internal/lsp/source/util.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"
 	"go/ast"
 	"go/printer"
 	"go/token"
 	"go/types"
 	"path/filepath"
 	"regexp"
 	"sort"
 	"strconv"
 	"strings"

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

 // MappedRange provides mapped protocol.Range for a span.Range, accounting for
 // UTF-16 code points.
 type MappedRange struct {
 	spanRange span.Range
 	m         *protocol.ColumnMapper

 	// protocolRange is the result of converting the spanRange using the mapper.
 	// It is computed on-demand.
 	protocolRange *protocol.Range
 }

 // NewMappedRange returns a MappedRange for the given start and end token.Pos.
 func NewMappedRange(fset *token.FileSet, m *protocol.ColumnMapper, start, end token.Pos) MappedRange {
 	return MappedRange{
 		spanRange: span.Range{
 			FileSet:   fset,
 			Start:     start,
 			End:       end,
 			Converter: m.Converter,
 		},
 		m: m,
 	}
 }

 func (s MappedRange) Range() (protocol.Range, error) {
 	if s.protocolRange == nil {
 		spn, err := s.spanRange.Span()
 		if err != nil {
 			return protocol.Range{}, err
 		}
 		prng, err := s.m.Range(spn)
 		if err != nil {
 			return protocol.Range{}, err
 		}
 		s.protocolRange = &prng
 	}
 	return *s.protocolRange, nil
 }

 func (s MappedRange) Span() (span.Span, error) {
 	return s.spanRange.Span()
 }

 func (s MappedRange) SpanRange() span.Range {
 	return s.spanRange
 }

 func (s MappedRange) URI() span.URI {
 	return s.m.URI
 }

 // GetParsedFile is a convenience function that extracts the Package and
 // ParsedGoFile for a file in a Snapshot. pkgPolicy is one of NarrowestPackage/
 // WidestPackage.
 func GetParsedFile(ctx context.Context, snapshot Snapshot, fh FileHandle, pkgPolicy PackageFilter) (Package, *ParsedGoFile, error) {
 	pkg, err := snapshot.PackageForFile(ctx, fh.URI(), TypecheckWorkspace, pkgPolicy)
 	if err != nil {
 		return nil, nil, err
 	}
 	pgh, err := pkg.File(fh.URI())
 	return pkg, pgh, err
 }

 func IsGenerated(ctx context.Context, snapshot Snapshot, uri span.URI) bool {
 	fh, err := snapshot.GetFile(ctx, uri)
 	if err != nil {
 		return false
 	}
 	pgf, err := snapshot.ParseGo(ctx, fh, ParseHeader)
 	if err != nil {
 		return false
 	}
 	tok := snapshot.FileSet().File(pgf.File.Pos())
 	if tok == nil {
 		return false
 	}
 	for _, commentGroup := range pgf.File.Comments {
 		for _, comment := range commentGroup.List {
 			if matched := generatedRx.MatchString(comment.Text); matched {
 				// Check if comment is at the beginning of the line in source.
 				if pos := tok.Position(comment.Slash); pos.Column == 1 {
 					return true
 				}
 			}
 		}
 	}
 	return false
 }

 func nodeToProtocolRange(snapshot Snapshot, pkg Package, n ast.Node) (protocol.Range, error) {
 	mrng, err := posToMappedRange(snapshot, pkg, n.Pos(), n.End())
 	if err != nil {
 		return protocol.Range{}, err
 	}
 	return mrng.Range()
 }

 func objToMappedRange(snapshot Snapshot, pkg Package, obj types.Object) (MappedRange, error) {
 	if pkgName, ok := obj.(*types.PkgName); ok {
 		// An imported Go package has a package-local, unqualified name.
 		// When the name matches the imported package name, there is no
 		// identifier in the import spec with the local package name.
 		//
 		// For example:
 		// 		import "go/ast" 	// name "ast" matches package name
 		// 		import a "go/ast"  	// name "a" does not match package name
 		//
 		// When the identifier does not appear in the source, have the range
 		// of the object be the import path, including quotes.
 		if pkgName.Imported().Name() == pkgName.Name() {
 			return posToMappedRange(snapshot, pkg, obj.Pos(), obj.Pos()+token.Pos(len(pkgName.Imported().Path())+2))
 		}
 	}
 	return nameToMappedRange(snapshot, pkg, obj.Pos(), obj.Name())
 }

