opt := normalizeOption(opt); opt != nil {
 		vf := &valuesFilter{fnc: v, opt: opt}
 		if ti := v.Type().In(0); ti.Kind() != reflect.Interface || ti.NumMethod() > 0 {
 			vf.typ = ti
 		}
 		return vf
 	}
 	return nil
 }

 type valuesFilter struct {
 	core
 	typ reflect.Type  // T
 	fnc reflect.Value // func(T, T) bool
 	opt Option
 }

 func (f valuesFilter) filter(s *state, t reflect.Type, vx, vy reflect.Value) applicableOption {
 	if !vx.IsValid() || !vx.CanInterface() || !vy.IsValid() || !vy.CanInterface() {
 		return nil
 	}
 	if (f.typ == nil || t.AssignableTo(f.typ)) && s.callTTBFunc(f.fnc, vx, vy) {
 		return f.opt.filter(s, t, vx, vy)
 	}
 	return nil
 }

 func (f valuesFilter) String() string {
 	return fmt.Sprintf("FilterValues(%s, %v)", function.NameOf(f.fnc), f.opt)
 }

 // Ignore is an Option that causes all comparisons to be ignored.
 // This value is intended to be combined with FilterPath or FilterValues.
 // It is an error to pass an unfiltered Ignore option to Equal.
 func Ignore() Option { return ignore{} }

 type ignore struct{ core }

 func (ignore) isFiltered() bool                                                     { return false }
 func (ignore) filter(_ *state, _ reflect.Type, _, _ reflect.Value) applicableOption { return ignore{} }
 func (ignore) apply(s *state, _, _ reflect.Value)                                   { s.report(true, reportByIgnore) }
 func (ignore) String() string                                                       { return "Ignore()" }

 // validator is a sentinel Option type to indicate that some options could not
 // be evaluated due to unexported fields, missing slice elements, or
 // missing map entries. Both values are validator only for unexported fields.
 type validator struct{ core }

 func (validator) filter(_ *state, _ reflect.Type, vx, vy reflect.Value) applicableOption {
 	if !vx.IsValid() || !vy.IsValid() {
 		return validator{}
 	}
 	if !vx.CanInterface() || !vy.CanInterface() {
 		return validator{}
 	}
 	return nil
 }
 func (validator) apply(s *state, vx, vy reflect.Value) {
 	// Implies missing slice element or map entry.
 	if !vx.IsValid() || !vy.IsValid() {
 		s.report(vx.IsValid() == vy.IsValid(), 0)
 		return
 	}

 	// Unable to Interface implies unexported field without visibility access.
 	if !vx.CanInterface() || !vy.CanInterface() {
 		const help = "consider using a custom Comparer; if you control the implementation of type, you can also consider using an Exporter, AllowUnexported, or cmpopts.IgnoreUnexported"
 		var name string
 		if t := s.curPath.Index(-2).Type(); t.Name() != "" {
 			// Named type with unexported fields.
 			name = fmt.Sprintf("%q.%v", t.PkgPath(), t.Name()) // e.g., "path/to/package".MyType
 		} else {
 			// Unnamed type with unexported fields. Derive PkgPath from field.
 			var pkgPath string
 			for i := 0; i < t.NumField() && pkgPath == ""; i++ {
 				pkgPath = t.Field(i).PkgPath
 			}
 			name = fmt.Sprintf("%q.(%v)", pkgPath, t.String()) // e.g., "path/to/package".(struct { a int })
 		}
 		panic(fmt.Sprintf("cannot handle unexported field at %#v:\n\t%v\n%s", s.curPath, name, help))
 	}

 	panic("not reachable")
 }

 // identRx represents a valid identifier according to the Go specification.
 const identRx = `[_\p{L}][_\p{L}\p{N}]*`

 var identsRx = regexp.MustCompile(`^` + identRx + `(\.` + identRx + `)*$`)

