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"
 	"fmt"
 	"go/ast"
 	"go/token"
 	"go/types"
 	"path/filepath"
 	"regexp"
 	"strings"

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

 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
 }

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

 // NarrowestCheckPackageHandle picks the "narrowest" package for a given file.
 //
 // By "narrowest" package, we mean the package with the fewest number of files
 // that includes the given file. This solves the problem of test variants,
 // as the test will have more files than the non-test package.
 func NarrowestCheckPackageHandle(handles []CheckPackageHandle) (CheckPackageHandle, error) {
 	if len(handles) < 1 {
 		return nil, errors.Errorf("no CheckPackageHandles")
 	}
 	result := handles[0]
 	for _, handle := range handles[1:] {
 		if result == nil || len(handle.Files()) < len(result.Files()) {
 			result = handle
 		}
 	}
 	if result == nil {
 		return nil, errors.Errorf("nil CheckPackageHandles have been returned")
 	}
 	return result, nil
 }

 // WidestCheckPackageHandle returns the CheckPackageHandle containing the most files.
 //
 // This is useful for something like diagnostics, where we'd prefer to offer diagnostics
 // for as many files as possible.
 func WidestCheckPackageHandle(handles []CheckPackageHandle) (CheckPackageHandle, error) {
 	if len(handles) < 1 {
 		return nil, errors.Errorf("no CheckPackageHandles")
 	}
 	result := handles[0]
 	for _, handle := range handles[1:] {
 		if result == nil || len(handle.Files()) > len(result.Files()) {
 			result = handle
 		}
 	}
 	if result == nil {
 		return nil, errors.Errorf("nil CheckPackageHandles have been returned")
 	}
 	return result, nil
 }

 func IsGenerated(ctx context.Context, view View, uri span.URI) bool {
 	f, err := view.GetFile(ctx, uri)
 	if err != nil {
 		return false
 	}
 	ph := view.Session().Cache().ParseGoHandle(view.Snapshot().Handle(ctx, f), ParseHeader)
 	parsed, _, _, err := ph.Parse(ctx)
 	if err != nil {
 		return false
 	}
 	tok := view.Session().Cache().FileSet().File(parsed.Pos())
 	if tok == nil {
 		return false
 	}
 	for _, commentGroup := range parsed.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(ctx context.Context, view View, m *protocol.ColumnMapper, n ast.Node) (protocol.Range, error) {
 	mrng, err := nodeToMappedRange(ctx, view, m, n)
 	if err != nil {
 		return protocol.Range{}, err
 	}
 	return mrng.Range()
 }

 func objToMappedRange(ctx context.Context, v View, 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 point at the beginning of the declaration.
 		if pkgName.Imported().Name() == pkgName.Name() {
 			return nameToMappedRange(ctx, v, pkg, obj.Pos(), "")
 		}
 	}
 	return nameToMappedRange(ctx, v, pkg, obj.Pos(), obj.Name())
 }

 func nameToMappedRange(ctx context.Context, v View, pkg Package, pos token.Pos, name string) (mappedRange, error) {
 	return posToMappedRange(ctx, v, pkg, pos, pos+token.Pos(len(name)))
 }

 func nodeToMappedRange(ctx context.Context, view View, m *protocol.ColumnMapper, n ast.Node) (mappedRange, error) {
 	return posToRange(ctx, view, m, n.Pos(), n.End())
 }

 func posToMappedRange(ctx context.Context, v View, pkg Package, pos, end token.Pos) (mappedRange, error) {
 	m, err := posToMapper(ctx, v, pkg, pos)
 	if err != nil {
 		return mappedRange{}, err
 	}
 	return posToRange(ctx, v, m, pos, end)
 }

 func posToRange(ctx context.Context, view View, m *protocol.ColumnMapper, pos, end token.Pos) (mappedRange, error) {
 	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 mappedRange{
 		m:         m,
 		spanRange: span.NewRange(view.Session().Cache().FileSet(), pos, end),
 	}, nil
 }

 func posToMapper(ctx context.Context, v View, pkg Package, pos token.Pos) (*protocol.ColumnMapper, error) {
 	posn := v.Session().Cache().FileSet().Position(pos)
 	ph, _, err := v.FindFileInPackage(ctx, span.FileURI(posn.Filename), pkg)
 	if err != nil {
 		return nil, err
 	}
 	_, m, _, err := ph.Cached()
 	return m, err
 }