 func nameToMappedRange(snapshot Snapshot, pkg Package, pos token.Pos, name string) (MappedRange, error) {
 	return posToMappedRange(snapshot, pkg, pos, pos+token.Pos(len(name)))
 }

 func posToMappedRange(snapshot Snapshot, pkg Package, pos, end token.Pos) (MappedRange, error) {
 	logicalFilename := snapshot.FileSet().File(pos).Position(pos).Filename
 	pgf, _, err := findFileInDeps(pkg, span.URIFromPath(logicalFilename))
 	if err != nil {
 		return MappedRange{}, err
 	}
 	if !pos.IsValid() {
 		return MappedRange{}, errors.Errorf("invalid position for %v", pos)
 	}
 	if !end.IsValid() {
 		return MappedRange{}, errors.Errorf("invalid position for %v", end)
 	}
 	return NewMappedRange(snapshot.FileSet(), pgf.Mapper, pos, end), nil
 }

 // Matches cgo generated comment as well as the proposed standard:
 //	https://golang.org/s/generatedcode
 var generatedRx = regexp.MustCompile(`// .*DO NOT EDIT\.?`)

 func DetectLanguage(langID, filename string) FileKind {
 	switch langID {
 	case "go":
 		return Go
 	case "go.mod":
 		return Mod
 	case "go.sum":
 		return Sum
 	case "tmpl":
 		return Tmpl
 	}
 	// Fallback to detecting the language based on the file extension.
 	switch ext := filepath.Ext(filename); ext {
 	case ".mod":
 		return Mod
 	case ".sum":
 		return Sum
 	default:
 		if strings.HasSuffix(ext, "tmpl") {
 			// .tmpl, .gotmpl, etc
 			return Tmpl
 		}
 		// It's a Go file, or we shouldn't be seeing it
 		return Go
 	}
 }

 func (k FileKind) String() string {
 	switch k {
 	case Mod:
 		return "go.mod"
 	case Sum:
 		return "go.sum"
 	case Tmpl:
 		return "tmpl"
 	default:
 		return "go"
 	}
 }

 // nodeAtPos returns the index and the node whose position is contained inside
 // the node list.
 func nodeAtPos(nodes []ast.Node, pos token.Pos) (ast.Node, int) {
 	if nodes == nil {
 		return nil, -1
 	}
 	for i, node := range nodes {
 		if node.Pos() <= pos && pos <= node.End() {
 			return node, i
 		}
 	}
 	return nil, -1
 }

 // IsInterface returns if a types.Type is an interface
 func IsInterface(T types.Type) bool {
 	return T != nil && types.IsInterface(T)
 }

 // FormatNode returns the "pretty-print" output for an ast node.
 func FormatNode(fset *token.FileSet, n ast.Node) string {
 	var buf strings.Builder
 	if err := printer.Fprint(&buf, fset, n); err != nil {
 		return ""
 	}
 	return buf.String()
 }

 // Deref returns a pointer's element type, traversing as many levels as needed.
 // Otherwise it returns typ.
 //
 // It can return a pointer type for cyclic types (see golang/go#45510).
 func Deref(typ types.Type) types.Type {
 	var seen map[types.Type]struct{}
 	for {
 		p, ok := typ.Underlying().(*types.Pointer)
 		if !ok {
 			return typ
 		}
 		if _, ok := seen[p.Elem()]; ok {
 			return typ
 		}

 		typ = p.Elem()

 		if seen == nil {
 			seen = make(map[types.Type]struct{})
 		}
 		seen[typ] = struct{}{}
 	}
 }

 func SortDiagnostics(d []*Diagnostic) {
 	sort.Slice(d, func(i int, j int) bool {
 		return CompareDiagnostic(d[i], d[j]) < 0
 	})
 }

 func CompareDiagnostic(a, b *Diagnostic) int {
 	if r := protocol.CompareRange(a.Range, b.Range); r != 0 {
 		return r
 	}
 	if a.Source < b.Source {
 		return -1
 	}
 	if a.Message < b.Message {
 		return -1
 	}
 	if a.Message == b.Message {
 		return 0
 	}
 	return 1
 }

