// checkSelection checks that all uses and selections that resolve to
// the specified object would continue to do so after the renaming.
func (r *renamer) checkSelections(from types.Object) {
	for pkg, info := range r.packages {
		if id := someUse(info, from); id != nil {
			if !r.checkExport(id, pkg, from) {
				return
			}
		}

		for syntax, sel := range info.Selections {
			// There may be extant selections of only the old
			// name or only the new name, so we must check both.
			// (If neither, the renaming is sound.)
			//
			// In both cases, we wish to compare the lengths
			// of the implicit field path (Selection.Index)
			// to see if the renaming would change it.
			//
			// If a selection that resolves to 'from', when renamed,
			// would yield a path of the same or shorter length,
			// this indicates ambiguity or a changed referent,
			// analogous to same- or sub-block lexical conflict.
			//
			// If a selection using the name 'to' would
			// yield a path of the same or shorter length,
			// this indicates ambiguity or shadowing,
			// analogous to same- or super-block lexical conflict.

			// TODO(adonovan): fix: derive from Types[syntax.X].Mode
			// TODO(adonovan): test with pointer, value, addressable value.
			isAddressable := true

			if sel.Obj() == from {
				if obj, indices, _ := types.LookupFieldOrMethod(sel.Recv(), isAddressable, from.Pkg(), r.to); obj != nil {
					// Renaming this existing selection of
					// 'from' may block access to an existing
					// type member named 'to'.
					delta := len(indices) - len(sel.Index())
					if delta > 0 {
						continue // no ambiguity
					}
					r.selectionConflict(from, delta, syntax, obj)
					return
				}

			} else if sel.Obj().Name() == r.to {
				if obj, indices, _ := types.LookupFieldOrMethod(sel.Recv(), isAddressable, from.Pkg(), from.Name()); obj == from {
					// Renaming 'from' may cause this existing
					// selection of the name 'to' to change
					// its meaning.
					delta := len(indices) - len(sel.Index())
					if delta > 0 {
						continue //  no ambiguity
					}
					r.selectionConflict(from, -delta, syntax, sel.Obj())
					return
				}
			}
		}
	}
}

// Ident looks up a definition by its import path and identifier names.
//
// buildCtx can be used to control GOPATH, GOOS, GOARCH, build tags,
// and such. If buildCtx is nil, go/build.Default is used.
func Ident(lookup string, buildCtx *build.Context) (*token.Position, error) {
	if buildCtx == nil {
		buildCtx = &build.Default
	}

	importPath, lookup := lookup, ""
	if idx := strings.IndexByte(importPath, '#'); idx >= 0 {
		importPath, lookup = importPath[:idx], importPath[idx+1:]
	}

	idents := strings.Split(lookup, ".")

	fset := token.NewFileSet()
	imp := newImporter(buildCtx, fset)

	pkg, err := imp.Import(importPath)
	if err != nil {
		return nil, fmt.Errorf("cannot import path: %q: %v", importPath, err)
	}

	obj := pkg.Scope().Lookup(idents[0])
	if obj == nil {
		return nil, fmt.Errorf("identifier not found: %q", idents[0])
	}
	for _, name := range idents[1:] {
		obj, _, _ = types.LookupFieldOrMethod(obj.Type(), true, pkg, name)
		if obj == nil {
			return nil, fmt.Errorf("field or method not found: %q", name)
		}
	}
	p := fset.Position(obj.Pos())
	return &p, nil
}

func checkExample(fn *ast.FuncDecl, pkg *Package, report reporter) {
	fnName := fn.Name.Name
	if params := fn.Type.Params; len(params.List) != 0 {
		report("%s should be niladic", fnName)
	}
	if results := fn.Type.Results; results != nil && len(results.List) != 0 {
		report("%s should return nothing", fnName)
	}

	if filesRun && !includesNonTest {
		// The coherence checks between a test and the package it tests
		// will report false positives if no non-test files have
		// been provided.
		return
	}

	if fnName == "Example" {
		// Nothing more to do.
		return
	}

	var (
		exName = strings.TrimPrefix(fnName, "Example")
		elems  = strings.SplitN(exName, "_", 3)
		ident  = elems[0]
		obj    = lookup(ident, extendedScope(pkg))
	)
	if ident != "" && obj == nil {
		// Check ExampleFoo and ExampleBadFoo.
		report("%s refers to unknown identifier: %s", fnName, ident)
		// Abort since obj is absent and no subsequent checks can be performed.
		return
	}
	if len(elems) < 2 {
		// Nothing more to do.
		return
	}

