gopls/internal/lsp/source/types_format.go - tools - Git at Google

 // Copyright 2020 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 (
 	"bytes"
 	"context"
 	"fmt"
 	"go/ast"
 	"go/doc"
 	"go/printer"
 	"go/token"
 	"go/types"
 	"strings"

 	"golang.org/x/tools/gopls/internal/lsp/protocol"
 	"golang.org/x/tools/internal/bug"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/event/tag"
 	"golang.org/x/tools/internal/typeparams"
 )

 // FormatType returns the detail and kind for a types.Type.
 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
 }

 type signature struct {
 	name, doc                   string
 	typeParams, params, results []string
 	variadic                    bool
 	needResultParens            bool
 }

 func (s *signature) Format() string {
 	var b strings.Builder
 	b.WriteByte('(')
 	for i, p := range s.params {
 		if i > 0 {
 			b.WriteString(", ")
 		}
 		b.WriteString(p)
 	}
 	b.WriteByte(')')

 	// Add space between parameters and results.
 	if len(s.results) > 0 {
 		b.WriteByte(' ')
 	}
 	if s.needResultParens {
 		b.WriteByte('(')
 	}
 	for i, r := range s.results {
 		if i > 0 {
 			b.WriteString(", ")
 		}
 		b.WriteString(r)
 	}
 	if s.needResultParens {
 		b.WriteByte(')')
 	}
 	return b.String()
 }

 func (s *signature) TypeParams() []string {
 	return s.typeParams
 }

 func (s *signature) Params() []string {
 	return s.params
 }

 // NewBuiltinSignature returns signature for the builtin object with a given
 // name, if a builtin object with the name exists.
 func NewBuiltinSignature(ctx context.Context, s Snapshot, name string) (*signature, error) {
 	fset := s.FileSet()
 	builtin, err := s.BuiltinFile(ctx)
 	if err != nil {
 		return nil, err
 	}
 	obj := builtin.File.Scope.Lookup(name)
 	if obj == nil {
 		return nil, fmt.Errorf("no builtin object for %s", name)
 	}
 	decl, ok := obj.Decl.(*ast.FuncDecl)
 	if !ok {
 		return nil, fmt.Errorf("no function declaration for builtin: %s", name)
 	}
 	if decl.Type == nil {
 		return nil, fmt.Errorf("no type for builtin decl %s", decl.Name)
 	}
 	var variadic bool
 	if decl.Type.Params.List != nil {
 		numParams := len(decl.Type.Params.List)
 		lastParam := decl.Type.Params.List[numParams-1]
 		if _, ok := lastParam.Type.(*ast.Ellipsis); ok {
 			variadic = true
 		}
 	}
 	params, _ := formatFieldList(ctx, fset, decl.Type.Params, variadic)
 	results, needResultParens := formatFieldList(ctx, fset, decl.Type.Results, false)
 	d := decl.Doc.Text()
 	switch s.View().Options().HoverKind {
 	case SynopsisDocumentation:
 		d = doc.Synopsis(d)
 	case NoDocumentation:
 		d = ""
 	}
 	return &signature{
 		doc:              d,
 		name:             name,
 		needResultParens: needResultParens,
 		params:           params,
 		results:          results,
 		variadic:         variadic,
 	}, nil
 }

 var replacer = strings.NewReplacer(
 	`ComplexType`, `complex128`,
 	`FloatType`, `float64`,
 	`IntegerType`, `int`,
 )

 func formatFieldList(ctx context.Context, fset *token.FileSet, list *ast.FieldList, variadic bool) ([]string, bool) {
 	if list == nil {
 		return nil, false
 	}
 	var writeResultParens bool
 	var result []string
 	for i := 0; i < len(list.List); i++ {
 		if i >= 1 {
 			writeResultParens = true
 		}
 		p := list.List[i]
 		cfg := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 4}
 		b := &bytes.Buffer{}
 		if err := cfg.Fprint(b, fset, p.Type); err != nil {
 			event.Error(ctx, "unable to print type", nil, tag.Type.Of(p.Type))
 			continue
 		}
 		typ := replacer.Replace(b.String())
 		if len(p.Names) == 0 {
 			result = append(result, typ)
 		}
 		for _, name := range p.Names {
 			if name.Name != "" {
 				if i == 0 {
 					writeResultParens = true
 				}
 				result = append(result, fmt.Sprintf("%s %s", name.Name, typ))
 			} else {
 				result = append(result, typ)
 			}
 		}
 	}
 	if variadic {
 		result[len(result)-1] = strings.Replace(result[len(result)-1], "[]", "...", 1)
 	}
 	return result, writeResultParens
 }

