src/go/types/typestring.go - go - Git at Google

 // Copyright 2013 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.

 // This file implements printing of types.

 package types

 import (
 	"bytes"
 	"fmt"
 	"go/token"
 	"unicode/utf8"
 )

 // A Qualifier controls how named package-level objects are printed in
 // calls to TypeString, ObjectString, and SelectionString.
 //
 // These three formatting routines call the Qualifier for each
 // package-level object O, and if the Qualifier returns a non-empty
 // string p, the object is printed in the form p.O.
 // If it returns an empty string, only the object name O is printed.
 //
 // Using a nil Qualifier is equivalent to using (*Package).Path: the
 // object is qualified by the import path, e.g., "encoding/json.Marshal".
 //
 type Qualifier func(*Package) string

 // RelativeTo returns a Qualifier that fully qualifies members of
 // all packages other than pkg.
 func RelativeTo(pkg *Package) Qualifier {
 	if pkg == nil {
 		return nil
 	}
 	return func(other *Package) string {
 		if pkg == other {
 			return "" // same package; unqualified
 		}
 		return other.Path()
 	}
 }

 // If gcCompatibilityMode is set, printing of types is modified
 // to match the representation of some types in the gc compiler:
 //
 //	- byte and rune lose their alias name and simply stand for
 //	  uint8 and int32 respectively
 //	- embedded interfaces get flattened (the embedding info is lost,
 //	  and certain recursive interface types cannot be printed anymore)
 //
 // This makes it easier to compare packages computed with the type-
 // checker vs packages imported from gc export data.
 //
 // Caution: This flag affects all uses of WriteType, globally.
 // It is only provided for testing in conjunction with
 // gc-generated data.
 //
 // This flag is exported in the x/tools/go/types package. We don't
 // need it at the moment in the std repo and so we don't export it
 // anymore. We should eventually try to remove it altogether.
 // TODO(gri) remove this
 var gcCompatibilityMode bool

 // TypeString returns the string representation of typ.
 // The Qualifier controls the printing of
 // package-level objects, and may be nil.
 func TypeString(typ Type, qf Qualifier) string {
 	var buf bytes.Buffer
 	WriteType(&buf, typ, qf)
 	return buf.String()
 }

 // WriteType writes the string representation of typ to buf.
 // The Qualifier controls the printing of
 // package-level objects, and may be nil.
 func WriteType(buf *bytes.Buffer, typ Type, qf Qualifier) {
 	writeType(buf, typ, qf, make([]Type, 0, 8))
 }

 // instanceMarker is the prefix for an instantiated type
 // in "non-evaluated" instance form.
 const instanceMarker = '#'

 func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
 	// Theoretically, this is a quadratic lookup algorithm, but in
 	// practice deeply nested composite types with unnamed component
 	// types are uncommon. This code is likely more efficient than
 	// using a map.
 	for _, t := range visited {
 		if t == typ {
 			fmt.Fprintf(buf, "○%T", goTypeName(typ)) // cycle to typ
 			return
 		}
 	}
 	visited = append(visited, typ)

 	switch t := typ.(type) {
 	case nil:
 		buf.WriteString("<nil>")

 	case *Basic:
 		// exported basic types go into package unsafe
 		// (currently this is just unsafe.Pointer)
 		if token.IsExported(t.name) {
 			if obj, _ := Unsafe.scope.Lookup(t.name).(*TypeName); obj != nil {
 				writeTypeName(buf, obj, qf)
 				break
 			}
 		}

 		if gcCompatibilityMode {
 			// forget the alias names
 			switch t.kind {
 			case Byte:
 				t = Typ[Uint8]
 			case Rune:
 				t = Typ[Int32]
 			}
 		}
 		buf.WriteString(t.name)

 	case *Array:
 		fmt.Fprintf(buf, "[%d]", t.len)
 		writeType(buf, t.elem, qf, visited)

 	case *Slice:
 		buf.WriteString("[]")
 		writeType(buf, t.elem, qf, visited)

