internal/lsp/source/implementation.go - tools - Git at Google

 // 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 file.

 package source

 import (
 	"context"
 	"errors"
 	"fmt"
 	"go/ast"
 	"go/token"
 	"go/types"
 	"sort"

 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/span"
 	"golang.org/x/xerrors"
 )

 func Implementation(ctx context.Context, snapshot Snapshot, f FileHandle, pp protocol.Position) ([]protocol.Location, error) {
 	ctx, done := event.Start(ctx, "source.Implementation")
 	defer done()

 	impls, err := implementations(ctx, snapshot, f, pp)
 	if err != nil {
 		return nil, err
 	}
 	var locations []protocol.Location
 	for _, impl := range impls {
 		if impl.pkg == nil || len(impl.pkg.CompiledGoFiles()) == 0 {
 			continue
 		}
 		rng, err := objToMappedRange(snapshot, impl.pkg, impl.obj)
 		if err != nil {
 			return nil, err
 		}
 		pr, err := rng.Range()
 		if err != nil {
 			return nil, err
 		}
 		locations = append(locations, protocol.Location{
 			URI:   protocol.URIFromSpanURI(rng.URI()),
 			Range: pr,
 		})
 	}
 	sort.Slice(locations, func(i, j int) bool {
 		li, lj := locations[i], locations[j]
 		if li.URI == lj.URI {
 			return protocol.CompareRange(li.Range, lj.Range) < 0
 		}
 		return li.URI < lj.URI
 	})
 	return locations, nil
 }

 var ErrNotAType = errors.New("not a type name or method")

 // implementations returns the concrete implementations of the specified
 // interface, or the interfaces implemented by the specified concrete type.
 func implementations(ctx context.Context, s Snapshot, f FileHandle, pp protocol.Position) ([]qualifiedObject, error) {
 	var (
 		impls []qualifiedObject
 		seen  = make(map[token.Position]bool)
 		fset  = s.FileSet()
 	)

 	qos, err := qualifiedObjsAtProtocolPos(ctx, s, f.URI(), pp)
 	if err != nil {
 		return nil, err
 	}
 	for _, qo := range qos {
 		var (
 			queryType   types.Type
 			queryMethod *types.Func
 		)

 		switch obj := qo.obj.(type) {
 		case *types.Func:
 			queryMethod = obj
 			if recv := obj.Type().(*types.Signature).Recv(); recv != nil {
 				queryType = ensurePointer(recv.Type())
 			}
 		case *types.TypeName:
 			queryType = ensurePointer(obj.Type())
 		}

 		if queryType == nil {
 			return nil, ErrNotAType
 		}

 		if types.NewMethodSet(queryType).Len() == 0 {
 			return nil, nil
 		}

 		// Find all named types, even local types (which can have methods
 		// due to promotion).
 		var (
 			allNamed []*types.Named
 			pkgs     = make(map[*types.Package]Package)
 		)
 		knownPkgs, err := s.KnownPackages(ctx)
 		if err != nil {
 			return nil, err
 		}
 		for _, pkg := range knownPkgs {
 			pkgs[pkg.GetTypes()] = pkg
 			info := pkg.GetTypesInfo()
 			for _, obj := range info.Defs {
 				obj, ok := obj.(*types.TypeName)
 				// We ignore aliases 'type M = N' to avoid duplicate reporting
 				// of the Named type N.
 				if !ok || obj.IsAlias() {
 					continue
 				}
 				if named, ok := obj.Type().(*types.Named); ok {
 					allNamed = append(allNamed, named)
 				}
 			}
 		}

 		// Find all the named types that match our query.
 		for _, named := range allNamed {
 			var (
 				candObj  types.Object = named.Obj()
 				candType              = ensurePointer(named)
 			)

 			if !concreteImplementsIntf(candType, queryType) {
 				continue
 			}

 			ms := types.NewMethodSet(candType)
 			if ms.Len() == 0 {
 				// Skip empty interfaces.
 				continue
 			}