 // FindPackageFromPos finds the first package containing pos in its
 // type-checked AST.
 func FindPackageFromPos(ctx context.Context, snapshot Snapshot, pos token.Pos) (Package, error) {
 	tok := snapshot.FileSet().File(pos)
 	if tok == nil {
 		return nil, errors.Errorf("no file for pos %v", pos)
 	}
 	uri := span.URIFromPath(tok.Name())
 	// Search all packages: some callers may be working with packages not
 	// type-checked in workspace mode.
 	pkgs, err := snapshot.PackagesForFile(ctx, uri, TypecheckAll)
 	if err != nil {
 		return nil, err
 	}
 	// Only return the package if it actually type-checked the given position.
 	for _, pkg := range pkgs {
 		parsed, err := pkg.File(uri)
 		if err != nil {
 			return nil, err
 		}
 		if parsed == nil {
 			continue
 		}
 		if parsed.Tok.Base() != tok.Base() {
 			continue
 		}
 		return pkg, nil
 	}
 	return nil, errors.Errorf("no package for given file position")
 }

 // findFileInDeps finds uri in pkg or its dependencies.
 func findFileInDeps(pkg Package, uri span.URI) (*ParsedGoFile, Package, error) {
 	queue := []Package{pkg}
 	seen := make(map[string]bool)

 	for len(queue) > 0 {
 		pkg := queue[0]
 		queue = queue[1:]
 		seen[pkg.ID()] = true

 		if pgf, err := pkg.File(uri); err == nil {
 			return pgf, pkg, nil
 		}
 		for _, dep := range pkg.Imports() {
 			if !seen[dep.ID()] {
 				queue = append(queue, dep)
 			}
 		}
 	}
 	return nil, nil, errors.Errorf("no file for %s in package %s", uri, pkg.ID())
 }

 // ImportPath returns the unquoted import path of s,
 // or "" if the path is not properly quoted.
 func ImportPath(s *ast.ImportSpec) string {
 	t, err := strconv.Unquote(s.Path.Value)
 	if err != nil {
 		return ""
 	}
 	return t
 }

 // NodeContains returns true if a node encloses a given position pos.
 func NodeContains(n ast.Node, pos token.Pos) bool {
 	return n != nil && n.Pos() <= pos && pos <= n.End()
 }

 // CollectScopes returns all scopes in an ast path, ordered as innermost scope
 // first.
 func CollectScopes(info *types.Info, path []ast.Node, pos token.Pos) []*types.Scope {
 	// scopes[i], where i<len(path), is the possibly nil Scope of path[i].
 	var scopes []*types.Scope
 	for _, n := range path {
 		// Include *FuncType scope if pos is inside the function body.
 		switch node := n.(type) {
 		case *ast.FuncDecl:
 			if node.Body != nil && NodeContains(node.Body, pos) {
 				n = node.Type
 			}
 		case *ast.FuncLit:
 			if node.Body != nil && NodeContains(node.Body, pos) {
 				n = node.Type
 			}
 		}
 		scopes = append(scopes, info.Scopes[n])
 	}
 	return scopes
 }

 // Qualifier returns a function that appropriately formats a types.PkgName
 // appearing in a *ast.File.
 func Qualifier(f *ast.File, pkg *types.Package, info *types.Info) types.Qualifier {
 	// Construct mapping of import paths to their defined or implicit names.
 	imports := make(map[*types.Package]string)
 	for _, imp := range f.Imports {
 		var obj types.Object
 		if imp.Name != nil {
 			obj = info.Defs[imp.Name]
 		} else {
 			obj = info.Implicits[imp]
 		}
 		if pkgname, ok := obj.(*types.PkgName); ok {
 			imports[pkgname.Imported()] = pkgname.Name()
 		}
 	}
 	// Define qualifier to replace full package paths with names of the imports.
 	return func(p *types.Package) string {
 		if p == pkg {
 			return ""
 		}
 		if name, ok := imports[p]; ok {
 			if name == "." {
 				return ""
 			}
 			return name
 		}
 		return p.Name()
 	}
 }