 // 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
 	}
 	// Fallback to detecting the language based on the file extension.
 	switch filepath.Ext(filename) {
 	case ".mod":
 		return Mod
 	case ".sum":
 		return Sum
 	default: // fallback to Go
 		return Go
 	}
 }

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

 // indexExprAtPos returns the index of the expression containing pos.
 func indexExprAtPos(pos token.Pos, args []ast.Expr) int {
 	for i, expr := range args {
 		if expr.Pos() <= pos && pos <= expr.End() {
 			return i
 		}
 	}
 	return len(args)
 }

 func exprAtPos(pos token.Pos, args []ast.Expr) ast.Expr {
 	for _, expr := range args {
 		if expr.Pos() <= pos && pos <= expr.End() {
 			return expr
 		}
 	}
 	return nil
 }

 // fieldSelections returns the set of fields that can
 // be selected from a value of type T.
 func fieldSelections(T types.Type) (fields []*types.Var) {
 	// TODO(adonovan): this algorithm doesn't exclude ambiguous
 	// selections that match more than one field/method.
 	// types.NewSelectionSet should do that for us.

 	seen := make(map[*types.Var]bool) // for termination on recursive types

 	var visit func(T types.Type)
 	visit = func(T types.Type) {
 		if T, ok := deref(T).Underlying().(*types.Struct); ok {
 			for i := 0; i < T.NumFields(); i++ {
 				f := T.Field(i)
 				if seen[f] {
 					continue
 				}
 				seen[f] = true
 				fields = append(fields, f)
 				if f.Anonymous() {
 					visit(f.Type())
 				}
 			}
 		}
 	}
 	visit(T)

 	return fields
 }

 // resolveInvalid traverses the node of the AST that defines the scope
 // containing the declaration of obj, and attempts to find a user-friendly
 // name for its invalid type. The resulting Object and its Type are fake.
 func resolveInvalid(obj types.Object, node ast.Node, info *types.Info) types.Object {
 	// Construct a fake type for the object and return a fake object with this type.
 	formatResult := func(expr ast.Expr) types.Object {
 		var typename string
 		switch t := expr.(type) {
 		case *ast.SelectorExpr:
 			typename = fmt.Sprintf("%s.%s", t.X, t.Sel)
 		case *ast.Ident:
 			typename = t.String()
 		default:
 			return nil
 		}
 		typ := types.NewNamed(types.NewTypeName(token.NoPos, obj.Pkg(), typename, nil), types.Typ[types.Invalid], nil)
 		return types.NewVar(obj.Pos(), obj.Pkg(), obj.Name(), typ)
 	}
 	var resultExpr ast.Expr
 	ast.Inspect(node, func(node ast.Node) bool {
 		switch n := node.(type) {
 		case *ast.ValueSpec:
 			for _, name := range n.Names {
 				if info.Defs[name] == obj {
 					resultExpr = n.Type
 				}
 			}
 			return false
 		case *ast.Field: // This case handles parameters and results of a FuncDecl or FuncLit.
 			for _, name := range n.Names {
 				if info.Defs[name] == obj {
 					resultExpr = n.Type
 				}
 			}
 			return false
 		// TODO(rstambler): Handle range statements.
 		default:
 			return true
 		}
 	})
 	return formatResult(resultExpr)
 }

 func isPointer(T types.Type) bool {
 	_, ok := T.(*types.Pointer)
 	return ok
 }

 // deref returns a pointer's element type; otherwise it returns typ.
 func deref(typ types.Type) types.Type {
 	if p, ok := typ.Underlying().(*types.Pointer); ok {
 		return p.Elem()
 	}
 	return typ
 }

 func isTypeName(obj types.Object) bool {
 	_, ok := obj.(*types.TypeName)
 	return ok
 }

 func isFunc(obj types.Object) bool {
 	_, ok := obj.(*types.Func)
 	return ok
 }

 func isEmptyInterface(T types.Type) bool {
 	intf, _ := T.(*types.Interface)
 	return intf != nil && intf.NumMethods() == 0
 }