 // Transformer returns an Option that applies a transformation function that
 // converts values of a certain type into that of another.
 //
 // The transformer f must be a function "func(T) R" that converts values of
 // type T to those of type R and is implicitly filtered to input values
 // assignable to T. The transformer must not mutate T in any way.
 //
 // To help prevent some cases of infinite recursive cycles applying the
 // same transform to the output of itself (e.g., in the case where the
 // input and output types are the same), an implicit filter is added such that
 // a transformer is applicable only if that exact transformer is not already
 // in the tail of the Path since the last non-Transform step.
 // For situations where the implicit filter is still insufficient,
 // consider using cmpopts.AcyclicTransformer, which adds a filter
 // to prevent the transformer from being recursively applied upon itself.
 //
 // The name is a user provided label that is used as the Transform.Name in the
 // transformation PathStep (and eventually shown in the Diff output).
 // The name must be a valid identifier or qualified identifier in Go syntax.
 // If empty, an arbitrary name is used.
 func Transformer(name string, f interface{}) Option {
 	v := reflect.ValueOf(f)
 	if !function.IsType(v.Type(), function.Transformer) || v.IsNil() {
 		panic(fmt.Sprintf("invalid transformer function: %T", f))
 	}
 	if name == "" {
 		name = function.NameOf(v)
 		if !identsRx.MatchString(name) {
 			name = "λ" // Lambda-symbol as placeholder name
 		}
 	} else if !identsRx.MatchString(name) {
 		panic(fmt.Sprintf("invalid name: %q", name))
 	}
 	tr := &transformer{name: name, fnc: reflect.ValueOf(f)}
 	if ti := v.Type().In(0); ti.Kind() != reflect.Interface || ti.NumMethod() > 0 {
 		tr.typ = ti
 	}
 	return tr
 }

 type transformer struct {
 	core
 	name string
 	typ  reflect.Type  // T
 	fnc  reflect.Value // func(T) R
 }

 func (tr *transformer) isFiltered() bool { return tr.typ != nil }

 func (tr *transformer) filter(s *state, t reflect.Type, _, _ reflect.Value) applicableOption {
 	for i := len(s.curPath) - 1; i >= 0; i-- {
 		if t, ok := s.curPath[i].(Transform); !ok {
 			break // Hit most recent non-Transform step
 		} else if tr == t.trans {
 			return nil // Cannot directly use same Transform
 		}
 	}
 	if tr.typ == nil || t.AssignableTo(tr.typ) {
 		return tr
 	}
 	return nil
 }

 func (tr *transformer) apply(s *state, vx, vy reflect.Value) {
 	step := Transform{&transform{pathStep{typ: tr.fnc.Type().Out(0)}, tr}}
 	vvx := s.callTRFunc(tr.fnc, vx, step)
 	vvy := s.callTRFunc(tr.fnc, vy, step)
 	step.vx, step.vy = vvx, vvy
 	s.compareAny(step)
 }

 func (tr transformer) String() string {
 	return fmt.Sprintf("Transformer(%s, %s)", tr.name, function.NameOf(tr.fnc))
 }

 // Comparer returns an Option that determines whether two values are equal
 // to each other.
 //
 // The comparer f must be a function "func(T, T) bool" and is implicitly
 // filtered to input values assignable to T. If T is an interface, it is
 // possible that f is called with two values of different concrete types that
 // both implement T.
 //
 // The equality function must be:
 //	• Symmetric: equal(x, y) == equal(y, x)
 //	• Deterministic: equal(x, y) == equal(x, y)
 //	• Pure: equal(x, y) does not modify x or y
 func Comparer(f interface{}) Option {
 	v := reflect.ValueOf(f)
 	if !function.IsType(v.Type(), function.Equal) || v.IsNil() {
 		panic(fmt.Sprintf("invalid comparer function: %T", f))
 	}
 	cm := &comparer{fnc: v}
 	if ti := v.Type().In(0); ti.Kind() != reflect.Interface || ti.NumMethod() > 0 {
 		cm.typ = ti
 	}
 	return cm
 }

 type comparer struct {
 	core
 	typ reflect.Type  // T
 	fnc reflect.Value // func(T, T) bool
 }

 func (cm *comparer) isFiltered() bool { return cm.typ != nil }

 func (cm *comparer) filter(_ *state, t reflect.Type, _, _ reflect.Value) applicableOption {
 	if cm.typ == nil || t.AssignableTo(cm.typ) {
 		return cm
 	}
 	return nil
 }

 func (cm *comparer) apply(s *state, vx, vy reflect.Value) {
 	eq := s.callTTBFunc(cm.fnc, vx, vy)
 	s.report(eq, reportByFunc)
 }

 func (cm comparer) String() string {
 	return fmt.Sprintf("Comparer(%s)", function.NameOf(cm.fnc))
 }