 // isDirective reports whether c is a comment directive.
 //
 // Copied and adapted from go/src/go/ast/ast.go.
 func isDirective(c string) bool {
 	if len(c) < 3 {
 		return false
 	}
 	if c[1] != '/' {
 		return false
 	}
 	//-style comment (no newline at the end)
 	c = c[2:]
 	if len(c) == 0 {
 		// empty line
 		return false
 	}
 	// "//line " is a line directive.
 	// (The // has been removed.)
 	if strings.HasPrefix(c, "line ") {
 		return true
 	}

 	// "//[a-z0-9]+:[a-z0-9]"
 	// (The // has been removed.)
 	colon := strings.Index(c, ":")
 	if colon <= 0 || colon+1 >= len(c) {
 		return false
 	}
 	for i := 0; i <= colon+1; i++ {
 		if i == colon {
 			continue
 		}
 		b := c[i]
 		if !('a' <= b && b <= 'z' || '0' <= b && b <= '9') {
 			return false
 		}
 	}
 	return true
 }

 // honorSymlinks toggles whether or not we consider symlinks when comparing
 // file or directory URIs.
 const honorSymlinks = false

 func CompareURI(left, right span.URI) int {
 	if honorSymlinks {
 		return span.CompareURI(left, right)
 	}
 	if left == right {
 		return 0
 	}
 	if left < right {
 		return -1
 	}
 	return 1
 }

 // InDir checks whether path is in the file tree rooted at dir.
 // InDir makes some effort to succeed even in the presence of symbolic links.
 //
 // Copied and slightly adjusted from go/src/cmd/go/internal/search/search.go.
 func InDir(dir, path string) bool {
 	if inDirLex(dir, path) {
 		return true
 	}
 	if !honorSymlinks {
 		return false
 	}
 	xpath, err := filepath.EvalSymlinks(path)
 	if err != nil || xpath == path {
 		xpath = ""
 	} else {
 		if inDirLex(dir, xpath) {
 			return true
 		}
 	}

 	xdir, err := filepath.EvalSymlinks(dir)
 	if err == nil && xdir != dir {
 		if inDirLex(xdir, path) {
 			return true
 		}
 		if xpath != "" {
 			if inDirLex(xdir, xpath) {
 				return true
 			}
 		}
 	}
 	return false
 }

 // inDirLex is like inDir but only checks the lexical form of the file names.
 // It does not consider symbolic links.
 //
 // Copied from go/src/cmd/go/internal/search/search.go.
 func inDirLex(dir, path string) bool {
 	pv := strings.ToUpper(filepath.VolumeName(path))
 	dv := strings.ToUpper(filepath.VolumeName(dir))
 	path = path[len(pv):]
 	dir = dir[len(dv):]
 	switch {
 	default:
 		return false
 	case pv != dv:
 		return false
 	case len(path) == len(dir):
 		if path == dir {
 			return true
 		}
 		return false
 	case dir == "":
 		return path != ""
 	case len(path) > len(dir):
 		if dir[len(dir)-1] == filepath.Separator {
 			if path[:len(dir)] == dir {
 				return path[len(dir):] != ""
 			}
 			return false
 		}
 		if path[len(dir)] == filepath.Separator && path[:len(dir)] == dir {
 			if len(path) == len(dir)+1 {
 				return true
 			}
 			return path[len(dir)+1:] != ""
 		}
 		return false
 	}
 }

 // IsValidImport returns whether importPkgPath is importable
 // by pkgPath
 func IsValidImport(pkgPath, importPkgPath string) bool {
 	i := strings.LastIndex(string(importPkgPath), "/internal/")
 	if i == -1 {
 		return true
 	}
 	if IsCommandLineArguments(string(pkgPath)) {
 		return true
 	}
 	return strings.HasPrefix(string(pkgPath), string(importPkgPath[:i]))
 }