 			// If client queried a method, look up corresponding candType method.
 			if queryMethod != nil {
 				sel := ms.Lookup(queryMethod.Pkg(), queryMethod.Name())
 				if sel == nil {
 					continue
 				}
 				candObj = sel.Obj()
 			}

 			pos := fset.Position(candObj.Pos())
 			if candObj == queryMethod || seen[pos] {
 				continue
 			}

 			seen[pos] = true

 			impls = append(impls, qualifiedObject{
 				obj: candObj,
 				pkg: pkgs[candObj.Pkg()],
 			})
 		}
 	}

 	return impls, nil
 }

 // concreteImplementsIntf returns true if a is an interface type implemented by
 // concrete type b, or vice versa.
 func concreteImplementsIntf(a, b types.Type) bool {
 	aIsIntf, bIsIntf := IsInterface(a), IsInterface(b)

 	// Make sure exactly one is an interface type.
 	if aIsIntf == bIsIntf {
 		return false
 	}

 	// Rearrange if needed so "a" is the concrete type.
 	if aIsIntf {
 		a, b = b, a
 	}

 	return types.AssignableTo(a, b)
 }

 // ensurePointer wraps T in a *types.Pointer if T is a named, non-interface
 // type. This is useful to make sure you consider a named type's full method
 // set.
 func ensurePointer(T types.Type) types.Type {
 	if _, ok := T.(*types.Named); ok && !IsInterface(T) {
 		return types.NewPointer(T)
 	}

 	return T
 }

 type qualifiedObject struct {
 	obj types.Object

 	// pkg is the Package that contains obj's definition.
 	pkg Package

 	// node is the *ast.Ident or *ast.ImportSpec we followed to find obj, if any.
 	node ast.Node

 	// sourcePkg is the Package that contains node, if any.
 	sourcePkg Package
 }

 var (
 	errBuiltin       = errors.New("builtin object")
 	errNoObjectFound = errors.New("no object found")
 )

 // qualifiedObjsAtProtocolPos returns info for all the type.Objects
 // referenced at the given position. An object will be returned for
 // every package that the file belongs to, in every typechecking mode
 // applicable.
 func qualifiedObjsAtProtocolPos(ctx context.Context, s Snapshot, uri span.URI, pp protocol.Position) ([]qualifiedObject, error) {
 	pkgs, err := s.PackagesForFile(ctx, uri, TypecheckAll)
 	if err != nil {
 		return nil, err
 	}
 	if len(pkgs) == 0 {
 		return nil, errNoObjectFound
 	}
 	pkg := pkgs[0]
 	var offset int
 	pgf, err := pkg.File(uri)
 	if err != nil {
 		return nil, err
 	}
 	spn, err := pgf.Mapper.PointSpan(pp)
 	if err != nil {
 		return nil, err
 	}
 	rng, err := spn.Range(pgf.Mapper.Converter)
 	if err != nil {
 		return nil, err
 	}
 	offset = pgf.Tok.Offset(rng.Start)
 	return qualifiedObjsAtLocation(ctx, s, objSearchKey{uri, offset}, map[objSearchKey]bool{})
 }

 type objSearchKey struct {
 	uri    span.URI
 	offset int
 }

 // qualifiedObjsAtLocation finds all objects referenced at offset in uri, across
 // all packages in the snapshot.
 func qualifiedObjsAtLocation(ctx context.Context, s Snapshot, key objSearchKey, seen map[objSearchKey]bool) ([]qualifiedObject, error) {
 	if seen[key] {
 		return nil, nil
 	}
 	seen[key] = true

 	// We search for referenced objects starting with all packages containing the
 	// current location, and then repeating the search for every distinct object
 	// location discovered.
 	//
 	// In the common case, there should be at most one additional location to
 	// consider: the definition of the object referenced by the location. But we
 	// try to be comprehensive in case we ever support variations on build
 	// constraints.