 // isSelector returns the enclosing *ast.SelectorExpr when pos is in the
 // selector.
 func enclosingSelector(path []ast.Node, pos token.Pos) *ast.SelectorExpr {
 	if len(path) == 0 {
 		return nil
 	}

 	if sel, ok := path[0].(*ast.SelectorExpr); ok {
 		return sel
 	}

 	if _, ok := path[0].(*ast.Ident); ok && len(path) > 1 {
 		if sel, ok := path[1].(*ast.SelectorExpr); ok && pos >= sel.Sel.Pos() {
 			return sel
 		}
 	}

 	return nil
 }

 // typeConversion returns the type being converted to if call is a type
 // conversion expression.
 func typeConversion(call *ast.CallExpr, info *types.Info) types.Type {
 	var ident *ast.Ident
 	switch expr := call.Fun.(type) {
 	case *ast.Ident:
 		ident = expr
 	case *ast.SelectorExpr:
 		ident = expr.Sel
 	default:
 		return nil
 	}

 	// Type conversion (e.g. "float64(foo)").
 	if fun, _ := info.ObjectOf(ident).(*types.TypeName); fun != nil {
 		return fun.Type()
 	}

 	return nil
 }

 func formatParams(tup *types.Tuple, variadic bool, qf types.Qualifier) []string {
 	params := make([]string, 0, tup.Len())
 	for i := 0; i < tup.Len(); i++ {
 		el := tup.At(i)
 		typ := types.TypeString(el.Type(), qf)

 		// Handle a variadic parameter (can only be the final parameter).
 		if variadic && i == tup.Len()-1 {
 			typ = strings.Replace(typ, "[]", "...", 1)
 		}

 		if el.Name() == "" {
 			params = append(params, typ)
 		} else {
 			params = append(params, el.Name()+" "+typ)
 		}
 	}
 	return params
 }

 func formatResults(tup *types.Tuple, qf types.Qualifier) ([]string, bool) {
 	var writeResultParens bool
 	results := make([]string, 0, tup.Len())
 	for i := 0; i < tup.Len(); i++ {
 		if i >= 1 {
 			writeResultParens = true
 		}
 		el := tup.At(i)
 		typ := types.TypeString(el.Type(), qf)

 		if el.Name() == "" {
 			results = append(results, typ)
 		} else {
 			if i == 0 {
 				writeResultParens = true
 			}
 			results = append(results, el.Name()+" "+typ)
 		}
 	}
 	return results, writeResultParens
 }

 // formatType returns the detail and kind for an object of type *types.TypeName.
 func formatType(typ types.Type, qf types.Qualifier) (detail string, kind protocol.CompletionItemKind) {
 	if types.IsInterface(typ) {
 		detail = "interface{...}"
 		kind = protocol.InterfaceCompletion
 	} else if _, ok := typ.(*types.Struct); ok {
 		detail = "struct{...}"
 		kind = protocol.StructCompletion
 	} else if typ != typ.Underlying() {
 		detail, kind = formatType(typ.Underlying(), qf)
 	} else {
 		detail = types.TypeString(typ, qf)
 		kind = protocol.ClassCompletion
 	}
 	return detail, kind
 }

 func formatFunction(params []string, results []string, writeResultParens bool) string {
 	var detail strings.Builder

 	detail.WriteByte('(')
 	for i, p := range params {
 		if i > 0 {
 			detail.WriteString(", ")
 		}
 		detail.WriteString(p)
 	}
 	detail.WriteByte(')')