 // Exporter returns an Option that specifies whether Equal is allowed to
 // introspect into the unexported fields of certain struct types.
 //
 // Users of this option must understand that comparing on unexported fields
 // from external packages is not safe since changes in the internal
 // implementation of some external package may cause the result of Equal
 // to unexpectedly change. However, it may be valid to use this option on types
 // defined in an internal package where the semantic meaning of an unexported
 // field is in the control of the user.
 //
 // In many cases, a custom Comparer should be used instead that defines
 // equality as a function of the public API of a type rather than the underlying
 // unexported implementation.
 //
 // For example, the reflect.Type documentation defines equality to be determined
 // by the == operator on the interface (essentially performing a shallow pointer
 // comparison) and most attempts to compare *regexp.Regexp types are interested
 // in only checking that the regular expression strings are equal.
 // Both of these are accomplished using Comparers:
 //
 //	Comparer(func(x, y reflect.Type) bool { return x == y })
 //	Comparer(func(x, y *regexp.Regexp) bool { return x.String() == y.String() })
 //
 // In other cases, the cmpopts.IgnoreUnexported option can be used to ignore
 // all unexported fields on specified struct types.
 func Exporter(f func(reflect.Type) bool) Option {
 	if !supportExporters {
 		panic("Exporter is not supported on purego builds")
 	}
 	return exporter(f)
 }

 type exporter func(reflect.Type) bool

 func (exporter) filter(_ *state, _ reflect.Type, _, _ reflect.Value) applicableOption {
 	panic("not implemented")
 }

 // AllowUnexported returns an Options that allows Equal to forcibly introspect
 // unexported fields of the specified struct types.
 //
 // See Exporter for the proper use of this option.
 func AllowUnexported(types ...interface{}) Option {
 	m := make(map[reflect.Type]bool)
 	for _, typ := range types {
 		t := reflect.TypeOf(typ)
 		if t.Kind() != reflect.Struct {
 			panic(fmt.Sprintf("invalid struct type: %T", typ))
 		}
 		m[t] = true
 	}
 	return exporter(func(t reflect.Type) bool { return m[t] })
 }

 // Result represents the comparison result for a single node and
 // is provided by cmp when calling Result (see Reporter).
 type Result struct {
 	_     [0]func() // Make Result incomparable
 	flags resultFlags
 }

 // Equal reports whether the node was determined to be equal or not.
 // As a special case, ignored nodes are considered equal.
 func (r Result) Equal() bool {
 	return r.flags&(reportEqual|reportByIgnore) != 0
 }

 // ByIgnore reports whether the node is equal because it was ignored.
 // This never reports true if Equal reports false.
 func (r Result) ByIgnore() bool {
 	return r.flags&reportByIgnore != 0
 }

 // ByMethod reports whether the Equal method determined equality.
 func (r Result) ByMethod() bool {
 	return r.flags&reportByMethod != 0
 }

 // ByFunc reports whether a Comparer function determined equality.
 func (r Result) ByFunc() bool {
 	return r.flags&reportByFunc != 0
 }

 // ByCycle reports whether a reference cycle was detected.
 func (r Result) ByCycle() bool {
 	return r.flags&reportByCycle != 0
 }

 type resultFlags uint

 const (
 	_ resultFlags = (1 << iota) / 2

 	reportEqual
 	reportUnequal
 	reportByIgnore
 	reportByMethod
 	reportByFunc
 	reportByCycle
 )

 // Reporter is an Option that can be passed to Equal. When Equal traverses
 // the value trees, it calls PushStep as it descends into each node in the
 // tree and PopStep as it ascend out of the node. The leaves of the tree are
 // either compared (determined to be equal or not equal) or ignored and reported
 // as such by calling the Report method.
 func Reporter(r interface {
 	// PushStep is called when a tree-traversal operation is performed.
 	// The PathStep itself is only valid until the step is popped.
 	// The PathStep.Values are valid for the duration of the entire traversal
 	// and must not be mutated.
 	//
 	// Equal always calls PushStep at the start to provide an operation-less
 	// PathStep used to report the root values.
 	//
 	// Within a slice, the exact set of inserted, removed, or modified elements
 	// is unspecified and may change in future implementations.
 	// The entries of a map are iterated through in an unspecified order.
 	PushStep(PathStep)