	if ident == "" {
		// Check Example_suffix and Example_BadSuffix.
		if residual := strings.TrimPrefix(exName, "_"); !isExampleSuffix(residual) {
			report("%s has malformed example suffix: %s", fnName, residual)
		}
		return
	}

	mmbr := elems[1]
	if !isExampleSuffix(mmbr) {
		// Check ExampleFoo_Method and ExampleFoo_BadMethod.
		if obj, _, _ := types.LookupFieldOrMethod(obj.Type(), true, obj.Pkg(), mmbr); obj == nil {
			report("%s refers to unknown field or method: %s.%s", fnName, ident, mmbr)
		}
	}
	if len(elems) == 3 && !isExampleSuffix(elems[2]) {
		// Check ExampleFoo_Method_suffix and ExampleFoo_Method_Badsuffix.
		report("%s has malformed example suffix: %s", fnName, elems[2])
	}
}

func ext۰sync۰Pool۰Get(fr *frame, args []value) value {
	Pool := fr.i.prog.ImportedPackage("sync").Type("Pool").Object()
	_, newIndex, _ := types.LookupFieldOrMethod(Pool.Type(), false, Pool.Pkg(), "New")

	if New := (*args[0].(*value)).(structure)[newIndex[0]]; New != nil {
		return call(fr.i, fr, 0, New, nil)
	}
	return nil
}

func (tr *Transformer) matchSelectorExpr(x, y *ast.SelectorExpr) bool {
	if xobj, ok := tr.wildcardObj(x.X); ok {
		field := x.Sel.Name
		yt := tr.info.TypeOf(y.X)
		o, _, _ := types.LookupFieldOrMethod(yt, true, tr.currentPkg, field)
		if o != nil {
			tr.env[xobj.Name()] = y.X // record binding
			return true
		}
	}
	return tr.matchExpr(x.X, y.X)
}

// accessibleFields returns the set of accessible
// field selections on a value of type recv.
func accessibleFields(recv types.Type, from *types.Package) []describeField {
	wantField := func(f *types.Var) bool {
		if !isAccessibleFrom(f, from) {
			return false
		}
		// Check that the field is not shadowed.
		obj, _, _ := types.LookupFieldOrMethod(recv, true, f.Pkg(), f.Name())
		return obj == f
	}

	var fields []describeField
	var visit func(t types.Type, stack []*types.Named)
	visit = func(t types.Type, stack []*types.Named) {
		tStruct, ok := deref(t).Underlying().(*types.Struct)
		if !ok {
			return
		}
	fieldloop:
		for i := 0; i < tStruct.NumFields(); i++ {
			f := tStruct.Field(i)

			// Handle recursion through anonymous fields.
			if f.Anonymous() {
				tf := f.Type()
				if ptr, ok := tf.(*types.Pointer); ok {
					tf = ptr.Elem()
				}
				if named, ok := tf.(*types.Named); ok { // (be defensive)
					// If we've already visited this named type
					// on this path, break the cycle.
					for _, x := range stack {
						if x == named {
							continue fieldloop
						}
					}
					visit(f.Type(), append(stack, named))
				}
			}

			// Save accessible fields.
			if wantField(f) {
				fields = append(fields, describeField{
					implicits: append([]*types.Named(nil), stack...),
					field:     f,
				})
			}
		}
	}
	visit(recv, nil)

	return fields
}

func TestIssue13898(t *testing.T) {
	skipSpecialPlatforms(t)

	// This package only handles gc export data.
	if runtime.Compiler != "gc" {
		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
		return
	}

	// import go/internal/gcimporter which imports go/types partially
	imports := make(map[string]*types.Package)
	_, err := Import(imports, "go/internal/gcimporter", ".")
	if err != nil {
		t.Fatal(err)
	}

	// look for go/types package
	var goTypesPkg *types.Package
	for path, pkg := range imports {
		if path == "go/types" {
			goTypesPkg = pkg
			break
		}
	}
	if goTypesPkg == nil {
		t.Fatal("go/types not found")
	}