 	pkgs, err := s.PackagesForFile(ctx, key.uri, TypecheckAll)
 	if err != nil {
 		return nil, err
 	}

 	// report objects in the order we encounter them. This ensures that the first
 	// result is at the cursor...
 	var qualifiedObjs []qualifiedObject
 	// ...but avoid duplicates.
 	seenObjs := map[types.Object]bool{}

 	for _, searchpkg := range pkgs {
 		pgf, err := searchpkg.File(key.uri)
 		if err != nil {
 			return nil, err
 		}
 		pos := pgf.Tok.Pos(key.offset)
 		path := pathEnclosingObjNode(pgf.File, pos)
 		if path == nil {
 			continue
 		}
 		var objs []types.Object
 		switch leaf := path[0].(type) {
 		case *ast.Ident:
 			// If leaf represents an implicit type switch object or the type
 			// switch "assign" variable, expand to all of the type switch's
 			// implicit objects.
 			if implicits, _ := typeSwitchImplicits(searchpkg, path); len(implicits) > 0 {
 				objs = append(objs, implicits...)
 			} else {
 				obj := searchpkg.GetTypesInfo().ObjectOf(leaf)
 				if obj == nil {
 					return nil, xerrors.Errorf("%w for %q", errNoObjectFound, leaf.Name)
 				}
 				objs = append(objs, obj)
 			}
 		case *ast.ImportSpec:
 			// Look up the implicit *types.PkgName.
 			obj := searchpkg.GetTypesInfo().Implicits[leaf]
 			if obj == nil {
 				return nil, xerrors.Errorf("%w for import %q", errNoObjectFound, ImportPath(leaf))
 			}
 			objs = append(objs, obj)
 		}
 		// Get all of the transitive dependencies of the search package.
 		pkgs := make(map[*types.Package]Package)
 		var addPkg func(pkg Package)
 		addPkg = func(pkg Package) {
 			pkgs[pkg.GetTypes()] = pkg
 			for _, imp := range pkg.Imports() {
 				if _, ok := pkgs[imp.GetTypes()]; !ok {
 					addPkg(imp)
 				}
 			}
 		}
 		addPkg(searchpkg)
 		for _, obj := range objs {
 			if obj.Parent() == types.Universe {
 				return nil, xerrors.Errorf("%q: %w", obj.Name(), errBuiltin)
 			}
 			pkg, ok := pkgs[obj.Pkg()]
 			if !ok {
 				event.Error(ctx, fmt.Sprintf("no package for obj %s: %v", obj, obj.Pkg()), err)
 				continue
 			}
 			qualifiedObjs = append(qualifiedObjs, qualifiedObject{
 				obj:       obj,
 				pkg:       pkg,
 				sourcePkg: searchpkg,
 				node:      path[0],
 			})
 			seenObjs[obj] = true

 			// If the qualified object is in another file (or more likely, another
 			// package), it's possible that there is another copy of it in a package
 			// that we haven't searched, e.g. a test variant. See golang/go#47564.
 			//
 			// In order to be sure we've considered all packages, call
 			// qualifiedObjsAtLocation recursively for all locations we encounter. We
 			// could probably be more precise here, only continuing the search if obj
 			// is in another package, but this should be good enough to find all
 			// uses.