 	// Report is called exactly once on leaf nodes to report whether the
 	// comparison identified the node as equal, unequal, or ignored.
 	// A leaf node is one that is immediately preceded by and followed by
 	// a pair of PushStep and PopStep calls.
 	Report(Result)

 	// PopStep ascends back up the value tree.
 	// There is always a matching pop call for every push call.
 	PopStep()
 }) Option {
 	return reporter{r}
 }

 type reporter struct{ reporterIface }
 type reporterIface interface {
 	PushStep(PathStep)
 	Report(Result)
 	PopStep()
 }

 func (reporter) filter(_ *state, _ reflect.Type, _, _ reflect.Value) applicableOption {
 	panic("not implemented")
 }

 // normalizeOption normalizes the input options such that all Options groups
 // are flattened and groups with a single element are reduced to that element.
 // Only coreOptions and Options containing coreOptions are allowed.
 func normalizeOption(src Option) Option {
 	switch opts := flattenOptions(nil, Options{src}); len(opts) {
 	case 0:
 		return nil
 	case 1:
 		return opts[0]
 	default:
 		return opts
 	}
 }

 // flattenOptions copies all options in src to dst as a flat list.
 // Only coreOptions and Options containing coreOptions are allowed.
 func flattenOptions(dst, src Options) Options {
 	for _, opt := range src {
 		switch opt := opt.(type) {
 		case nil:
 			continue
 		case Options:
 			dst = flattenOptions(dst, opt)
 		case coreOption:
 			dst = append(dst, opt)
 		default:
 			panic(fmt.Sprintf("invalid option type: %T", opt))
 		}
 	}
 	return dst
 }
	// 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"
	"regexp"
	"strings"

	"github.com/google/go-cmp/cmp/internal/function"
	)

	// Option configures for specific behavior of Equal and Diff. In particular,
	// the fundamental Option functions (Ignore, Transformer, and Comparer),
	// configure how equality is determined.
	//
	// The fundamental options may be composed with filters (FilterPath and
	// FilterValues) to control the scope over which they are applied.
	//
	// The cmp/cmpopts package provides helper functions for creating options that
	// may be used with Equal and Diff.
	type Option interface {
	// filter applies all filters and returns the option that remains.
	// Each option may only read s.curPath and call s.callTTBFunc.
	//
	// An Options is returned only if multiple comparers or transformers
	// can apply simultaneously and will only contain values of those types
	// or sub-Options containing values of those types.
	filter(s *state, t reflect.Type, vx, vy reflect.Value) applicableOption
	}

	// applicableOption represents the following types:
	// Fundamental: ignore \| validator \| comparer \| transformer
	// Grouping: Options
	type applicableOption interface {
	Option

	// apply executes the option, which may mutate s or panic.
	apply(s *state, vx, vy reflect.Value)
	}

	// coreOption represents the following types:
	// Fundamental: ignore \| validator \| comparer \| transformer
	// Filters: pathFilter \| valuesFilter
	type coreOption interface {
	Option
	isCore()
	}

	type core struct{}

	func (core) isCore() {}

	// Options is a list of Option values that also satisfies the Option interface.
	// Helper comparison packages may return an Options value when packing multiple
	// Option values into a single Option. When this package processes an Options,
	// it will be implicitly expanded into a flat list.
	//
	// Applying a filter on an Options is equivalent to applying that same filter
	// on all individual options held within.
	type Options []Option

	func (opts Options) filter(s *state, t reflect.Type, vx, vy reflect.Value) (out applicableOption) {
	for _, opt := range opts {
	switch opt := opt.filter(s, t, vx, vy); opt.(type) {
	case ignore:
	return ignore{} // Only ignore can short-circuit evaluation
	case validator:
	out = validator{} // Takes precedence over comparer or transformer
	case comparer, transformer, Options:
	switch out.(type) {
	case nil:
	out = opt
	case validator:
	// Keep validator
	case comparer, transformer, Options:
	out = Options{out, opt} // Conflicting comparers or transformers
	}
	}
	}
	return out
	}