	// look for go/types.Object type
	obj := goTypesPkg.Scope().Lookup("Object")
	if obj == nil {
		t.Fatal("go/types.Object not found")
	}
	typ, ok := obj.Type().(*types.Named)
	if !ok {
		t.Fatalf("go/types.Object type is %v; wanted named type", typ)
	}

	// lookup go/types.Object.Pkg method
	m, index, indirect := types.LookupFieldOrMethod(typ, false, nil, "Pkg")
	if m == nil {
		t.Fatalf("go/types.Object.Pkg not found (index = %v, indirect = %v)", index, indirect)
	}

	// the method must belong to go/types
	if m.Pkg().Path() != "go/types" {
		t.Fatalf("found %v; want go/types", m.Pkg())
	}
}

func (p *Package) buildTypes() map[string]*Type {
	if p.Types != nil {
		return p.Types
	}

	p.Types = map[string]*Type{}

	for _, docT := range p.DocPkg.Types {
		name := docT.Name
		if typesT, ok := p.TypesPkg.Scope().Lookup(name).(*types.TypeName); ok {
			funcs := make(map[string]*Func, len(docT.Funcs))
			for _, f := range docT.Funcs {
				funcs[f.Name] = &Func{
					Package: p,
					Doc:     f,
					Types:   p.TypesPkg.Scope().Lookup(f.Name).(*types.Func),
				}
			}

			methods := make(map[string]*Func, len(docT.Methods))
			for _, m := range docT.Methods {
				// Must be found and be *types.Func
				obj, _, _ := types.LookupFieldOrMethod(typesT.Type(), true, p.TypesPkg, m.Name)
				methods[m.Name] = &Func{
					Package: p,
					Doc:     m,
					Types:   obj.(*types.Func),
				}
			}

			p.Types[name] = &Type{
				Package: p,
				Doc:     docT,
				Types:   typesT,
				Funcs:   funcs,
				Methods: methods,
			}
		}
	}

	return p.Types
}

func implements(t types.Type, interfac *types.Interface, pkg *types.Package) bool {
	if interfac == nil || t == nil || interfac.Empty() {
		return false
	}
	if types.Implements(t, interfac) {
		return true
	}
	//For some reason, interfaces that comes
	//already built in (not from sources) are
	//not working with types.Implements method
	for i := 0; i < interfac.NumMethods(); i++ {
		m := interfac.Method(i)
		obj, _, _ := types.LookupFieldOrMethod(t, true, pkg, m.Name())
		if obj == nil {
			util.Debug("method %s not found in type %v", m.Name(), t)
			return false
		}
	}
	return true
}

// On success, findObjects returns the list of objects named
// spec.fromName matching the spec.  On success, the result has exactly
// one element unless spec.searchFor!="", in which case it has at least one
// element.
//
func findObjects(info *loader.PackageInfo, spec *spec) ([]types.Object, error) {
	if spec.pkgMember == "" {
		if spec.searchFor == "" {
			panic(spec)
		}
		objects := searchDefs(&info.Info, spec.searchFor)
		if objects == nil {
			return nil, fmt.Errorf("no object %q declared in package %q",
				spec.searchFor, info.Pkg.Path())
		}
		return objects, nil
	}

	pkgMember := info.Pkg.Scope().Lookup(spec.pkgMember)
	if pkgMember == nil {
		return nil, fmt.Errorf("package %q has no member %q",
			info.Pkg.Path(), spec.pkgMember)
	}

	var searchFunc *types.Func
	if spec.typeMember == "" {
		// package member
		if spec.searchFor == "" {
			return []types.Object{pkgMember}, nil
		}

		// Search within pkgMember, which must be a function.
		searchFunc, _ = pkgMember.(*types.Func)
		if searchFunc == nil {
			return nil, fmt.Errorf("cannot search for %q within %s %q",
				spec.searchFor, objectKind(pkgMember), pkgMember)
		}
	} else {
		// field/method of type
		// e.g. (encoding/json.Decoder).Decode
		// or ::x within it.

		tName, _ := pkgMember.(*types.TypeName)
		if tName == nil {
			return nil, fmt.Errorf("%s.%s is a %s, not a type",
				info.Pkg.Path(), pkgMember.Name(), objectKind(pkgMember))
		}