 // FormatTypeParams turns TypeParamList into its Go representation, such as:
 // [T, Y]. Note that it does not print constraints as this is mainly used for
 // formatting type params in method receivers.
 func FormatTypeParams(tparams *typeparams.TypeParamList) string {
 	if tparams == nil || tparams.Len() == 0 {
 		return ""
 	}
 	var buf bytes.Buffer
 	buf.WriteByte('[')
 	for i := 0; i < tparams.Len(); i++ {
 		if i > 0 {
 			buf.WriteString(", ")
 		}
 		buf.WriteString(tparams.At(i).Obj().Name())
 	}
 	buf.WriteByte(']')
 	return buf.String()
 }

 // NewSignature returns formatted signature for a types.Signature struct.
 func NewSignature(ctx context.Context, s Snapshot, pkg Package, srcFile *ast.File, sig *types.Signature, comment *ast.CommentGroup, qf types.Qualifier, mq MetadataQualifier) (*signature, error) {
 	var tparams []string
 	tpList := typeparams.ForSignature(sig)
 	for i := 0; i < tpList.Len(); i++ {
 		tparam := tpList.At(i)
 		// TODO: is it possible to reuse the logic from FormatVarType here?
 		s := tparam.Obj().Name() + " " + tparam.Constraint().String()
 		tparams = append(tparams, s)
 	}

 	params := make([]string, 0, sig.Params().Len())
 	for i := 0; i < sig.Params().Len(); i++ {
 		el := sig.Params().At(i)
 		typ, err := FormatVarType(ctx, s, pkg, srcFile, el, qf, mq)
 		if err != nil {
 			return nil, err
 		}
 		p := typ
 		if el.Name() != "" {
 			p = el.Name() + " " + typ
 		}
 		params = append(params, p)
 	}

 	var needResultParens bool
 	results := make([]string, 0, sig.Results().Len())
 	for i := 0; i < sig.Results().Len(); i++ {
 		if i >= 1 {
 			needResultParens = true
 		}
 		el := sig.Results().At(i)
 		typ, err := FormatVarType(ctx, s, pkg, srcFile, el, qf, mq)
 		if err != nil {
 			return nil, err
 		}
 		if el.Name() == "" {
 			results = append(results, typ)
 		} else {
 			if i == 0 {
 				needResultParens = true
 			}
 			results = append(results, el.Name()+" "+typ)
 		}
 	}
 	var d string
 	if comment != nil {
 		d = comment.Text()
 	}
 	switch s.View().Options().HoverKind {
 	case SynopsisDocumentation:
 		d = doc.Synopsis(d)
 	case NoDocumentation:
 		d = ""
 	}
 	return &signature{
 		doc:              d,
 		typeParams:       tparams,
 		params:           params,
 		results:          results,
 		variadic:         sig.Variadic(),
 		needResultParens: needResultParens,
 	}, nil
 }

 // FormatVarType formats a *types.Var, accounting for type aliases.
 // To do this, it looks in the AST of the file in which the object is declared.
 // On any errors, it always falls back to types.TypeString.
 //
 // TODO(rfindley): this function could return the actual name used in syntax,
 // for better parameter names.
 func FormatVarType(ctx context.Context, snapshot Snapshot, srcpkg Package, srcFile *ast.File, obj *types.Var, qf types.Qualifier, mq MetadataQualifier) (string, error) {
 	// TODO(rfindley): This looks wrong. The previous comment said:
 	// "If the given expr refers to a type parameter, then use the
 	// object's Type instead of the type parameter declaration. This helps
 	// format the instantiated type as opposed to the original undeclared
 	// generic type".
 	//
 	// But of course, if obj is a type param, we are formatting a generic type
 	// and not an instantiated type. Handling for instantiated types must be done
 	// at a higher level.
 	//
 	// Left this during refactoring in order to preserve pre-existing logic.
 	if typeparams.IsTypeParam(obj.Type()) {
 		return types.TypeString(obj.Type(), qf), nil
 	}