 			pos := obj.Pos()
 			var uri span.URI
 			offset := -1
 			for _, pgf := range pkg.CompiledGoFiles() {
 				if pgf.Tok.Base() <= int(pos) && int(pos) <= pgf.Tok.Base()+pgf.Tok.Size() {
 					offset = pgf.Tok.Offset(pos)
 					uri = pgf.URI
 				}
 			}
 			if offset >= 0 {
 				otherObjs, err := qualifiedObjsAtLocation(ctx, s, objSearchKey{uri, offset}, seen)
 				if err != nil {
 					return nil, err
 				}
 				for _, other := range otherObjs {
 					if !seenObjs[other.obj] {
 						qualifiedObjs = append(qualifiedObjs, other)
 						seenObjs[other.obj] = true
 					}
 				}
 			} else {
 				return nil, fmt.Errorf("missing file for position of %q in %q", obj.Name(), obj.Pkg().Name())
 			}
 		}
 	}
 	// Return an error if no objects were found since callers will assume that
 	// the slice has at least 1 element.
 	if len(qualifiedObjs) == 0 {
 		return nil, errNoObjectFound
 	}
 	return qualifiedObjs, nil
 }

 // pathEnclosingObjNode returns the AST path to the object-defining
 // node associated with pos. "Object-defining" means either an
 // *ast.Ident mapped directly to a types.Object or an ast.Node mapped
 // implicitly to a types.Object.
 func pathEnclosingObjNode(f *ast.File, pos token.Pos) []ast.Node {
 	var (
 		path  []ast.Node
 		found bool
 	)

 	ast.Inspect(f, func(n ast.Node) bool {
 		if found {
 			return false
 		}

 		if n == nil {
 			path = path[:len(path)-1]
 			return false
 		}

 		path = append(path, n)

 		switch n := n.(type) {
 		case *ast.Ident:
 			// Include the position directly after identifier. This handles
 			// the common case where the cursor is right after the
 			// identifier the user is currently typing. Previously we
 			// handled this by calling astutil.PathEnclosingInterval twice,
 			// once for "pos" and once for "pos-1".
 			found = n.Pos() <= pos && pos <= n.End()
 		case *ast.ImportSpec:
 			if n.Path.Pos() <= pos && pos < n.Path.End() {
 				found = true
 				// If import spec has a name, add name to path even though
 				// position isn't in the name.
 				if n.Name != nil {
 					path = append(path, n.Name)
 				}
 			}
 		case *ast.StarExpr:
 			// Follow star expressions to the inner identifier.
 			if pos == n.Star {
 				pos = n.X.Pos()
 			}
 		}

 		return !found
 	})

 	if len(path) == 0 {
 		return nil
 	}

 	// Reverse path so leaf is first element.
 	for i := 0; i < len(path)/2; i++ {
 		path[i], path[len(path)-1-i] = path[len(path)-1-i], path[i]
 	}

 	return path
 }
	// 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 file.

	package source

	import (
	"context"
	"errors"
	"fmt"
	"go/ast"
	"go/token"
	"go/types"
	"sort"

	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/lsp/protocol"
	"golang.org/x/tools/internal/span"
	"golang.org/x/xerrors"
	)

	func Implementation(ctx context.Context, snapshot Snapshot, f FileHandle, pp protocol.Position) ([]protocol.Location, error) {
	ctx, done := event.Start(ctx, "source.Implementation")
	defer done()

	impls, err := implementations(ctx, snapshot, f, pp)
	if err != nil {
	return nil, err
	}
	var locations []protocol.Location
	for _, impl := range impls {
	if impl.pkg == nil \|\| len(impl.pkg.CompiledGoFiles()) == 0 {
	continue
	}
	rng, err := objToMappedRange(snapshot, impl.pkg, impl.obj)
	if err != nil {
	return nil, err
	}
	pr, err := rng.Range()
	if err != nil {
	return nil, err
	}
	locations = append(locations, protocol.Location{
	URI: protocol.URIFromSpanURI(rng.URI()),
	Range: pr,
	})
	}
	sort.Slice(locations, func(i, j int) bool {
	li, lj := locations[i], locations[j]
	if li.URI == lj.URI {
	return protocol.CompareRange(li.Range, lj.Range) < 0
	}
	return li.URI < lj.URI
	})
	return locations, nil
	}

	var ErrNotAType = errors.New("not a type name or method")