 // IsCommandLineArguments reports whether a given value denotes
 // "command-line-arguments" package, which is a package with an unknown ID
 // created by the go command. It can have a test variant, which is why callers
 // should not check that a value equals "command-line-arguments" directly.
 func IsCommandLineArguments(s string) bool {
 	return strings.Contains(s, "command-line-arguments")
 }

 // InRange reports whether the given position is in the given token.File.
 func InRange(tok *token.File, pos token.Pos) bool {
 	size := tok.Pos(tok.Size())
 	return int(pos) >= tok.Base() && pos <= size
 }
	// 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"
	"go/ast"
	"go/printer"
	"go/token"
	"go/types"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"

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

	// MappedRange provides mapped protocol.Range for a span.Range, accounting for
	// UTF-16 code points.
	type MappedRange struct {
	spanRange span.Range
	m *protocol.ColumnMapper

	// protocolRange is the result of converting the spanRange using the mapper.
	// It is computed on-demand.
	protocolRange *protocol.Range
	}

	// NewMappedRange returns a MappedRange for the given start and end token.Pos.
	func NewMappedRange(fset token.FileSet, m protocol.ColumnMapper, start, end token.Pos) MappedRange {
	return MappedRange{
	spanRange: span.Range{
	FileSet: fset,
	Start: start,
	End: end,
	Converter: m.Converter,
	},
	m: m,
	}
	}

	func (s MappedRange) Range() (protocol.Range, error) {
	if s.protocolRange == nil {
	spn, err := s.spanRange.Span()
	if err != nil {
	return protocol.Range{}, err
	}
	prng, err := s.m.Range(spn)
	if err != nil {
	return protocol.Range{}, err
	}
	s.protocolRange = &prng
	}
	return *s.protocolRange, nil
	}

	func (s MappedRange) Span() (span.Span, error) {
	return s.spanRange.Span()
	}

	func (s MappedRange) SpanRange() span.Range {
	return s.spanRange
	}

	func (s MappedRange) URI() span.URI {
	return s.m.URI
	}

	// GetParsedFile is a convenience function that extracts the Package and
	// ParsedGoFile for a file in a Snapshot. pkgPolicy is one of NarrowestPackage/
	// WidestPackage.
	func GetParsedFile(ctx context.Context, snapshot Snapshot, fh FileHandle, pkgPolicy PackageFilter) (Package, *ParsedGoFile, error) {
	pkg, err := snapshot.PackageForFile(ctx, fh.URI(), TypecheckWorkspace, pkgPolicy)
	if err != nil {
	return nil, nil, err
	}
	pgh, err := pkg.File(fh.URI())
	return pkg, pgh, err
	}

	func IsGenerated(ctx context.Context, snapshot Snapshot, uri span.URI) bool {
	fh, err := snapshot.GetFile(ctx, uri)
	if err != nil {
	return false
	}
	pgf, err := snapshot.ParseGo(ctx, fh, ParseHeader)
	if err != nil {
	return false
	}
	tok := snapshot.FileSet().File(pgf.File.Pos())
	if tok == nil {
	return false
	}
	for _, commentGroup := range pgf.File.Comments {
	for _, comment := range commentGroup.List {
	if matched := generatedRx.MatchString(comment.Text); matched {
	// Check if comment is at the beginning of the line in source.
	if pos := tok.Position(comment.Slash); pos.Column == 1 {
	return true
	}
	}
	}
	}
	return false
	}

	func nodeToProtocolRange(snapshot Snapshot, pkg Package, n ast.Node) (protocol.Range, error) {
	mrng, err := posToMappedRange(snapshot, pkg, n.Pos(), n.End())
	if err != nil {
	return protocol.Range{}, err
	}
	return mrng.Range()
	}