 	case *Struct:
 		buf.WriteString("struct{")
 		for i, f := range t.fields {
 			if i > 0 {
 				buf.WriteString("; ")
 			}
 			// This doesn't do the right thing for embedded type
 			// aliases where we should print the alias name, not
 			// the aliased type (see issue #44410).
 			if !f.embedded {
 				buf.WriteString(f.name)
 				buf.WriteByte(' ')
 			}
 			writeType(buf, f.typ, qf, visited)
 			if tag := t.Tag(i); tag != "" {
 				fmt.Fprintf(buf, " %q", tag)
 			}
 		}
 		buf.WriteByte('}')

 	case *Pointer:
 		buf.WriteByte('*')
 		writeType(buf, t.base, qf, visited)

 	case *Tuple:
 		writeTuple(buf, t, false, qf, visited)

 	case *Signature:
 		buf.WriteString("func")
 		writeSignature(buf, t, qf, visited)

 	case *_Sum:
 		for i, t := range t.types {
 			if i > 0 {
 				buf.WriteString(", ")
 			}
 			writeType(buf, t, qf, visited)
 		}

 	case *Interface:
 		// We write the source-level methods and embedded types rather
 		// than the actual method set since resolved method signatures
 		// may have non-printable cycles if parameters have embedded
 		// interface types that (directly or indirectly) embed the
 		// current interface. For instance, consider the result type
 		// of m:
 		//
 		//     type T interface{
 		//         m() interface{ T }
 		//     }
 		//
 		buf.WriteString("interface{")
 		empty := true
 		if gcCompatibilityMode {
 			// print flattened interface
 			// (useful to compare against gc-generated interfaces)
 			for i, m := range t.allMethods {
 				if i > 0 {
 					buf.WriteString("; ")
 				}
 				buf.WriteString(m.name)
 				writeSignature(buf, m.typ.(*Signature), qf, visited)
 				empty = false
 			}
 			if !empty && t.allTypes != nil {
 				buf.WriteString("; ")
 			}
 			if t.allTypes != nil {
 				buf.WriteString("type ")
 				writeType(buf, t.allTypes, qf, visited)
 			}
 		} else {
 			// print explicit interface methods and embedded types
 			for i, m := range t.methods {
 				if i > 0 {
 					buf.WriteString("; ")
 				}
 				buf.WriteString(m.name)
 				writeSignature(buf, m.typ.(*Signature), qf, visited)
 				empty = false
 			}
 			if !empty && t.types != nil {
 				buf.WriteString("; ")
 			}
 			if t.types != nil {
 				buf.WriteString("type ")
 				writeType(buf, t.types, qf, visited)
 				empty = false
 			}
 			if !empty && len(t.embeddeds) > 0 {
 				buf.WriteString("; ")
 			}
 			for i, typ := range t.embeddeds {
 				if i > 0 {
 					buf.WriteString("; ")
 				}
 				writeType(buf, typ, qf, visited)
 				empty = false
 			}
 		}
 		if t.allMethods == nil || len(t.methods) > len(t.allMethods) {
 			if !empty {
 				buf.WriteByte(' ')
 			}
 			buf.WriteString("/* incomplete */")
 		}
 		buf.WriteByte('}')

 	case *Map:
 		buf.WriteString("map[")
 		writeType(buf, t.key, qf, visited)
 		buf.WriteByte(']')
 		writeType(buf, t.elem, qf, visited)

 	case *Chan:
 		var s string
 		var parens bool
 		switch t.dir {
 		case SendRecv:
 			s = "chan "
 			// chan (<-chan T) requires parentheses
 			if c, _ := t.elem.(*Chan); c != nil && c.dir == RecvOnly {
 				parens = true
 			}
 		case SendOnly:
 			s = "chan<- "
 		case RecvOnly:
 			s = "<-chan "
 		default:
 			panic("unreachable")
 		}
 		buf.WriteString(s)
 		if parens {
 			buf.WriteByte('(')
 		}
 		writeType(buf, t.elem, qf, visited)
 		if parens {
 			buf.WriteByte(')')
 		}