	// implementations returns the concrete implementations of the specified
	// interface, or the interfaces implemented by the specified concrete type.
	func implementations(ctx context.Context, s Snapshot, f FileHandle, pp protocol.Position) ([]qualifiedObject, error) {
	var (
	impls []qualifiedObject
	seen = make(map[token.Position]bool)
	fset = s.FileSet()
	)

	qos, err := qualifiedObjsAtProtocolPos(ctx, s, f.URI(), pp)
	if err != nil {
	return nil, err
	}
	for _, qo := range qos {
	var (
	queryType types.Type
	queryMethod *types.Func
	)

	switch obj := qo.obj.(type) {
	case *types.Func:
	queryMethod = obj
	if recv := obj.Type().(*types.Signature).Recv(); recv != nil {
	queryType = ensurePointer(recv.Type())
	}
	case *types.TypeName:
	queryType = ensurePointer(obj.Type())
	}

	if queryType == nil {
	return nil, ErrNotAType
	}

	if types.NewMethodSet(queryType).Len() == 0 {
	return nil, nil
	}

	// Find all named types, even local types (which can have methods
	// due to promotion).
	var (
	allNamed []*types.Named
	pkgs = make(map[*types.Package]Package)
	)
	knownPkgs, err := s.KnownPackages(ctx)
	if err != nil {
	return nil, err
	}
	for _, pkg := range knownPkgs {
	pkgs[pkg.GetTypes()] = pkg
	info := pkg.GetTypesInfo()
	for _, obj := range info.Defs {
	obj, ok := obj.(*types.TypeName)
	// We ignore aliases 'type M = N' to avoid duplicate reporting
	// of the Named type N.
	if !ok \|\| obj.IsAlias() {
	continue
	}
	if named, ok := obj.Type().(*types.Named); ok {
	allNamed = append(allNamed, named)
	}
	}
	}

	// Find all the named types that match our query.
	for _, named := range allNamed {
	var (
	candObj types.Object = named.Obj()
	candType = ensurePointer(named)
	)

	if !concreteImplementsIntf(candType, queryType) {
	continue
	}

	ms := types.NewMethodSet(candType)
	if ms.Len() == 0 {
	// Skip empty interfaces.
	continue
	}

	// If client queried a method, look up corresponding candType method.
	if queryMethod != nil {
	sel := ms.Lookup(queryMethod.Pkg(), queryMethod.Name())
	if sel == nil {
	continue
	}
	candObj = sel.Obj()
	}

	pos := fset.Position(candObj.Pos())
	if candObj == queryMethod \|\| seen[pos] {
	continue
	}

	seen[pos] = true

	impls = append(impls, qualifiedObject{
	obj: candObj,
	pkg: pkgs[candObj.Pkg()],
	})
	}
	}

	return impls, nil
	}

	// concreteImplementsIntf returns true if a is an interface type implemented by
	// concrete type b, or vice versa.
	func concreteImplementsIntf(a, b types.Type) bool {
	aIsIntf, bIsIntf := IsInterface(a), IsInterface(b)

	// Make sure exactly one is an interface type.
	if aIsIntf == bIsIntf {
	return false
	}

	// Rearrange if needed so "a" is the concrete type.
	if aIsIntf {
	a, b = b, a
	}

	return types.AssignableTo(a, b)
	}

	// ensurePointer wraps T in a *types.Pointer if T is a named, non-interface
	// type. This is useful to make sure you consider a named type's full method
	// set.
	func ensurePointer(T types.Type) types.Type {
	if _, ok := T.(*types.Named); ok && !IsInterface(T) {
	return types.NewPointer(T)
	}

	return T
	}

	type qualifiedObject struct {
	obj types.Object

	// pkg is the Package that contains obj's definition.
	pkg Package

	// node is the ast.Ident or ast.ImportSpec we followed to find obj, if any.
	node ast.Node