		// search within named type.
		obj, _, _ := types.LookupFieldOrMethod(tName.Type(), true, info.Pkg, spec.typeMember)
		if obj == nil {
			return nil, fmt.Errorf("cannot find field or method %q of %s %s.%s",
				spec.typeMember, typeKind(tName.Type()), info.Pkg.Path(), tName.Name())
		}

		if spec.searchFor == "" {
			// If it is an embedded field, return the type of the field.
			if v, ok := obj.(*types.Var); ok && v.Anonymous() {
				switch t := v.Type().(type) {
				case *types.Pointer:
					return []types.Object{t.Elem().(*types.Named).Obj()}, nil
				case *types.Named:
					return []types.Object{t.Obj()}, nil
				}
			}
			return []types.Object{obj}, nil
		}

		searchFunc, _ = obj.(*types.Func)
		if searchFunc == nil {
			return nil, fmt.Errorf("cannot search for local name %q within %s (%s.%s).%s; need a function",
				spec.searchFor, objectKind(obj), info.Pkg.Path(), tName.Name(),
				obj.Name())
		}
		if isInterface(tName.Type()) {
			return nil, fmt.Errorf("cannot search for local name %q within abstract method (%s.%s).%s",
				spec.searchFor, info.Pkg.Path(), tName.Name(), searchFunc.Name())
		}
	}

	// -- search within function or method --

	decl := funcDecl(info, searchFunc)
	if decl == nil {
		return nil, fmt.Errorf("cannot find syntax for %s", searchFunc) // can't happen?
	}

	var objects []types.Object
	for _, obj := range searchDefs(&info.Info, spec.searchFor) {
		// We use positions, not scopes, to determine whether
		// the obj is within searchFunc.  This is clumsy, but the
		// alternative, using the types.Scope tree, doesn't
		// account for non-lexical objects like fields and
		// interface methods.
		if decl.Pos() <= obj.Pos() && obj.Pos() < decl.End() && obj != searchFunc {
			objects = append(objects, obj)
		}
	}
	if objects == nil {
		return nil, fmt.Errorf("no local definition of %q within %s",
//.........这里部分代码省略.........

//buildQueryStrings build names for matching
//if onlyExport it's true only query Exported identifier else only Unexported
func buildQueryStrings(queries chan *queryIdent, pkg *types.Package, info *types.Info, onlyExport bool) {
	defer close(queries)

	var typesDefs []types.Object
	typesByField := make(map[types.Object]types.Object)
	interfaceByMethod := make(map[types.Object]types.Object)

	//get definition of types first
	for ident, obj := range info.Defs {
		if obj == nil {
			continue
		}

		if ident.IsExported() != onlyExport {
			//querying unexport, so we need save typesDefs for finding fields func etc..
			if !onlyExport {
				typesDefs = append(typesDefs, obj)
			}
			continue
		}

		switch obj.(type) {
		case *types.TypeName:
			var typeOfObj string
			switch t := obj.Type().Underlying().(type) {
			case *types.Struct:
				for i := 0; i < t.NumFields(); i++ {
					field := t.Field(i)
					typesByField[field] = obj
				}
				typeOfObj = "@struct"
			case *types.Interface:
				for i := 0; i < t.NumMethods(); i++ {
					method := t.Method(i)
					interfaceByMethod[method] = obj
				}
				for i := 0; i < t.NumExplicitMethods(); i++ {
					method := t.ExplicitMethod(i)
					interfaceByMethod[method] = obj
				}
				typeOfObj = "@interface"
			default:
				typeOfObj = "@type"
			}
			query := pkg.Name() + "." + nameExported(obj.Name()) + typeOfObj
			queries <- &queryIdent{query, ident}
			typesDefs = append(typesDefs, obj)
		}
	}