 	if obj.Pkg() == nil || !obj.Pos().IsValid() {
 		// This is defensive, though it is extremely unlikely we'll ever have a
 		// builtin var.
 		return types.TypeString(obj.Type(), qf), nil
 	}

 	targetpgf, pos, err := parseFull(ctx, snapshot, srcpkg, obj.Pos())
 	if err != nil {
 		return "", err // e.g. ctx cancelled
 	}

 	targetMeta := findFileInDepsMetadata(snapshot, srcpkg.Metadata(), targetpgf.URI)
 	if targetMeta == nil {
 		// If we have an object from type-checking, it should exist in a file in
 		// the forward transitive closure.
 		return "", bug.Errorf("failed to find file %q in deps of %q", targetpgf.URI, srcpkg.Metadata().ID)
 	}

 	decl, spec, field := FindDeclInfo([]*ast.File{targetpgf.File}, pos)

 	// We can't handle type parameters correctly, so we fall back on TypeString
 	// for parameterized decls.
 	if decl, _ := decl.(*ast.FuncDecl); decl != nil {
 		if typeparams.ForFuncType(decl.Type).NumFields() > 0 {
 			return types.TypeString(obj.Type(), qf), nil // in generic function
 		}
 		if decl.Recv != nil && len(decl.Recv.List) > 0 {
 			if x, _, _, _ := typeparams.UnpackIndexExpr(decl.Recv.List[0].Type); x != nil {
 				return types.TypeString(obj.Type(), qf), nil // in method of generic type
 			}
 		}
 	}
 	if spec, _ := spec.(*ast.TypeSpec); spec != nil && typeparams.ForTypeSpec(spec).NumFields() > 0 {
 		return types.TypeString(obj.Type(), qf), nil // in generic type decl
 	}

 	if field == nil {
 		// TODO(rfindley): we should never reach here from an ordinary var, so
 		// should probably return an error here.
 		return types.TypeString(obj.Type(), qf), nil
 	}
 	expr := field.Type

 	rq := requalifier(snapshot, targetpgf.File, targetMeta, mq)

 	// The type names in the AST may not be correctly qualified.
 	// Determine the package name to use based on the package that originated
 	// the query and the package in which the type is declared.
 	// We then qualify the value by cloning the AST node and editing it.
 	expr = qualifyTypeExpr(expr, rq)

 	// If the request came from a different package than the one in which the
 	// types are defined, we may need to modify the qualifiers.
 	return FormatNodeFile(targetpgf.Tok, expr), nil
 }

 // qualifyTypeExpr clones the type expression expr after re-qualifying type
 // names using the given function, which accepts the current syntactic
 // qualifier (possibly "" for unqualified idents), and returns a new qualifier
 // (again, possibly "" if the identifier should be unqualified).
 //
 // The resulting expression may be inaccurate: without type-checking we don't
 // properly account for "." imported identifiers or builtins.
 //
 // TODO(rfindley): add many more tests for this function.
 func qualifyTypeExpr(expr ast.Expr, qf func(string) string) ast.Expr {
 	switch expr := expr.(type) {
 	case *ast.ArrayType:
 		return &ast.ArrayType{
 			Lbrack: expr.Lbrack,
 			Elt:    qualifyTypeExpr(expr.Elt, qf),
 			Len:    expr.Len,
 		}

 	case *ast.BinaryExpr:
 		if expr.Op != token.OR {
 			return expr
 		}
 		return &ast.BinaryExpr{
 			X:     qualifyTypeExpr(expr.X, qf),
 			OpPos: expr.OpPos,
 			Op:    expr.Op,
 			Y:     qualifyTypeExpr(expr.Y, qf),
 		}