	// sourcePkg is the Package that contains node, if any.
	sourcePkg Package
	}

	var (
	errBuiltin = errors.New("builtin object")
	errNoObjectFound = errors.New("no object found")
	)

	// qualifiedObjsAtProtocolPos returns info for all the type.Objects
	// referenced at the given position. An object will be returned for
	// every package that the file belongs to, in every typechecking mode
	// applicable.
	func qualifiedObjsAtProtocolPos(ctx context.Context, s Snapshot, uri span.URI, pp protocol.Position) ([]qualifiedObject, error) {
	pkgs, err := s.PackagesForFile(ctx, uri, TypecheckAll)
	if err != nil {
	return nil, err
	}
	if len(pkgs) == 0 {
	return nil, errNoObjectFound
	}
	pkg := pkgs[0]
	var offset int
	pgf, err := pkg.File(uri)
	if err != nil {
	return nil, err
	}
	spn, err := pgf.Mapper.PointSpan(pp)
	if err != nil {
	return nil, err
	}
	rng, err := spn.Range(pgf.Mapper.Converter)
	if err != nil {
	return nil, err
	}
	offset = pgf.Tok.Offset(rng.Start)
	return qualifiedObjsAtLocation(ctx, s, objSearchKey{uri, offset}, map[objSearchKey]bool{})
	}

	type objSearchKey struct {
	uri span.URI
	offset int
	}

	// qualifiedObjsAtLocation finds all objects referenced at offset in uri, across
	// all packages in the snapshot.
	func qualifiedObjsAtLocation(ctx context.Context, s Snapshot, key objSearchKey, seen map[objSearchKey]bool) ([]qualifiedObject, error) {
	if seen[key] {
	return nil, nil
	}
	seen[key] = true

	// We search for referenced objects starting with all packages containing the
	// current location, and then repeating the search for every distinct object
	// location discovered.
	//
	// In the common case, there should be at most one additional location to
	// consider: the definition of the object referenced by the location. But we
	// try to be comprehensive in case we ever support variations on build
	// constraints.

	pkgs, err := s.PackagesForFile(ctx, key.uri, TypecheckAll)
	if err != nil {
	return nil, err
	}

	// report objects in the order we encounter them. This ensures that the first
	// result is at the cursor...
	var qualifiedObjs []qualifiedObject
	// ...but avoid duplicates.
	seenObjs := map[types.Object]bool{}

	for _, searchpkg := range pkgs {
	pgf, err := searchpkg.File(key.uri)
	if err != nil {
	return nil, err
	}
	pos := pgf.Tok.Pos(key.offset)
	path := pathEnclosingObjNode(pgf.File, pos)
	if path == nil {
	continue
	}
	var objs []types.Object
	switch leaf := path[0].(type) {
	case *ast.Ident:
	// If leaf represents an implicit type switch object or the type
	// switch "assign" variable, expand to all of the type switch's
	// implicit objects.
	if implicits, _ := typeSwitchImplicits(searchpkg, path); len(implicits) > 0 {
	objs = append(objs, implicits...)
	} else {
	obj := searchpkg.GetTypesInfo().ObjectOf(leaf)
	if obj == nil {
	return nil, xerrors.Errorf("%w for %q", errNoObjectFound, leaf.Name)
	}
	objs = append(objs, obj)
	}
	case *ast.ImportSpec:
	// Look up the implicit *types.PkgName.
	obj := searchpkg.GetTypesInfo().Implicits[leaf]
	if obj == nil {
	return nil, xerrors.Errorf("%w for import %q", errNoObjectFound, ImportPath(leaf))
	}
	objs = append(objs, obj)
	}
	// Get all of the transitive dependencies of the search package.
	pkgs := make(map[*types.Package]Package)
	var addPkg func(pkg Package)
	addPkg = func(pkg Package) {
	pkgs[pkg.GetTypes()] = pkg
	for _, imp := range pkg.Imports() {
	if _, ok := pkgs[imp.GetTypes()]; !ok {
	addPkg(imp)
	}
	}
	}
	addPkg(searchpkg)
	for _, obj := range objs {
	if obj.Parent() == types.Universe {
	return nil, xerrors.Errorf("%q: %w", obj.Name(), errBuiltin)
	}
	pkg, ok := pkgs[obj.Pkg()]
	if !ok {
	event.Error(ctx, fmt.Sprintf("no package for obj %s: %v", obj, obj.Pkg()), err)
	continue
	}
	qualifiedObjs = append(qualifiedObjs, qualifiedObject{
	obj: obj,
	pkg: pkg,
	sourcePkg: searchpkg,
	node: path[0],
	})
	seenObjs[obj] = true