 	case *Named:
 		writeTypeName(buf, t.obj, qf)
 		if t.targs != nil {
 			// instantiated type
 			buf.WriteByte('[')
 			writeTypeList(buf, t.targs, qf, visited)
 			buf.WriteByte(']')
 		} else if t.tparams != nil {
 			// parameterized type
 			writeTParamList(buf, t.tparams, qf, visited)
 		}

 	case *_TypeParam:
 		s := "?"
 		if t.obj != nil {
 			s = t.obj.name
 		}
 		buf.WriteString(s + subscript(t.id))

 	case *instance:
 		buf.WriteByte(instanceMarker) // indicate "non-evaluated" syntactic instance
 		writeTypeName(buf, t.base.obj, qf)
 		buf.WriteByte('[')
 		writeTypeList(buf, t.targs, qf, visited)
 		buf.WriteByte(']')

 	case *bottom:
 		buf.WriteString("⊥")

 	case *top:
 		buf.WriteString("⊤")

 	default:
 		// For externally defined implementations of Type.
 		buf.WriteString(t.String())
 	}
 }

 func writeTypeList(buf *bytes.Buffer, list []Type, qf Qualifier, visited []Type) {
 	for i, typ := range list {
 		if i > 0 {
 			buf.WriteString(", ")
 		}
 		writeType(buf, typ, qf, visited)
 	}
 }

 func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited []Type) {
 	// TODO(rFindley) compare this with the corresponding implementation in types2
 	buf.WriteString("[")
 	var prev Type
 	for i, p := range list {
 		// TODO(rFindley) support 'any' sugar here.
 		var b Type = &emptyInterface
 		if t, _ := p.typ.(*_TypeParam); t != nil && t.bound != nil {
 			b = t.bound
 		}
 		if i > 0 {
 			if b != prev {
 				// type bound changed - write previous one before advancing
 				buf.WriteByte(' ')
 				writeType(buf, prev, qf, visited)
 			}
 			buf.WriteString(", ")
 		}
 		prev = b

 		if t, _ := p.typ.(*_TypeParam); t != nil {
 			writeType(buf, t, qf, visited)
 		} else {
 			buf.WriteString(p.name)
 		}
 	}
 	if prev != nil {
 		buf.WriteByte(' ')
 		writeType(buf, prev, qf, visited)
 	}
 	buf.WriteByte(']')
 }

 func writeTypeName(buf *bytes.Buffer, obj *TypeName, qf Qualifier) {
 	s := "<Named w/o object>"
 	if obj != nil {
 		if obj.pkg != nil {
 			writePackage(buf, obj.pkg, qf)
 		}
 		// TODO(gri): function-local named types should be displayed
 		// differently from named types at package level to avoid
 		// ambiguity.
 		s = obj.name
 	}
 	buf.WriteString(s)
 }

 func writeTuple(buf *bytes.Buffer, tup *Tuple, variadic bool, qf Qualifier, visited []Type) {
 	buf.WriteByte('(')
 	if tup != nil {
 		for i, v := range tup.vars {
 			if i > 0 {
 				buf.WriteString(", ")
 			}
 			if v.name != "" {
 				buf.WriteString(v.name)
 				buf.WriteByte(' ')
 			}
 			typ := v.typ
 			if variadic && i == len(tup.vars)-1 {
 				if s, ok := typ.(*Slice); ok {
 					buf.WriteString("...")
 					typ = s.elem
 				} else {
 					// special case:
 					// append(s, "foo"...) leads to signature func([]byte, string...)
 					if t := asBasic(typ); t == nil || t.kind != String {
 						panic("internal error: string type expected")
 					}
 					writeType(buf, typ, qf, visited)
 					buf.WriteString("...")
 					continue
 				}
 			}
 			writeType(buf, typ, qf, visited)
 		}
 	}
 	buf.WriteByte(')')
 }