	func (opts Options) apply(s *state, _, _ reflect.Value) {
	const warning = "ambiguous set of applicable options"
	const help = "consider using filters to ensure at most one Comparer or Transformer may apply"
	var ss []string
	for _, opt := range flattenOptions(nil, opts) {
	ss = append(ss, fmt.Sprint(opt))
	}
	set := strings.Join(ss, "\n\t")
	panic(fmt.Sprintf("%s at %#v:\n\t%s\n%s", warning, s.curPath, set, help))
	}

	func (opts Options) String() string {
	var ss []string
	for _, opt := range opts {
	ss = append(ss, fmt.Sprint(opt))
	}
	return fmt.Sprintf("Options{%s}", strings.Join(ss, ", "))
	}

	// FilterPath returns a new Option where opt is only evaluated if filter f
	// returns true for the current Path in the value tree.
	//
	// This filter is called even if a slice element or map entry is missing and
	// provides an opportunity to ignore such cases. The filter function must be
	// symmetric such that the filter result is identical regardless of whether the
	// missing value is from x or y.
	//
	// The option passed in may be an Ignore, Transformer, Comparer, Options, or
	// a previously filtered Option.
	func FilterPath(f func(Path) bool, opt Option) Option {
	if f == nil {
	panic("invalid path filter function")
	}
	if opt := normalizeOption(opt); opt != nil {
	return &pathFilter{fnc: f, opt: opt}
	}
	return nil
	}

	type pathFilter struct {
	core
	fnc func(Path) bool
	opt Option
	}

	func (f pathFilter) filter(s *state, t reflect.Type, vx, vy reflect.Value) applicableOption {
	if f.fnc(s.curPath) {
	return f.opt.filter(s, t, vx, vy)
	}
	return nil
	}

	func (f pathFilter) String() string {
	return fmt.Sprintf("FilterPath(%s, %v)", function.NameOf(reflect.ValueOf(f.fnc)), f.opt)
	}

	// FilterValues returns a new Option where opt is only evaluated if filter f,
	// which is a function of the form "func(T, T) bool", returns true for the
	// current pair of values being compared. If either value is invalid or
	// the type of the values is not assignable to T, then this filter implicitly
	// returns false.
	//
	// The filter function must be
	// symmetric (i.e., agnostic to the order of the inputs) and
	// deterministic (i.e., produces the same result when given the same inputs).
	// If T is an interface, it is possible that f is called with two values with
	// different concrete types that both implement T.
	//
	// The option passed in may be an Ignore, Transformer, Comparer, Options, or
	// a previously filtered Option.
	func FilterValues(f interface{}, opt Option) Option {
	v := reflect.ValueOf(f)
	if !function.IsType(v.Type(), function.ValueFilter) \|\| v.IsNil() {
	panic(fmt.Sprintf("invalid values filter function: %T", f))
	}
	if opt := normalizeOption(opt); opt != nil {
	vf := &valuesFilter{fnc: v, opt: opt}
	if ti := v.Type().In(0); ti.Kind() != reflect.Interface \|\| ti.NumMethod() > 0 {
	vf.typ = ti
	}
	return vf
	}
	return nil
	}

	type valuesFilter struct {
	core
	typ reflect.Type // T
	fnc reflect.Value // func(T, T) bool
	opt Option
	}

	func (f valuesFilter) filter(s *state, t reflect.Type, vx, vy reflect.Value) applicableOption {
	if !vx.IsValid() \|\| !vx.CanInterface() \|\| !vy.IsValid() \|\| !vy.CanInterface() {
	return nil
	}
	if (f.typ == nil \|\| t.AssignableTo(f.typ)) && s.callTTBFunc(f.fnc, vx, vy) {
	return f.opt.filter(s, t, vx, vy)
	}
	return nil
	}

	func (f valuesFilter) String() string {
	return fmt.Sprintf("FilterValues(%s, %v)", function.NameOf(f.fnc), f.opt)
	}

	// Ignore is an Option that causes all comparisons to be ignored.
	// This value is intended to be combined with FilterPath or FilterValues.
	// It is an error to pass an unfiltered Ignore option to Equal.
	func Ignore() Option { return ignore{} }

	type ignore struct{ core }

	func (ignore) isFiltered() bool { return false }
	func (ignore) filter(_ *state, _ reflect.Type, _, _ reflect.Value) applicableOption { return ignore{} }
	func (ignore) apply(s *state, _, _ reflect.Value) { s.report(true, reportByIgnore) }
	func (ignore) String() string { return "Ignore()" }