	// If the qualified object is in another file (or more likely, another
	// package), it's possible that there is another copy of it in a package
	// that we haven't searched, e.g. a test variant. See golang/go#47564.
	//
	// In order to be sure we've considered all packages, call
	// qualifiedObjsAtLocation recursively for all locations we encounter. We
	// could probably be more precise here, only continuing the search if obj
	// is in another package, but this should be good enough to find all
	// uses.

	pos := obj.Pos()
	var uri span.URI
	offset := -1
	for _, pgf := range pkg.CompiledGoFiles() {
	if pgf.Tok.Base() <= int(pos) && int(pos) <= pgf.Tok.Base()+pgf.Tok.Size() {
	offset = pgf.Tok.Offset(pos)
	uri = pgf.URI
	}
	}
	if offset >= 0 {
	otherObjs, err := qualifiedObjsAtLocation(ctx, s, objSearchKey{uri, offset}, seen)
	if err != nil {
	return nil, err
	}
	for _, other := range otherObjs {
	if !seenObjs[other.obj] {
	qualifiedObjs = append(qualifiedObjs, other)
	seenObjs[other.obj] = true
	}
	}
	} else {
	return nil, fmt.Errorf("missing file for position of %q in %q", obj.Name(), obj.Pkg().Name())
	}
	}
	}
	// Return an error if no objects were found since callers will assume that
	// the slice has at least 1 element.
	if len(qualifiedObjs) == 0 {
	return nil, errNoObjectFound
	}
	return qualifiedObjs, nil
	}

	// pathEnclosingObjNode returns the AST path to the object-defining
	// node associated with pos. "Object-defining" means either an
	// *ast.Ident mapped directly to a types.Object or an ast.Node mapped
	// implicitly to a types.Object.
	func pathEnclosingObjNode(f *ast.File, pos token.Pos) []ast.Node {
	var (
	path []ast.Node
	found bool
	)

	ast.Inspect(f, func(n ast.Node) bool {
	if found {
	return false
	}

	if n == nil {
	path = path[:len(path)-1]
	return false
	}

	path = append(path, n)

	switch n := n.(type) {
	case *ast.Ident:
	// Include the position directly after identifier. This handles
	// the common case where the cursor is right after the
	// identifier the user is currently typing. Previously we
	// handled this by calling astutil.PathEnclosingInterval twice,
	// once for "pos" and once for "pos-1".
	found = n.Pos() <= pos && pos <= n.End()
	case *ast.ImportSpec:
	if n.Path.Pos() <= pos && pos < n.Path.End() {
	found = true
	// If import spec has a name, add name to path even though
	// position isn't in the name.
	if n.Name != nil {
	path = append(path, n.Name)
	}
	}
	case *ast.StarExpr:
	// Follow star expressions to the inner identifier.
	if pos == n.Star {
	pos = n.X.Pos()
	}
	}

	return !found
	})

	if len(path) == 0 {
	return nil
	}

	// Reverse path so leaf is first element.
	for i := 0; i < len(path)/2; i++ {
	path[i], path[len(path)-1-i] = path[len(path)-1-i], path[i]
	}

	return path
	}