 // WriteSignature writes the representation of the signature sig to buf,
 // without a leading "func" keyword.
 // The Qualifier controls the printing of
 // package-level objects, and may be nil.
 func WriteSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier) {
 	writeSignature(buf, sig, qf, make([]Type, 0, 8))
 }

 func writeSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier, visited []Type) {
 	if sig.tparams != nil {
 		writeTParamList(buf, sig.tparams, qf, visited)
 	}

 	writeTuple(buf, sig.params, sig.variadic, qf, visited)

 	n := sig.results.Len()
 	if n == 0 {
 		// no result
 		return
 	}

 	buf.WriteByte(' ')
 	if n == 1 && sig.results.vars[0].name == "" {
 		// single unnamed result
 		writeType(buf, sig.results.vars[0].typ, qf, visited)
 		return
 	}

 	// multiple or named result(s)
 	writeTuple(buf, sig.results, false, qf, visited)
 }

 // subscript returns the decimal (utf8) representation of x using subscript digits.
 func subscript(x uint64) string {
 	const w = len("₀") // all digits 0...9 have the same utf8 width
 	var buf [32 * w]byte
 	i := len(buf)
 	for {
 		i -= w
 		utf8.EncodeRune(buf[i:], '₀'+rune(x%10)) // '₀' == U+2080
 		x /= 10
 		if x == 0 {
 			break
 		}
 	}
 	return string(buf[i:])
 }
	// Copyright 2013 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.

	// This file implements printing of types.

	package types

	import (
	"bytes"
	"fmt"
	"go/token"
	"unicode/utf8"
	)

	// A Qualifier controls how named package-level objects are printed in
	// calls to TypeString, ObjectString, and SelectionString.
	//
	// These three formatting routines call the Qualifier for each
	// package-level object O, and if the Qualifier returns a non-empty
	// string p, the object is printed in the form p.O.
	// If it returns an empty string, only the object name O is printed.
	//
	// Using a nil Qualifier is equivalent to using (*Package).Path: the
	// object is qualified by the import path, e.g., "encoding/json.Marshal".
	//
	type Qualifier func(*Package) string

	// RelativeTo returns a Qualifier that fully qualifies members of
	// all packages other than pkg.
	func RelativeTo(pkg *Package) Qualifier {
	if pkg == nil {
	return nil
	}
	return func(other *Package) string {
	if pkg == other {
	return "" // same package; unqualified
	}
	return other.Path()
	}
	}

	// If gcCompatibilityMode is set, printing of types is modified
	// to match the representation of some types in the gc compiler:
	//
	// - byte and rune lose their alias name and simply stand for
	// uint8 and int32 respectively
	// - embedded interfaces get flattened (the embedding info is lost,
	// and certain recursive interface types cannot be printed anymore)
	//
	// This makes it easier to compare packages computed with the type-
	// checker vs packages imported from gc export data.
	//
	// Caution: This flag affects all uses of WriteType, globally.
	// It is only provided for testing in conjunction with
	// gc-generated data.
	//
	// This flag is exported in the x/tools/go/types package. We don't
	// need it at the moment in the std repo and so we don't export it
	// anymore. We should eventually try to remove it altogether.
	// TODO(gri) remove this
	var gcCompatibilityMode bool

	// TypeString returns the string representation of typ.
	// The Qualifier controls the printing of
	// package-level objects, and may be nil.
	func TypeString(typ Type, qf Qualifier) string {
	var buf bytes.Buffer
	WriteType(&buf, typ, qf)
	return buf.String()
	}

	// WriteType writes the string representation of typ to buf.
	// The Qualifier controls the printing of
	// package-level objects, and may be nil.
	func WriteType(buf *bytes.Buffer, typ Type, qf Qualifier) {
	writeType(buf, typ, qf, make([]Type, 0, 8))
	}