	// validator is a sentinel Option type to indicate that some options could not
	// be evaluated due to unexported fields, missing slice elements, or
	// missing map entries. Both values are validator only for unexported fields.
	type validator struct{ core }

	func (validator) filter(_ *state, _ reflect.Type, vx, vy reflect.Value) applicableOption {
	if !vx.IsValid() \|\| !vy.IsValid() {
	return validator{}
	}
	if !vx.CanInterface() \|\| !vy.CanInterface() {
	return validator{}
	}
	return nil
	}
	func (validator) apply(s *state, vx, vy reflect.Value) {
	// Implies missing slice element or map entry.
	if !vx.IsValid() \|\| !vy.IsValid() {
	s.report(vx.IsValid() == vy.IsValid(), 0)
	return
	}

	// Unable to Interface implies unexported field without visibility access.
	if !vx.CanInterface() \|\| !vy.CanInterface() {
	const help = "consider using a custom Comparer; if you control the implementation of type, you can also consider using an Exporter, AllowUnexported, or cmpopts.IgnoreUnexported"
	var name string
	if t := s.curPath.Index(-2).Type(); t.Name() != "" {
	// Named type with unexported fields.
	name = fmt.Sprintf("%q.%v", t.PkgPath(), t.Name()) // e.g., "path/to/package".MyType
	} else {
	// Unnamed type with unexported fields. Derive PkgPath from field.
	var pkgPath string
	for i := 0; i < t.NumField() && pkgPath == ""; i++ {
	pkgPath = t.Field(i).PkgPath
	}
	name = fmt.Sprintf("%q.(%v)", pkgPath, t.String()) // e.g., "path/to/package".(struct { a int })
	}
	panic(fmt.Sprintf("cannot handle unexported field at %#v:\n\t%v\n%s", s.curPath, name, help))
	}

	panic("not reachable")
	}

	// identRx represents a valid identifier according to the Go specification.
	const identRx = `[_\p{L}][_\p{L}\p{N}]*`

	var identsRx = regexp.MustCompile(`^` + identRx + `(\.` + identRx + `)*$`)

	// Transformer returns an Option that applies a transformation function that
	// converts values of a certain type into that of another.
	//
	// The transformer f must be a function "func(T) R" that converts values of
	// type T to those of type R and is implicitly filtered to input values
	// assignable to T. The transformer must not mutate T in any way.
	//
	// To help prevent some cases of infinite recursive cycles applying the
	// same transform to the output of itself (e.g., in the case where the
	// input and output types are the same), an implicit filter is added such that
	// a transformer is applicable only if that exact transformer is not already
	// in the tail of the Path since the last non-Transform step.
	// For situations where the implicit filter is still insufficient,
	// consider using cmpopts.AcyclicTransformer, which adds a filter
	// to prevent the transformer from being recursively applied upon itself.
	//
	// The name is a user provided label that is used as the Transform.Name in the
	// transformation PathStep (and eventually shown in the Diff output).
	// The name must be a valid identifier or qualified identifier in Go syntax.
	// If empty, an arbitrary name is used.
	func Transformer(name string, f interface{}) Option {
	v := reflect.ValueOf(f)
	if !function.IsType(v.Type(), function.Transformer) \|\| v.IsNil() {
	panic(fmt.Sprintf("invalid transformer function: %T", f))
	}
	if name == "" {
	name = function.NameOf(v)
	if !identsRx.MatchString(name) {
	name = "λ" // Lambda-symbol as placeholder name
	}
	} else if !identsRx.MatchString(name) {
	panic(fmt.Sprintf("invalid name: %q", name))
	}
	tr := &transformer{name: name, fnc: reflect.ValueOf(f)}
	if ti := v.Type().In(0); ti.Kind() != reflect.Interface \|\| ti.NumMethod() > 0 {
	tr.typ = ti
	}
	return tr
	}

	type transformer struct {
	core
	name string
	typ reflect.Type // T
	fnc reflect.Value // func(T) R
	}