	func objToMappedRange(snapshot Snapshot, pkg Package, obj types.Object) (MappedRange, error) {
	if pkgName, ok := obj.(*types.PkgName); ok {
	// An imported Go package has a package-local, unqualified name.
	// When the name matches the imported package name, there is no
	// identifier in the import spec with the local package name.
	//
	// For example:
	// import "go/ast" // name "ast" matches package name
	// import a "go/ast" // name "a" does not match package name
	//
	// When the identifier does not appear in the source, have the range
	// of the object be the import path, including quotes.
	if pkgName.Imported().Name() == pkgName.Name() {
	return posToMappedRange(snapshot, pkg, obj.Pos(), obj.Pos()+token.Pos(len(pkgName.Imported().Path())+2))
	}
	}
	return nameToMappedRange(snapshot, pkg, obj.Pos(), obj.Name())
	}

	func nameToMappedRange(snapshot Snapshot, pkg Package, pos token.Pos, name string) (MappedRange, error) {
	return posToMappedRange(snapshot, pkg, pos, pos+token.Pos(len(name)))
	}

	func posToMappedRange(snapshot Snapshot, pkg Package, pos, end token.Pos) (MappedRange, error) {
	logicalFilename := snapshot.FileSet().File(pos).Position(pos).Filename
	pgf, _, err := findFileInDeps(pkg, span.URIFromPath(logicalFilename))
	if err != nil {
	return MappedRange{}, err
	}
	if !pos.IsValid() {
	return MappedRange{}, errors.Errorf("invalid position for %v", pos)
	}
	if !end.IsValid() {
	return MappedRange{}, errors.Errorf("invalid position for %v", end)
	}
	return NewMappedRange(snapshot.FileSet(), pgf.Mapper, pos, end), nil
	}

	// Matches cgo generated comment as well as the proposed standard:
	// https://golang.org/s/generatedcode
	var generatedRx = regexp.MustCompile(`// .*DO NOT EDIT\.?`)

	func DetectLanguage(langID, filename string) FileKind {
	switch langID {
	case "go":
	return Go
	case "go.mod":
	return Mod
	case "go.sum":
	return Sum
	case "tmpl":
	return Tmpl
	}
	// Fallback to detecting the language based on the file extension.
	switch ext := filepath.Ext(filename); ext {
	case ".mod":
	return Mod
	case ".sum":
	return Sum
	default:
	if strings.HasSuffix(ext, "tmpl") {
	// .tmpl, .gotmpl, etc
	return Tmpl
	}
	// It's a Go file, or we shouldn't be seeing it
	return Go
	}
	}

	func (k FileKind) String() string {
	switch k {
	case Mod:
	return "go.mod"
	case Sum:
	return "go.sum"
	case Tmpl:
	return "tmpl"
	default:
	return "go"
	}
	}

	// nodeAtPos returns the index and the node whose position is contained inside
	// the node list.
	func nodeAtPos(nodes []ast.Node, pos token.Pos) (ast.Node, int) {
	if nodes == nil {
	return nil, -1
	}
	for i, node := range nodes {
	if node.Pos() <= pos && pos <= node.End() {
	return node, i
	}
	}
	return nil, -1
	}

	// IsInterface returns if a types.Type is an interface
	func IsInterface(T types.Type) bool {
	return T != nil && types.IsInterface(T)
	}

	// FormatNode returns the "pretty-print" output for an ast node.
	func FormatNode(fset *token.FileSet, n ast.Node) string {
	var buf strings.Builder
	if err := printer.Fprint(&buf, fset, n); err != nil {
	return ""
	}
	return buf.String()
	}

	// Deref returns a pointer's element type, traversing as many levels as needed.
	// Otherwise it returns typ.
	//
	// It can return a pointer type for cyclic types (see golang/go#45510).
	func Deref(typ types.Type) types.Type {
	var seen map[types.Type]struct{}
	for {
	p, ok := typ.Underlying().(*types.Pointer)
	if !ok {
	return typ
	}
	if _, ok := seen[p.Elem()]; ok {
	return typ
	}

	typ = p.Elem()

	if seen == nil {
	seen = make(map[types.Type]struct{})
	}
	seen[typ] = struct{}{}
	}
	}

	func SortDiagnostics(d []*Diagnostic) {
	sort.Slice(d, func(i int, j int) bool {
	return CompareDiagnostic(d[i], d[j]) < 0
	})
	}

	func CompareDiagnostic(a, b *Diagnostic) int {
	if r := protocol.CompareRange(a.Range, b.Range); r != 0 {
	return r
	}
	if a.Source < b.Source {
	return -1
	}
	if a.Message < b.Message {
	return -1
	}
	if a.Message == b.Message {
	return 0
	}
	return 1
	}