 	// Add space between parameters and results.
 	if len(results) > 0 {
 		detail.WriteByte(' ')
 	}

 	if writeResultParens {
 		detail.WriteByte('(')
 	}
 	for i, p := range results {
 		if i > 0 {
 			detail.WriteString(", ")
 		}
 		detail.WriteString(p)
 	}
 	if writeResultParens {
 		detail.WriteByte(')')
 	}

 	return detail.String()
 }
	// 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"
	"fmt"
	"go/ast"
	"go/token"
	"go/types"
	"path/filepath"
	"regexp"
	"strings"

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

	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
	}

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

	// NarrowestCheckPackageHandle picks the "narrowest" package for a given file.
	//
	// By "narrowest" package, we mean the package with the fewest number of files
	// that includes the given file. This solves the problem of test variants,
	// as the test will have more files than the non-test package.
	func NarrowestCheckPackageHandle(handles []CheckPackageHandle) (CheckPackageHandle, error) {
	if len(handles) < 1 {
	return nil, errors.Errorf("no CheckPackageHandles")
	}
	result := handles[0]
	for _, handle := range handles[1:] {
	if result == nil \|\| len(handle.Files()) < len(result.Files()) {
	result = handle
	}
	}
	if result == nil {
	return nil, errors.Errorf("nil CheckPackageHandles have been returned")
	}
	return result, nil
	}

	// WidestCheckPackageHandle returns the CheckPackageHandle containing the most files.
	//
	// This is useful for something like diagnostics, where we'd prefer to offer diagnostics
	// for as many files as possible.
	func WidestCheckPackageHandle(handles []CheckPackageHandle) (CheckPackageHandle, error) {
	if len(handles) < 1 {
	return nil, errors.Errorf("no CheckPackageHandles")
	}
	result := handles[0]
	for _, handle := range handles[1:] {
	if result == nil \|\| len(handle.Files()) > len(result.Files()) {
	result = handle
	}
	}
	if result == nil {
	return nil, errors.Errorf("nil CheckPackageHandles have been returned")
	}
	return result, nil
	}

	func IsGenerated(ctx context.Context, view View, uri span.URI) bool {
	f, err := view.GetFile(ctx, uri)
	if err != nil {
	return false
	}
	ph := view.Session().Cache().ParseGoHandle(view.Snapshot().Handle(ctx, f), ParseHeader)
	parsed, _, _, err := ph.Parse(ctx)
	if err != nil {
	return false
	}
	tok := view.Session().Cache().FileSet().File(parsed.Pos())
	if tok == nil {
	return false
	}
	for _, commentGroup := range parsed.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(ctx context.Context, view View, m *protocol.ColumnMapper, n ast.Node) (protocol.Range, error) {
	mrng, err := nodeToMappedRange(ctx, view, m, n)
	if err != nil {
	return protocol.Range{}, err
	}
	return mrng.Range()
	}

	func objToMappedRange(ctx context.Context, v View, 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 point at the beginning of the declaration.
	if pkgName.Imported().Name() == pkgName.Name() {
	return nameToMappedRange(ctx, v, pkg, obj.Pos(), "")
	}
	}
	return nameToMappedRange(ctx, v, pkg, obj.Pos(), obj.Name())
	}

	func nameToMappedRange(ctx context.Context, v View, pkg Package, pos token.Pos, name string) (mappedRange, error) {
	return posToMappedRange(ctx, v, pkg, pos, pos+token.Pos(len(name)))
	}

	func nodeToMappedRange(ctx context.Context, view View, m *protocol.ColumnMapper, n ast.Node) (mappedRange, error) {
	return posToRange(ctx, view, m, n.Pos(), n.End())
	}

	func posToMappedRange(ctx context.Context, v View, pkg Package, pos, end token.Pos) (mappedRange, error) {
	m, err := posToMapper(ctx, v, pkg, pos)
	if err != nil {
	return mappedRange{}, err
	}
	return posToRange(ctx, v, m, pos, end)
	}

	func posToRange(ctx context.Context, view View, m *protocol.ColumnMapper, pos, end token.Pos) (mappedRange, error) {
	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 mappedRange{
	m: m,
	spanRange: span.NewRange(view.Session().Cache().FileSet(), pos, end),
	}, nil
	}

	func posToMapper(ctx context.Context, v View, pkg Package, pos token.Pos) (*protocol.ColumnMapper, error) {
	posn := v.Session().Cache().FileSet().Position(pos)
	ph, _, err := v.FindFileInPackage(ctx, span.FileURI(posn.Filename), pkg)
	if err != nil {
	return nil, err
	}
	_, m, _, err := ph.Cached()
	return m, err
	}