	func (tr *transformer) isFiltered() bool { return tr.typ != nil }

	func (tr transformer) filter(s state, t reflect.Type, _, _ reflect.Value) applicableOption {
	for i := len(s.curPath) - 1; i >= 0; i-- {
	if t, ok := s.curPath[i].(Transform); !ok {
	break // Hit most recent non-Transform step
	} else if tr == t.trans {
	return nil // Cannot directly use same Transform
	}
	}
	if tr.typ == nil \|\| t.AssignableTo(tr.typ) {
	return tr
	}
	return nil
	}

	func (tr transformer) apply(s state, vx, vy reflect.Value) {
	step := Transform{&transform{pathStep{typ: tr.fnc.Type().Out(0)}, tr}}
	vvx := s.callTRFunc(tr.fnc, vx, step)
	vvy := s.callTRFunc(tr.fnc, vy, step)
	step.vx, step.vy = vvx, vvy
	s.compareAny(step)
	}

	func (tr transformer) String() string {
	return fmt.Sprintf("Transformer(%s, %s)", tr.name, function.NameOf(tr.fnc))
	}

	// Comparer returns an Option that determines whether two values are equal
	// to each other.
	//
	// The comparer f must be a function "func(T, T) bool" and is implicitly
	// filtered to input values assignable to T. If T is an interface, it is
	// possible that f is called with two values of different concrete types that
	// both implement T.
	//
	// The equality function must be:
	// • Symmetric: equal(x, y) == equal(y, x)
	// • Deterministic: equal(x, y) == equal(x, y)
	// • Pure: equal(x, y) does not modify x or y
	func Comparer(f interface{}) Option {
	v := reflect.ValueOf(f)
	if !function.IsType(v.Type(), function.Equal) \|\| v.IsNil() {
	panic(fmt.Sprintf("invalid comparer function: %T", f))
	}
	cm := &comparer{fnc: v}
	if ti := v.Type().In(0); ti.Kind() != reflect.Interface \|\| ti.NumMethod() > 0 {
	cm.typ = ti
	}
	return cm
	}

	type comparer struct {
	core
	typ reflect.Type // T
	fnc reflect.Value // func(T, T) bool
	}

	func (cm *comparer) isFiltered() bool { return cm.typ != nil }

	func (cm comparer) filter(_ state, t reflect.Type, _, _ reflect.Value) applicableOption {
	if cm.typ == nil \|\| t.AssignableTo(cm.typ) {
	return cm
	}
	return nil
	}

	func (cm comparer) apply(s state, vx, vy reflect.Value) {
	eq := s.callTTBFunc(cm.fnc, vx, vy)
	s.report(eq, reportByFunc)
	}

	func (cm comparer) String() string {
	return fmt.Sprintf("Comparer(%s)", function.NameOf(cm.fnc))
	}

	// Exporter returns an Option that specifies whether Equal is allowed to
	// introspect into the unexported fields of certain struct types.
	//
	// Users of this option must understand that comparing on unexported fields
	// from external packages is not safe since changes in the internal
	// implementation of some external package may cause the result of Equal
	// to unexpectedly change. However, it may be valid to use this option on types
	// defined in an internal package where the semantic meaning of an unexported
	// field is in the control of the user.
	//
	// In many cases, a custom Comparer should be used instead that defines
	// equality as a function of the public API of a type rather than the underlying
	// unexported implementation.
	//
	// For example, the reflect.Type documentation defines equality to be determined
	// by the == operator on the interface (essentially performing a shallow pointer
	// comparison) and most attempts to compare *regexp.Regexp types are interested
	// in only checking that the regular expression strings are equal.
	// Both of these are accomplished using Comparers:
	//
	// Comparer(func(x, y reflect.Type) bool { return x == y })
	// Comparer(func(x, y *regexp.Regexp) bool { return x.String() == y.String() })
	//
	// In other cases, the cmpopts.IgnoreUnexported option can be used to ignore
	// all unexported fields on specified struct types.
	func Exporter(f func(reflect.Type) bool) Option {
	if !supportExporters {
	panic("Exporter is not supported on purego builds")
	}
	return exporter(f)
	}

	type exporter func(reflect.Type) bool

	func (exporter) filter(_ *state, _ reflect.Type, _, _ reflect.Value) applicableOption {
	panic("not implemented")
	}