 	case *ast.ChanType:
 		return &ast.ChanType{
 			Arrow: expr.Arrow,
 			Begin: expr.Begin,
 			Dir:   expr.Dir,
 			Value: qualifyTypeExpr(expr.Value, qf),
 		}

 	case *ast.Ellipsis:
 		return &ast.Ellipsis{
 			Ellipsis: expr.Ellipsis,
 			Elt:      qualifyTypeExpr(expr.Elt, qf),
 		}

 	case *ast.FuncType:
 		return &ast.FuncType{
 			Func:    expr.Func,
 			Params:  qualifyFieldList(expr.Params, qf),
 			Results: qualifyFieldList(expr.Results, qf),
 		}

 	case *ast.Ident:
 		// Unqualified type (builtin, package local, or dot-imported).

 		// Don't qualify names that look like builtins.
 		//
 		// Without type-checking this may be inaccurate. It could be made accurate
 		// by doing syntactic object resolution for the entire package, but that
 		// does not seem worthwhile and we generally want to avoid using
 		// ast.Object, which may be inaccurate.
 		if obj := types.Universe.Lookup(expr.Name); obj != nil {
 			return expr
 		}

 		newName := qf("")
 		if newName != "" {
 			return &ast.SelectorExpr{
 				X: &ast.Ident{
 					NamePos: expr.Pos(),
 					Name:    newName,
 				},
 				Sel: expr,
 			}
 		}
 		return expr

 	case *ast.IndexExpr:
 		return &ast.IndexExpr{
 			X:      qualifyTypeExpr(expr.X, qf),
 			Lbrack: expr.Lbrack,
 			Index:  qualifyTypeExpr(expr.Index, qf),
 			Rbrack: expr.Rbrack,
 		}

 	case *typeparams.IndexListExpr:
 		indices := make([]ast.Expr, len(expr.Indices))
 		for i, idx := range expr.Indices {
 			indices[i] = qualifyTypeExpr(idx, qf)
 		}
 		return &typeparams.IndexListExpr{
 			X:       qualifyTypeExpr(expr.X, qf),
 			Lbrack:  expr.Lbrack,
 			Indices: indices,
 			Rbrack:  expr.Rbrack,
 		}

 	case *ast.InterfaceType:
 		return &ast.InterfaceType{
 			Interface:  expr.Interface,
 			Methods:    qualifyFieldList(expr.Methods, qf),
 			Incomplete: expr.Incomplete,
 		}

 	case *ast.MapType:
 		return &ast.MapType{
 			Map:   expr.Map,
 			Key:   qualifyTypeExpr(expr.Key, qf),
 			Value: qualifyTypeExpr(expr.Value, qf),
 		}

 	case *ast.ParenExpr:
 		return &ast.ParenExpr{
 			Lparen: expr.Lparen,
 			Rparen: expr.Rparen,
 			X:      qualifyTypeExpr(expr.X, qf),
 		}

 	case *ast.SelectorExpr:
 		if id, ok := expr.X.(*ast.Ident); ok {
 			// qualified type
 			newName := qf(id.Name)
 			if newName == "" {
 				return expr.Sel
 			}
 			return &ast.SelectorExpr{
 				X: &ast.Ident{
 					NamePos: id.NamePos,
 					Name:    newName,
 				},
 				Sel: expr.Sel,
 			}
 		}
 		return expr

 	case *ast.StarExpr:
 		return &ast.StarExpr{
 			Star: expr.Star,
 			X:    qualifyTypeExpr(expr.X, qf),
 		}

 	case *ast.StructType:
 		return &ast.StructType{
 			Struct:     expr.Struct,
 			Fields:     qualifyFieldList(expr.Fields, qf),
 			Incomplete: expr.Incomplete,
 		}