	// 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
	}
	// Fallback to detecting the language based on the file extension.
	switch filepath.Ext(filename) {
	case ".mod":
	return Mod
	case ".sum":
	return Sum
	default: // fallback to Go
	return Go
	}
	}

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

	// indexExprAtPos returns the index of the expression containing pos.
	func indexExprAtPos(pos token.Pos, args []ast.Expr) int {
	for i, expr := range args {
	if expr.Pos() <= pos && pos <= expr.End() {
	return i
	}
	}
	return len(args)
	}

	func exprAtPos(pos token.Pos, args []ast.Expr) ast.Expr {
	for _, expr := range args {
	if expr.Pos() <= pos && pos <= expr.End() {
	return expr
	}
	}
	return nil
	}

	// fieldSelections returns the set of fields that can
	// be selected from a value of type T.
	func fieldSelections(T types.Type) (fields []*types.Var) {
	// TODO(adonovan): this algorithm doesn't exclude ambiguous
	// selections that match more than one field/method.
	// types.NewSelectionSet should do that for us.

	seen := make(map[*types.Var]bool) // for termination on recursive types

	var visit func(T types.Type)
	visit = func(T types.Type) {
	if T, ok := deref(T).Underlying().(*types.Struct); ok {
	for i := 0; i < T.NumFields(); i++ {
	f := T.Field(i)
	if seen[f] {
	continue
	}
	seen[f] = true
	fields = append(fields, f)
	if f.Anonymous() {
	visit(f.Type())
	}
	}
	}
	}
	visit(T)

	return fields
	}

	// resolveInvalid traverses the node of the AST that defines the scope
	// containing the declaration of obj, and attempts to find a user-friendly
	// name for its invalid type. The resulting Object and its Type are fake.
	func resolveInvalid(obj types.Object, node ast.Node, info *types.Info) types.Object {
	// Construct a fake type for the object and return a fake object with this type.
	formatResult := func(expr ast.Expr) types.Object {
	var typename string
	switch t := expr.(type) {
	case *ast.SelectorExpr:
	typename = fmt.Sprintf("%s.%s", t.X, t.Sel)
	case *ast.Ident:
	typename = t.String()
	default:
	return nil
	}
	typ := types.NewNamed(types.NewTypeName(token.NoPos, obj.Pkg(), typename, nil), types.Typ[types.Invalid], nil)
	return types.NewVar(obj.Pos(), obj.Pkg(), obj.Name(), typ)
	}
	var resultExpr ast.Expr
	ast.Inspect(node, func(node ast.Node) bool {
	switch n := node.(type) {
	case *ast.ValueSpec:
	for _, name := range n.Names {
	if info.Defs[name] == obj {
	resultExpr = n.Type
	}
	}
	return false
	case *ast.Field: // This case handles parameters and results of a FuncDecl or FuncLit.
	for _, name := range n.Names {
	if info.Defs[name] == obj {
	resultExpr = n.Type
	}
	}
	return false
	// TODO(rstambler): Handle range statements.
	default:
	return true
	}
	})
	return formatResult(resultExpr)
	}

	func isPointer(T types.Type) bool {
	_, ok := T.(*types.Pointer)
	return ok
	}

	// deref returns a pointer's element type; otherwise it returns typ.
	func deref(typ types.Type) types.Type {
	if p, ok := typ.Underlying().(*types.Pointer); ok {
	return p.Elem()
	}
	return typ
	}

	func isTypeName(obj types.Object) bool {
	_, ok := obj.(*types.TypeName)
	return ok
	}

	func isFunc(obj types.Object) bool {
	_, ok := obj.(*types.Func)
	return ok
	}

	func isEmptyInterface(T types.Type) bool {
	intf, _ := T.(*types.Interface)
	return intf != nil && intf.NumMethods() == 0
	}