	// FindPackageFromPos finds the first package containing pos in its
	// type-checked AST.
	func FindPackageFromPos(ctx context.Context, snapshot Snapshot, pos token.Pos) (Package, error) {
	tok := snapshot.FileSet().File(pos)
	if tok == nil {
	return nil, errors.Errorf("no file for pos %v", pos)
	}
	uri := span.URIFromPath(tok.Name())
	// Search all packages: some callers may be working with packages not
	// type-checked in workspace mode.
	pkgs, err := snapshot.PackagesForFile(ctx, uri, TypecheckAll)
	if err != nil {
	return nil, err
	}
	// Only return the package if it actually type-checked the given position.
	for _, pkg := range pkgs {
	parsed, err := pkg.File(uri)
	if err != nil {
	return nil, err
	}
	if parsed == nil {
	continue
	}
	if parsed.Tok.Base() != tok.Base() {
	continue
	}
	return pkg, nil
	}
	return nil, errors.Errorf("no package for given file position")
	}

	// findFileInDeps finds uri in pkg or its dependencies.
	func findFileInDeps(pkg Package, uri span.URI) (*ParsedGoFile, Package, error) {
	queue := []Package{pkg}
	seen := make(map[string]bool)

	for len(queue) > 0 {
	pkg := queue[0]
	queue = queue[1:]
	seen[pkg.ID()] = true

	if pgf, err := pkg.File(uri); err == nil {
	return pgf, pkg, nil
	}
	for _, dep := range pkg.Imports() {
	if !seen[dep.ID()] {
	queue = append(queue, dep)
	}
	}
	}
	return nil, nil, errors.Errorf("no file for %s in package %s", uri, pkg.ID())
	}

	// ImportPath returns the unquoted import path of s,
	// or "" if the path is not properly quoted.
	func ImportPath(s *ast.ImportSpec) string {
	t, err := strconv.Unquote(s.Path.Value)
	if err != nil {
	return ""
	}
	return t
	}

	// NodeContains returns true if a node encloses a given position pos.
	func NodeContains(n ast.Node, pos token.Pos) bool {
	return n != nil && n.Pos() <= pos && pos <= n.End()
	}

	// CollectScopes returns all scopes in an ast path, ordered as innermost scope
	// first.
	func CollectScopes(info types.Info, path []ast.Node, pos token.Pos) []types.Scope {
	// scopes[i], where i<len(path), is the possibly nil Scope of path[i].
	var scopes []*types.Scope
	for _, n := range path {
	// Include *FuncType scope if pos is inside the function body.
	switch node := n.(type) {
	case *ast.FuncDecl:
	if node.Body != nil && NodeContains(node.Body, pos) {
	n = node.Type
	}
	case *ast.FuncLit:
	if node.Body != nil && NodeContains(node.Body, pos) {
	n = node.Type
	}
	}
	scopes = append(scopes, info.Scopes[n])
	}
	return scopes
	}

	// Qualifier returns a function that appropriately formats a types.PkgName
	// appearing in a *ast.File.
	func Qualifier(f ast.File, pkg types.Package, info *types.Info) types.Qualifier {
	// Construct mapping of import paths to their defined or implicit names.
	imports := make(map[*types.Package]string)
	for _, imp := range f.Imports {
	var obj types.Object
	if imp.Name != nil {
	obj = info.Defs[imp.Name]
	} else {
	obj = info.Implicits[imp]
	}
	if pkgname, ok := obj.(*types.PkgName); ok {
	imports[pkgname.Imported()] = pkgname.Name()
	}
	}
	// Define qualifier to replace full package paths with names of the imports.
	return func(p *types.Package) string {
	if p == pkg {
	return ""
	}
	if name, ok := imports[p]; ok {
	if name == "." {
	return ""
	}
	return name
	}
	return p.Name()
	}
	}