	//get rest of definitions
	for ident, obj := range info.Defs {
		if obj == nil {
			continue
		}
		if ident.IsExported() != onlyExport {
			continue
		}

		if sobj, ok := typesByField[obj]; ok {
			queries <- &queryIdent{joinQuery(pkg, sobj, obj, "@attr"), ident}
		} else if sobj, ok := interfaceByMethod[obj]; ok {
			queries <- &queryIdent{joinQuery(pkg, sobj, obj, "@method"), ident}
		} else {

			switch t := obj.(type) {
			case *types.Const:
				queries <- &queryIdent{joinQuery(pkg, nil, obj, "@const"), ident}
			case *types.Var:
				if !t.IsField() {
					queries <- &queryIdent{joinQuery(pkg, nil, obj, "@var"), ident}
				}
			case *types.Func:
				foundLikeMethod := false
				for _, tobj := range typesDefs {
					tfield, _, _ := types.LookupFieldOrMethod(tobj.Type(), true, pkg, obj.Name())
					if tfield == nil {
						continue
					}
					if tfield.Pos() == obj.Pos() {
						queries <- &queryIdent{joinQuery(pkg, tobj, tfield, "@method"), ident}
						foundLikeMethod = true
					}
				}
				if !foundLikeMethod {
					queries <- &queryIdent{joinQuery(pkg, nil, obj, "@func"), ident}

				}
			default:
			}
		}

	}

}

// hasMethod reports whether the type contains a method with the given name.
// It is part of the workaround for Formatters and should be deleted when
// that workaround is no longer necessary.
// TODO: This could be better once issue 6259 is fixed.
func (f *File) hasMethod(typ types.Type, name string) bool {
	// assume we have an addressable variable of type typ
	obj, _, _ := types.LookupFieldOrMethod(typ, true, f.pkg.typesPkg, name)
	_, ok := obj.(*types.Func)
	return ok
}

func main() {
	flag.Parse()
	exitStatus := 0
	importPaths := gotool.ImportPaths(flag.Args())
	if len(importPaths) == 0 {
		importPaths = []string{"."}
	}
	ctx := build.Default
	for _, pkgPath := range importPaths {
		visitor := &visitor{
			m:    make(map[types.Type]map[string]int),
			skip: make(map[types.Type]struct{}),
		}
		loadcfg := loader.Config{
			Build: &ctx,
		}
		rest, err := loadcfg.FromArgs([]string{pkgPath}, *loadTestFiles)
		if err != nil {
			fmt.Fprintf(os.Stderr, "could not parse arguments: %s", err)
			continue
		}
		if len(rest) > 0 {
			fmt.Fprintf(os.Stderr, "unhandled extra arguments: %v", rest)
			continue
		}

		program, err := loadcfg.Load()
		if err != nil {
			fmt.Fprintf(os.Stderr, "could not type check: %s", err)
			continue
		}

		pkg := program.InitialPackages()[0]
		visitor.prog = program
		visitor.pkg = pkg
		for _, f := range pkg.Files {
			ast.Walk(visitor, f)
		}

		for t := range visitor.m {
			if _, skip := visitor.skip[t]; skip {
				continue
			}
			for fieldName, v := range visitor.m[t] {
				if !*reportExported && ast.IsExported(fieldName) {
					continue
				}
				if v == 0 {
					field, _, _ := types.LookupFieldOrMethod(t, false, pkg.Pkg, fieldName)
					if fieldName == "XMLName" {
						if named, ok := field.Type().(*types.Named); ok && named.Obj().Pkg().Path() == "encoding/xml" {
							continue
						}
					}
					pos := program.Fset.Position(field.Pos())
					fmt.Printf("%s: %s:%d:%d: %s.%s\n",
						pkgPath, pos.Filename, pos.Line, pos.Column,
						types.TypeString(t, nil), fieldName,
					)
					exitStatus = 1
				}
			}
		}
	}
	os.Exit(exitStatus)
}

// checkMethod performs safety checks for renaming a method.
// There are three hazards:
// - declaration conflicts
// - selection ambiguity/changes
// - entailed renamings of assignable concrete/interface types.
//   We reject renamings initiated at concrete methods if it would
//   change the assignability relation.  For renamings of abstract
//   methods, we rename all methods transitively coupled to it via
//   assignability.
func (r *renamer) checkMethod(from *types.Func) {
	// e.g. error.Error
	if from.Pkg() == nil {
		r.errorf(from.Pos(), "you cannot rename built-in method %s", from)
		return
	}

	// ASSIGNABILITY: We reject renamings of concrete methods that
	// would break a 'satisfy' constraint; but renamings of abstract
	// methods are allowed to proceed, and we rename affected
	// concrete and abstract methods as necessary.  It is the
	// initial method that determines the policy.