	// AllowUnexported returns an Options that allows Equal to forcibly introspect
	// unexported fields of the specified struct types.
	//
	// See Exporter for the proper use of this option.
	func AllowUnexported(types ...interface{}) Option {
	m := make(map[reflect.Type]bool)
	for _, typ := range types {
	t := reflect.TypeOf(typ)
	if t.Kind() != reflect.Struct {
	panic(fmt.Sprintf("invalid struct type: %T", typ))
	}
	m[t] = true
	}
	return exporter(func(t reflect.Type) bool { return m[t] })
	}

	// Result represents the comparison result for a single node and
	// is provided by cmp when calling Result (see Reporter).
	type Result struct {
	_ [0]func() // Make Result incomparable
	flags resultFlags
	}

	// Equal reports whether the node was determined to be equal or not.
	// As a special case, ignored nodes are considered equal.
	func (r Result) Equal() bool {
	return r.flags&(reportEqual\|reportByIgnore) != 0
	}

	// ByIgnore reports whether the node is equal because it was ignored.
	// This never reports true if Equal reports false.
	func (r Result) ByIgnore() bool {
	return r.flags&reportByIgnore != 0
	}

	// ByMethod reports whether the Equal method determined equality.
	func (r Result) ByMethod() bool {
	return r.flags&reportByMethod != 0
	}

	// ByFunc reports whether a Comparer function determined equality.
	func (r Result) ByFunc() bool {
	return r.flags&reportByFunc != 0
	}

	// ByCycle reports whether a reference cycle was detected.
	func (r Result) ByCycle() bool {
	return r.flags&reportByCycle != 0
	}

	type resultFlags uint

	const (
	_ resultFlags = (1 << iota) / 2

	reportEqual
	reportUnequal
	reportByIgnore
	reportByMethod
	reportByFunc
	reportByCycle
	)

	// Reporter is an Option that can be passed to Equal. When Equal traverses
	// the value trees, it calls PushStep as it descends into each node in the
	// tree and PopStep as it ascend out of the node. The leaves of the tree are
	// either compared (determined to be equal or not equal) or ignored and reported
	// as such by calling the Report method.
	func Reporter(r interface {
	// PushStep is called when a tree-traversal operation is performed.
	// The PathStep itself is only valid until the step is popped.
	// The PathStep.Values are valid for the duration of the entire traversal
	// and must not be mutated.
	//
	// Equal always calls PushStep at the start to provide an operation-less
	// PathStep used to report the root values.
	//
	// Within a slice, the exact set of inserted, removed, or modified elements
	// is unspecified and may change in future implementations.
	// The entries of a map are iterated through in an unspecified order.
	PushStep(PathStep)

	// Report is called exactly once on leaf nodes to report whether the
	// comparison identified the node as equal, unequal, or ignored.
	// A leaf node is one that is immediately preceded by and followed by
	// a pair of PushStep and PopStep calls.
	Report(Result)

	// PopStep ascends back up the value tree.
	// There is always a matching pop call for every push call.
	PopStep()
	}) Option {
	return reporter{r}
	}

	type reporter struct{ reporterIface }
	type reporterIface interface {
	PushStep(PathStep)
	Report(Result)
	PopStep()
	}

	func (reporter) filter(_ *state, _ reflect.Type, _, _ reflect.Value) applicableOption {
	panic("not implemented")
	}

	// normalizeOption normalizes the input options such that all Options groups
	// are flattened and groups with a single element are reduced to that element.
	// Only coreOptions and Options containing coreOptions are allowed.
	func normalizeOption(src Option) Option {
	switch opts := flattenOptions(nil, Options{src}); len(opts) {
	case 0:
	return nil
	case 1:
	return opts[0]
	default:
	return opts
	}
	}

	// flattenOptions copies all options in src to dst as a flat list.
	// Only coreOptions and Options containing coreOptions are allowed.
	func flattenOptions(dst, src Options) Options {
	for _, opt := range src {
	switch opt := opt.(type) {
	case nil:
	continue
	case Options:
	dst = flattenOptions(dst, opt)
	case coreOption:
	dst = append(dst, opt)
	default:
	panic(fmt.Sprintf("invalid option type: %T", opt))
	}
	}
	return dst
	}