	// isDirective reports whether c is a comment directive.
	//
	// Copied and adapted from go/src/go/ast/ast.go.
	func isDirective(c string) bool {
	if len(c) < 3 {
	return false
	}
	if c[1] != '/' {
	return false
	}
	//-style comment (no newline at the end)
	c = c[2:]
	if len(c) == 0 {
	// empty line
	return false
	}
	// "//line " is a line directive.
	// (The // has been removed.)
	if strings.HasPrefix(c, "line ") {
	return true
	}

	// "//[a-z0-9]+:[a-z0-9]"
	// (The // has been removed.)
	colon := strings.Index(c, ":")
	if colon <= 0 \|\| colon+1 >= len(c) {
	return false
	}
	for i := 0; i <= colon+1; i++ {
	if i == colon {
	continue
	}
	b := c[i]
	if !('a' <= b && b <= 'z' \|\| '0' <= b && b <= '9') {
	return false
	}
	}
	return true
	}

	// honorSymlinks toggles whether or not we consider symlinks when comparing
	// file or directory URIs.
	const honorSymlinks = false

	func CompareURI(left, right span.URI) int {
	if honorSymlinks {
	return span.CompareURI(left, right)
	}
	if left == right {
	return 0
	}
	if left < right {
	return -1
	}
	return 1
	}

	// InDir checks whether path is in the file tree rooted at dir.
	// InDir makes some effort to succeed even in the presence of symbolic links.
	//
	// Copied and slightly adjusted from go/src/cmd/go/internal/search/search.go.
	func InDir(dir, path string) bool {
	if inDirLex(dir, path) {
	return true
	}
	if !honorSymlinks {
	return false
	}
	xpath, err := filepath.EvalSymlinks(path)
	if err != nil \|\| xpath == path {
	xpath = ""
	} else {
	if inDirLex(dir, xpath) {
	return true
	}
	}

	xdir, err := filepath.EvalSymlinks(dir)
	if err == nil && xdir != dir {
	if inDirLex(xdir, path) {
	return true
	}
	if xpath != "" {
	if inDirLex(xdir, xpath) {
	return true
	}
	}
	}
	return false
	}

	// inDirLex is like inDir but only checks the lexical form of the file names.
	// It does not consider symbolic links.
	//
	// Copied from go/src/cmd/go/internal/search/search.go.
	func inDirLex(dir, path string) bool {
	pv := strings.ToUpper(filepath.VolumeName(path))
	dv := strings.ToUpper(filepath.VolumeName(dir))
	path = path[len(pv):]
	dir = dir[len(dv):]
	switch {
	default:
	return false
	case pv != dv:
	return false
	case len(path) == len(dir):
	if path == dir {
	return true
	}
	return false
	case dir == "":
	return path != ""
	case len(path) > len(dir):
	if dir[len(dir)-1] == filepath.Separator {
	if path[:len(dir)] == dir {
	return path[len(dir):] != ""
	}
	return false
	}
	if path[len(dir)] == filepath.Separator && path[:len(dir)] == dir {
	if len(path) == len(dir)+1 {
	return true
	}
	return path[len(dir)+1:] != ""
	}
	return false
	}
	}

	// IsValidImport returns whether importPkgPath is importable
	// by pkgPath
	func IsValidImport(pkgPath, importPkgPath string) bool {
	i := strings.LastIndex(string(importPkgPath), "/internal/")
	if i == -1 {
	return true
	}
	if IsCommandLineArguments(string(pkgPath)) {
	return true
	}
	return strings.HasPrefix(string(pkgPath), string(importPkgPath[:i]))
	}

	// IsCommandLineArguments reports whether a given value denotes
	// "command-line-arguments" package, which is a package with an unknown ID
	// created by the go command. It can have a test variant, which is why callers
	// should not check that a value equals "command-line-arguments" directly.
	func IsCommandLineArguments(s string) bool {
	return strings.Contains(s, "command-line-arguments")
	}

	// InRange reports whether the given position is in the given token.File.
	func InRange(tok *token.File, pos token.Pos) bool {
	size := tok.Pos(tok.Size())
	return int(pos) >= tok.Base() && pos <= size
	}