	// Check for conflict at point of declaration.
	// Check to ensure preservation of assignability requirements.
	R := recv(from).Type()
	if isInterface(R) {
		// Abstract method

		// declaration
		prev, _, _ := types.LookupFieldOrMethod(R, false, from.Pkg(), r.to)
		if prev != nil {
			r.errorf(from.Pos(), "renaming this interface method %q to %q",
				from.Name(), r.to)
			r.errorf(prev.Pos(), "\twould conflict with this method")
			return
		}

		// Check all interfaces that embed this one for
		// declaration conflicts too.
		for _, info := range r.packages {
			// Start with named interface types (better errors)
			for _, obj := range info.Defs {
				if obj, ok := obj.(*types.TypeName); ok && isInterface(obj.Type()) {
					f, _, _ := types.LookupFieldOrMethod(
						obj.Type(), false, from.Pkg(), from.Name())
					if f == nil {
						continue
					}
					t, _, _ := types.LookupFieldOrMethod(
						obj.Type(), false, from.Pkg(), r.to)
					if t == nil {
						continue
					}
					r.errorf(from.Pos(), "renaming this interface method %q to %q",
						from.Name(), r.to)
					r.errorf(t.Pos(), "\twould conflict with this method")
					r.errorf(obj.Pos(), "\tin named interface type %q", obj.Name())
				}
			}

			// Now look at all literal interface types (includes named ones again).
			for e, tv := range info.Types {
				if e, ok := e.(*ast.InterfaceType); ok {
					_ = e
					_ = tv.Type.(*types.Interface)
					// TODO(adonovan): implement same check as above.
				}
			}
		}

		// assignability
		//
		// Find the set of concrete or abstract methods directly
		// coupled to abstract method 'from' by some
		// satisfy.Constraint, and rename them too.
		for key := range r.satisfy() {
			// key = (lhs, rhs) where lhs is always an interface.

			lsel := r.msets.MethodSet(key.LHS).Lookup(from.Pkg(), from.Name())
			if lsel == nil {
				continue
			}
			rmethods := r.msets.MethodSet(key.RHS)
			rsel := rmethods.Lookup(from.Pkg(), from.Name())
			if rsel == nil {
				continue
			}

			// If both sides have a method of this name,
			// and one of them is m, the other must be coupled.
			var coupled *types.Func
			switch from {
			case lsel.Obj():
				coupled = rsel.Obj().(*types.Func)
			case rsel.Obj():
				coupled = lsel.Obj().(*types.Func)
			default:
				continue
			}

//.........这里部分代码省略.........

// checkStructField checks that the field renaming will not cause
// conflicts at its declaration, or ambiguity or changes to any selection.
func (r *renamer) checkStructField(from *types.Var) {
	// Check that the struct declaration is free of field conflicts,
	// and field/method conflicts.

	// go/types offers no easy way to get from a field (or interface
	// method) to its declaring struct (or interface), so we must
	// ascend the AST.
	info, path, _ := r.iprog.PathEnclosingInterval(from.Pos(), from.Pos())
	// path matches this pattern:
	// [Ident SelectorExpr? StarExpr? Field FieldList StructType ParenExpr* ... File]

	// Ascend to FieldList.
	var i int
	for {
		if _, ok := path[i].(*ast.FieldList); ok {
			break
		}
		i++
	}
	i++
	tStruct := path[i].(*ast.StructType)
	i++
	// Ascend past parens (unlikely).
	for {
		_, ok := path[i].(*ast.ParenExpr)
		if !ok {
			break
		}
		i++
	}
	if spec, ok := path[i].(*ast.TypeSpec); ok {
		// This struct is also a named type.
		// We must check for direct (non-promoted) field/field
		// and method/field conflicts.
		named := info.Defs[spec.Name].Type()
		prev, indices, _ := types.LookupFieldOrMethod(named, true, info.Pkg, r.to)
		if len(indices) == 1 {
			r.errorf(from.Pos(), "renaming this field %q to %q",
				from.Name(), r.to)
			r.errorf(prev.Pos(), "\twould conflict with this %s",
				objectKind(prev))
			return // skip checkSelections to avoid redundant errors
		}
	} else {
		// This struct is not a named type.
		// We need only check for direct (non-promoted) field/field conflicts.
		T := info.Types[tStruct].Type.Underlying().(*types.Struct)
		for i := 0; i < T.NumFields(); i++ {
			if prev := T.Field(i); prev.Name() == r.to {
				r.errorf(from.Pos(), "renaming this field %q to %q",
					from.Name(), r.to)
				r.errorf(prev.Pos(), "\twould conflict with this field")
				return // skip checkSelections to avoid redundant errors
			}
		}
	}