	// isSelector returns the enclosing *ast.SelectorExpr when pos is in the
	// selector.
	func enclosingSelector(path []ast.Node, pos token.Pos) *ast.SelectorExpr {
	if len(path) == 0 {
	return nil
	}

	if sel, ok := path[0].(*ast.SelectorExpr); ok {
	return sel
	}

	if _, ok := path[0].(*ast.Ident); ok && len(path) > 1 {
	if sel, ok := path[1].(*ast.SelectorExpr); ok && pos >= sel.Sel.Pos() {
	return sel
	}
	}

	return nil
	}

	// typeConversion returns the type being converted to if call is a type
	// conversion expression.
	func typeConversion(call ast.CallExpr, info types.Info) types.Type {
	var ident *ast.Ident
	switch expr := call.Fun.(type) {
	case *ast.Ident:
	ident = expr
	case *ast.SelectorExpr:
	ident = expr.Sel
	default:
	return nil
	}

	// Type conversion (e.g. "float64(foo)").
	if fun, _ := info.ObjectOf(ident).(*types.TypeName); fun != nil {
	return fun.Type()
	}

	return nil
	}

	func formatParams(tup *types.Tuple, variadic bool, qf types.Qualifier) []string {
	params := make([]string, 0, tup.Len())
	for i := 0; i < tup.Len(); i++ {
	el := tup.At(i)
	typ := types.TypeString(el.Type(), qf)

	// Handle a variadic parameter (can only be the final parameter).
	if variadic && i == tup.Len()-1 {
	typ = strings.Replace(typ, "[]", "...", 1)
	}

	if el.Name() == "" {
	params = append(params, typ)
	} else {
	params = append(params, el.Name()+" "+typ)
	}
	}
	return params
	}

	func formatResults(tup *types.Tuple, qf types.Qualifier) ([]string, bool) {
	var writeResultParens bool
	results := make([]string, 0, tup.Len())
	for i := 0; i < tup.Len(); i++ {
	if i >= 1 {
	writeResultParens = true
	}
	el := tup.At(i)
	typ := types.TypeString(el.Type(), qf)

	if el.Name() == "" {
	results = append(results, typ)
	} else {
	if i == 0 {
	writeResultParens = true
	}
	results = append(results, el.Name()+" "+typ)
	}
	}
	return results, writeResultParens
	}

	// formatType returns the detail and kind for an object of type *types.TypeName.
	func formatType(typ types.Type, qf types.Qualifier) (detail string, kind protocol.CompletionItemKind) {
	if types.IsInterface(typ) {
	detail = "interface{...}"
	kind = protocol.InterfaceCompletion
	} else if _, ok := typ.(*types.Struct); ok {
	detail = "struct{...}"
	kind = protocol.StructCompletion
	} else if typ != typ.Underlying() {
	detail, kind = formatType(typ.Underlying(), qf)
	} else {
	detail = types.TypeString(typ, qf)
	kind = protocol.ClassCompletion
	}
	return detail, kind
	}

	func formatFunction(params []string, results []string, writeResultParens bool) string {
	var detail strings.Builder

	detail.WriteByte('(')
	for i, p := range params {
	if i > 0 {
	detail.WriteString(", ")
	}
	detail.WriteString(p)
	}
	detail.WriteByte(')')

	// Add space between parameters and results.
	if len(results) > 0 {
	detail.WriteByte(' ')
	}

	if writeResultParens {
	detail.WriteByte('(')
	}
	for i, p := range results {
	if i > 0 {
	detail.WriteString(", ")
	}
	detail.WriteString(p)
	}
	if writeResultParens {
	detail.WriteByte(')')
	}

	return detail.String()
	}