 	default:
 		return expr
 	}
 }

 func qualifyFieldList(fl *ast.FieldList, qf func(string) string) *ast.FieldList {
 	if fl == nil {
 		return nil
 	}
 	if fl.List == nil {
 		return &ast.FieldList{
 			Closing: fl.Closing,
 			Opening: fl.Opening,
 		}
 	}
 	list := make([]*ast.Field, 0, len(fl.List))
 	for _, f := range fl.List {
 		list = append(list, &ast.Field{
 			Comment: f.Comment,
 			Doc:     f.Doc,
 			Names:   f.Names,
 			Tag:     f.Tag,
 			Type:    qualifyTypeExpr(f.Type, qf),
 		})
 	}
 	return &ast.FieldList{
 		Closing: fl.Closing,
 		Opening: fl.Opening,
 		List:    list,
 	}
 }
	// Copyright 2020 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 (
	"bytes"
	"context"
	"fmt"
	"go/ast"
	"go/doc"
	"go/printer"
	"go/token"
	"go/types"
	"strings"

	"golang.org/x/tools/gopls/internal/lsp/protocol"
	"golang.org/x/tools/internal/bug"
	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/event/tag"
	"golang.org/x/tools/internal/typeparams"
	)

	// FormatType returns the detail and kind for a types.Type.
	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
	}

	type signature struct {
	name, doc string
	typeParams, params, results []string
	variadic bool
	needResultParens bool
	}

	func (s *signature) Format() string {
	var b strings.Builder
	b.WriteByte('(')
	for i, p := range s.params {
	if i > 0 {
	b.WriteString(", ")
	}
	b.WriteString(p)
	}
	b.WriteByte(')')

	// Add space between parameters and results.
	if len(s.results) > 0 {
	b.WriteByte(' ')
	}
	if s.needResultParens {
	b.WriteByte('(')
	}
	for i, r := range s.results {
	if i > 0 {
	b.WriteString(", ")
	}
	b.WriteString(r)
	}
	if s.needResultParens {
	b.WriteByte(')')
	}
	return b.String()
	}

	func (s *signature) TypeParams() []string {
	return s.typeParams
	}

	func (s *signature) Params() []string {
	return s.params
	}

	// NewBuiltinSignature returns signature for the builtin object with a given
	// name, if a builtin object with the name exists.
	func NewBuiltinSignature(ctx context.Context, s Snapshot, name string) (*signature, error) {
	fset := s.FileSet()
	builtin, err := s.BuiltinFile(ctx)
	if err != nil {
	return nil, err
	}
	obj := builtin.File.Scope.Lookup(name)
	if obj == nil {
	return nil, fmt.Errorf("no builtin object for %s", name)
	}
	decl, ok := obj.Decl.(*ast.FuncDecl)
	if !ok {
	return nil, fmt.Errorf("no function declaration for builtin: %s", name)
	}
	if decl.Type == nil {
	return nil, fmt.Errorf("no type for builtin decl %s", decl.Name)
	}
	var variadic bool
	if decl.Type.Params.List != nil {
	numParams := len(decl.Type.Params.List)
	lastParam := decl.Type.Params.List[numParams-1]
	if _, ok := lastParam.Type.(*ast.Ellipsis); ok {
	variadic = true
	}
	}
	params, _ := formatFieldList(ctx, fset, decl.Type.Params, variadic)
	results, needResultParens := formatFieldList(ctx, fset, decl.Type.Results, false)
	d := decl.Doc.Text()
	switch s.View().Options().HoverKind {
	case SynopsisDocumentation:
	d = doc.Synopsis(d)
	case NoDocumentation:
	d = ""
	}
	return &signature{
	doc: d,
	name: name,
	needResultParens: needResultParens,
	params: params,
	results: results,
	variadic: variadic,
	}, nil
	}

	var replacer = strings.NewReplacer(
	`ComplexType`, `complex128`,
	`FloatType`, `float64`,
	`IntegerType`, `int`,
	)