	// Renaming an anonymous field requires renaming the type too. e.g.
	// 	print(s.T)       // if we rename T to U,
	// 	type T int       // this and
	// 	var s struct {T} // this must change too.
	if from.Anonymous() {
		if named, ok := from.Type().(*types.Named); ok {
			r.check(named.Obj())
		} else if named, ok := deref(from.Type()).(*types.Named); ok {
			r.check(named.Obj())
		}
	}

	// Check integrity of existing (field and method) selections.
	r.checkSelections(from)
}

// checkExample walks the documentation example functions checking for common
// mistakes of misnamed functions, failure to map functions to existing
// identifiers, etc.
func checkExample(f *File, node ast.Node) {
	if !strings.HasSuffix(f.name, "_test.go") {
		return
	}
	var (
		pkg     = f.pkg
		pkgName = pkg.typesPkg.Name()
		scopes  = []*types.Scope{pkg.typesPkg.Scope()}
		lookup  = func(name string) types.Object {
			for _, scope := range scopes {
				if o := scope.Lookup(name); o != nil {
					return o
				}
			}
			return nil
		}
	)
	if strings.HasSuffix(pkgName, "_test") {
		// Treat 'package foo_test' as an alias for 'package foo'.
		var (
			basePkg = strings.TrimSuffix(pkgName, "_test")
			pkg     = f.pkg
		)
		for _, p := range pkg.typesPkg.Imports() {
			if p.Name() == basePkg {
				scopes = append(scopes, p.Scope())
				break
			}
		}
	}
	fn, ok := node.(*ast.FuncDecl)
	if !ok {
		// Ignore non-functions.
		return
	}
	var (
		fnName = fn.Name.Name
		report = func(format string, args ...interface{}) { f.Badf(node.Pos(), format, args...) }
	)
	if fn.Recv != nil || !strings.HasPrefix(fnName, "Example") {
		// Ignore methods and types not named "Example".
		return
	}
	if params := fn.Type.Params; len(params.List) != 0 {
		report("%s should be niladic", fnName)
	}
	if results := fn.Type.Results; results != nil && len(results.List) != 0 {
		report("%s should return nothing", fnName)
	}
	if fnName == "Example" {
		// Nothing more to do.
		return
	}
	if filesRun && !includesNonTest {
		// The coherence checks between a test and the package it tests
		// will report false positives if no non-test files have
		// been provided.
		return
	}
	var (
		exName = strings.TrimPrefix(fnName, "Example")
		elems  = strings.SplitN(exName, "_", 3)
		ident  = elems[0]
		obj    = lookup(ident)
	)
	if ident != "" && obj == nil {
		// Check ExampleFoo and ExampleBadFoo.
		report("%s refers to unknown identifier: %s", fnName, ident)
		// Abort since obj is absent and no subsequent checks can be performed.
		return
	}
	if elemCnt := strings.Count(exName, "_"); elemCnt == 0 {
		// Nothing more to do.
		return
	}
	mmbr := elems[1]
	if ident == "" {
		// Check Example_suffix and Example_BadSuffix.
		if residual := strings.TrimPrefix(exName, "_"); !isExampleSuffix(residual) {
			report("%s has malformed example suffix: %s", fnName, residual)
		}
		return
	}
	if !isExampleSuffix(mmbr) {
		// Check ExampleFoo_Method and ExampleFoo_BadMethod.
		if obj, _, _ := types.LookupFieldOrMethod(obj.Type(), true, obj.Pkg(), mmbr); obj == nil {
			report("%s refers to unknown field or method: %s.%s", fnName, ident, mmbr)
		}
	}
	if len(elems) == 3 && !isExampleSuffix(elems[2]) {
		// Check ExampleFoo_Method_suffix and ExampleFoo_Method_Badsuffix.
		report("%s has malformed example suffix: %s", fnName, elems[2])
	}
	return
}