	func formatFieldList(ctx context.Context, fset token.FileSet, list ast.FieldList, variadic bool) ([]string, bool) {
	if list == nil {
	return nil, false
	}
	var writeResultParens bool
	var result []string
	for i := 0; i < len(list.List); i++ {
	if i >= 1 {
	writeResultParens = true
	}
	p := list.List[i]
	cfg := printer.Config{Mode: printer.UseSpaces \| printer.TabIndent, Tabwidth: 4}
	b := &bytes.Buffer{}
	if err := cfg.Fprint(b, fset, p.Type); err != nil {
	event.Error(ctx, "unable to print type", nil, tag.Type.Of(p.Type))
	continue
	}
	typ := replacer.Replace(b.String())
	if len(p.Names) == 0 {
	result = append(result, typ)
	}
	for _, name := range p.Names {
	if name.Name != "" {
	if i == 0 {
	writeResultParens = true
	}
	result = append(result, fmt.Sprintf("%s %s", name.Name, typ))
	} else {
	result = append(result, typ)
	}
	}
	}
	if variadic {
	result[len(result)-1] = strings.Replace(result[len(result)-1], "[]", "...", 1)
	}
	return result, writeResultParens
	}

	// FormatTypeParams turns TypeParamList into its Go representation, such as:
	// [T, Y]. Note that it does not print constraints as this is mainly used for
	// formatting type params in method receivers.
	func FormatTypeParams(tparams *typeparams.TypeParamList) string {
	if tparams == nil \|\| tparams.Len() == 0 {
	return ""
	}
	var buf bytes.Buffer
	buf.WriteByte('[')
	for i := 0; i < tparams.Len(); i++ {
	if i > 0 {
	buf.WriteString(", ")
	}
	buf.WriteString(tparams.At(i).Obj().Name())
	}
	buf.WriteByte(']')
	return buf.String()
	}

	// NewSignature returns formatted signature for a types.Signature struct.
	func NewSignature(ctx context.Context, s Snapshot, pkg Package, srcFile ast.File, sig types.Signature, comment ast.CommentGroup, qf types.Qualifier, mq MetadataQualifier) (signature, error) {
	var tparams []string
	tpList := typeparams.ForSignature(sig)
	for i := 0; i < tpList.Len(); i++ {
	tparam := tpList.At(i)
	// TODO: is it possible to reuse the logic from FormatVarType here?
	s := tparam.Obj().Name() + " " + tparam.Constraint().String()
	tparams = append(tparams, s)
	}

	params := make([]string, 0, sig.Params().Len())
	for i := 0; i < sig.Params().Len(); i++ {
	el := sig.Params().At(i)
	typ, err := FormatVarType(ctx, s, pkg, srcFile, el, qf, mq)
	if err != nil {
	return nil, err
	}
	p := typ
	if el.Name() != "" {
	p = el.Name() + " " + typ
	}
	params = append(params, p)
	}

	var needResultParens bool
	results := make([]string, 0, sig.Results().Len())
	for i := 0; i < sig.Results().Len(); i++ {
	if i >= 1 {
	needResultParens = true
	}
	el := sig.Results().At(i)
	typ, err := FormatVarType(ctx, s, pkg, srcFile, el, qf, mq)
	if err != nil {
	return nil, err
	}
	if el.Name() == "" {
	results = append(results, typ)
	} else {
	if i == 0 {
	needResultParens = true
	}
	results = append(results, el.Name()+" "+typ)
	}
	}
	var d string
	if comment != nil {
	d = comment.Text()
	}
	switch s.View().Options().HoverKind {
	case SynopsisDocumentation:
	d = doc.Synopsis(d)
	case NoDocumentation:
	d = ""
	}
	return &signature{
	doc: d,
	typeParams: tparams,
	params: params,
	results: results,
	variadic: sig.Variadic(),
	needResultParens: needResultParens,
	}, nil
	}

	// FormatVarType formats a *types.Var, accounting for type aliases.
	// To do this, it looks in the AST of the file in which the object is declared.
	// On any errors, it always falls back to types.TypeString.
	//
	// TODO(rfindley): this function could return the actual name used in syntax,
	// for better parameter names.
	func FormatVarType(ctx context.Context, snapshot Snapshot, srcpkg Package, srcFile ast.File, obj types.Var, qf types.Qualifier, mq MetadataQualifier) (string, error) {
	// TODO(rfindley): This looks wrong. The previous comment said:
	// "If the given expr refers to a type parameter, then use the
	// object's Type instead of the type parameter declaration. This helps
	// format the instantiated type as opposed to the original undeclared
	// generic type".
	//
	// But of course, if obj is a type param, we are formatting a generic type
	// and not an instantiated type. Handling for instantiated types must be done
	// at a higher level.
	//
	// Left this during refactoring in order to preserve pre-existing logic.
	if typeparams.IsTypeParam(obj.Type()) {
	return types.TypeString(obj.Type(), qf), nil
	}

	if obj.Pkg() == nil \|\| !obj.Pos().IsValid() {
	// This is defensive, though it is extremely unlikely we'll ever have a
	// builtin var.
	return types.TypeString(obj.Type(), qf), nil
	}

	targetpgf, pos, err := parseFull(ctx, snapshot, srcpkg, obj.Pos())
	if err != nil {
	return "", err // e.g. ctx cancelled
	}

	targetMeta := findFileInDepsMetadata(snapshot, srcpkg.Metadata(), targetpgf.URI)
	if targetMeta == nil {
	// If we have an object from type-checking, it should exist in a file in
	// the forward transitive closure.
	return "", bug.Errorf("failed to find file %q in deps of %q", targetpgf.URI, srcpkg.Metadata().ID)
	}

	decl, spec, field := FindDeclInfo([]*ast.File{targetpgf.File}, pos)

	// We can't handle type parameters correctly, so we fall back on TypeString
	// for parameterized decls.
	if decl, _ := decl.(*ast.FuncDecl); decl != nil {
	if typeparams.ForFuncType(decl.Type).NumFields() > 0 {
	return types.TypeString(obj.Type(), qf), nil // in generic function
	}
	if decl.Recv != nil && len(decl.Recv.List) > 0 {
	if x, _, _, _ := typeparams.UnpackIndexExpr(decl.Recv.List[0].Type); x != nil {
	return types.TypeString(obj.Type(), qf), nil // in method of generic type
	}
	}
	}
	if spec, _ := spec.(*ast.TypeSpec); spec != nil && typeparams.ForTypeSpec(spec).NumFields() > 0 {
	return types.TypeString(obj.Type(), qf), nil // in generic type decl
	}

	if field == nil {
	// TODO(rfindley): we should never reach here from an ordinary var, so
	// should probably return an error here.
	return types.TypeString(obj.Type(), qf), nil
	}
	expr := field.Type

	rq := requalifier(snapshot, targetpgf.File, targetMeta, mq)

	// The type names in the AST may not be correctly qualified.
	// Determine the package name to use based on the package that originated
	// the query and the package in which the type is declared.
	// We then qualify the value by cloning the AST node and editing it.
	expr = qualifyTypeExpr(expr, rq)

	// If the request came from a different package than the one in which the
	// types are defined, we may need to modify the qualifiers.
	return FormatNodeFile(targetpgf.Tok, expr), nil
	}

	// qualifyTypeExpr clones the type expression expr after re-qualifying type
	// names using the given function, which accepts the current syntactic
	// qualifier (possibly "" for unqualified idents), and returns a new qualifier
	// (again, possibly "" if the identifier should be unqualified).
	//
	// The resulting expression may be inaccurate: without type-checking we don't
	// properly account for "." imported identifiers or builtins.
	//
	// TODO(rfindley): add many more tests for this function.
	func qualifyTypeExpr(expr ast.Expr, qf func(string) string) ast.Expr {
	switch expr := expr.(type) {
	case *ast.ArrayType:
	return &ast.ArrayType{
	Lbrack: expr.Lbrack,
	Elt: qualifyTypeExpr(expr.Elt, qf),
	Len: expr.Len,
	}

	case *ast.BinaryExpr:
	if expr.Op != token.OR {
	return expr
	}
	return &ast.BinaryExpr{
	X: qualifyTypeExpr(expr.X, qf),
	OpPos: expr.OpPos,
	Op: expr.Op,
	Y: qualifyTypeExpr(expr.Y, qf),
	}

	case *ast.ChanType:
	return &ast.ChanType{
	Arrow: expr.Arrow,
	Begin: expr.Begin,
	Dir: expr.Dir,
	Value: qualifyTypeExpr(expr.Value, qf),
	}

	case *ast.Ellipsis:
	return &ast.Ellipsis{
	Ellipsis: expr.Ellipsis,
	Elt: qualifyTypeExpr(expr.Elt, qf),
	}

	case *ast.FuncType:
	return &ast.FuncType{
	Func: expr.Func,
	Params: qualifyFieldList(expr.Params, qf),
	Results: qualifyFieldList(expr.Results, qf),
	}

	case *ast.Ident:
	// Unqualified type (builtin, package local, or dot-imported).

	// Don't qualify names that look like builtins.
	//
	// Without type-checking this may be inaccurate. It could be made accurate
	// by doing syntactic object resolution for the entire package, but that
	// does not seem worthwhile and we generally want to avoid using
	// ast.Object, which may be inaccurate.
	if obj := types.Universe.Lookup(expr.Name); obj != nil {
	return expr
	}

	newName := qf("")
	if newName != "" {
	return &ast.SelectorExpr{
	X: &ast.Ident{
	NamePos: expr.Pos(),
	Name: newName,
	},
	Sel: expr,
	}
	}
	return expr

	case *ast.IndexExpr:
	return &ast.IndexExpr{
	X: qualifyTypeExpr(expr.X, qf),
	Lbrack: expr.Lbrack,
	Index: qualifyTypeExpr(expr.Index, qf),
	Rbrack: expr.Rbrack,
	}

	case *typeparams.IndexListExpr:
	indices := make([]ast.Expr, len(expr.Indices))
	for i, idx := range expr.Indices {
	indices[i] = qualifyTypeExpr(idx, qf)
	}
	return &typeparams.IndexListExpr{
	X: qualifyTypeExpr(expr.X, qf),
	Lbrack: expr.Lbrack,
	Indices: indices,
	Rbrack: expr.Rbrack,
	}

	case *ast.InterfaceType:
	return &ast.InterfaceType{
	Interface: expr.Interface,
	Methods: qualifyFieldList(expr.Methods, qf),
	Incomplete: expr.Incomplete,
	}

	case *ast.MapType:
	return &ast.MapType{
	Map: expr.Map,
	Key: qualifyTypeExpr(expr.Key, qf),
	Value: qualifyTypeExpr(expr.Value, qf),
	}

	case *ast.ParenExpr:
	return &ast.ParenExpr{
	Lparen: expr.Lparen,
	Rparen: expr.Rparen,
	X: qualifyTypeExpr(expr.X, qf),
	}

	case *ast.SelectorExpr:
	if id, ok := expr.X.(*ast.Ident); ok {
	// qualified type
	newName := qf(id.Name)
	if newName == "" {
	return expr.Sel
	}
	return &ast.SelectorExpr{
	X: &ast.Ident{
	NamePos: id.NamePos,
	Name: newName,
	},
	Sel: expr.Sel,
	}
	}
	return expr

	case *ast.StarExpr:
	return &ast.StarExpr{
	Star: expr.Star,
	X: qualifyTypeExpr(expr.X, qf),
	}

	case *ast.StructType:
	return &ast.StructType{
	Struct: expr.Struct,
	Fields: qualifyFieldList(expr.Fields, qf),
	Incomplete: expr.Incomplete,
	}

	default:
	return expr
	}
	}

	func qualifyFieldList(fl ast.FieldList, qf func(string) string) ast.FieldList {
	if fl == nil {
	return nil
	}
	if fl.List == nil {
	return &ast.FieldList{
	Closing: fl.Closing,
	Opening: fl.Opening,
	}
	}
	list := make([]*ast.Field, 0, len(fl.List))
	for _, f := range fl.List {
	list = append(list, &ast.Field{
	Comment: f.Comment,
	Doc: f.Doc,
	Names: f.Names,
	Tag: f.Tag,
	Type: qualifyTypeExpr(f.Type, qf),
	})
	}
	return &ast.FieldList{
	Closing: fl.Closing,
	Opening: fl.Opening,
	List: list,
	}
	}