	// instanceMarker is the prefix for an instantiated type
	// in "non-evaluated" instance form.
	const instanceMarker = '#'

	func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
	// Theoretically, this is a quadratic lookup algorithm, but in
	// practice deeply nested composite types with unnamed component
	// types are uncommon. This code is likely more efficient than
	// using a map.
	for _, t := range visited {
	if t == typ {
	fmt.Fprintf(buf, "○%T", goTypeName(typ)) // cycle to typ
	return
	}
	}
	visited = append(visited, typ)

	switch t := typ.(type) {
	case nil:
	buf.WriteString("<nil>")

	case *Basic:
	// exported basic types go into package unsafe
	// (currently this is just unsafe.Pointer)
	if token.IsExported(t.name) {
	if obj, _ := Unsafe.scope.Lookup(t.name).(*TypeName); obj != nil {
	writeTypeName(buf, obj, qf)
	break
	}
	}

	if gcCompatibilityMode {
	// forget the alias names
	switch t.kind {
	case Byte:
	t = Typ[Uint8]
	case Rune:
	t = Typ[Int32]
	}
	}
	buf.WriteString(t.name)

	case *Array:
	fmt.Fprintf(buf, "[%d]", t.len)
	writeType(buf, t.elem, qf, visited)

	case *Slice:
	buf.WriteString("[]")
	writeType(buf, t.elem, qf, visited)

	case *Struct:
	buf.WriteString("struct{")
	for i, f := range t.fields {
	if i > 0 {
	buf.WriteString("; ")
	}
	// This doesn't do the right thing for embedded type
	// aliases where we should print the alias name, not
	// the aliased type (see issue #44410).
	if !f.embedded {
	buf.WriteString(f.name)
	buf.WriteByte(' ')
	}
	writeType(buf, f.typ, qf, visited)
	if tag := t.Tag(i); tag != "" {
	fmt.Fprintf(buf, " %q", tag)
	}
	}
	buf.WriteByte('}')

	case *Pointer:
	buf.WriteByte('*')
	writeType(buf, t.base, qf, visited)

	case *Tuple:
	writeTuple(buf, t, false, qf, visited)

	case *Signature:
	buf.WriteString("func")
	writeSignature(buf, t, qf, visited)

	case *_Sum:
	for i, t := range t.types {
	if i > 0 {
	buf.WriteString(", ")
	}
	writeType(buf, t, qf, visited)
	}

	case *Interface:
	// We write the source-level methods and embedded types rather
	// than the actual method set since resolved method signatures
	// may have non-printable cycles if parameters have embedded
	// interface types that (directly or indirectly) embed the
	// current interface. For instance, consider the result type
	// of m:
	//
	// type T interface{
	// m() interface{ T }
	// }
	//
	buf.WriteString("interface{")
	empty := true
	if gcCompatibilityMode {
	// print flattened interface
	// (useful to compare against gc-generated interfaces)
	for i, m := range t.allMethods {
	if i > 0 {
	buf.WriteString("; ")
	}
	buf.WriteString(m.name)
	writeSignature(buf, m.typ.(*Signature), qf, visited)
	empty = false
	}
	if !empty && t.allTypes != nil {
	buf.WriteString("; ")
	}
	if t.allTypes != nil {
	buf.WriteString("type ")
	writeType(buf, t.allTypes, qf, visited)
	}
	} else {
	// print explicit interface methods and embedded types
	for i, m := range t.methods {
	if i > 0 {
	buf.WriteString("; ")
	}
	buf.WriteString(m.name)
	writeSignature(buf, m.typ.(*Signature), qf, visited)
	empty = false
	}
	if !empty && t.types != nil {
	buf.WriteString("; ")
	}
	if t.types != nil {
	buf.WriteString("type ")
	writeType(buf, t.types, qf, visited)
	empty = false
	}
	if !empty && len(t.embeddeds) > 0 {
	buf.WriteString("; ")
	}
	for i, typ := range t.embeddeds {
	if i > 0 {
	buf.WriteString("; ")
	}
	writeType(buf, typ, qf, visited)
	empty = false
	}
	}
	if t.allMethods == nil \|\| len(t.methods) > len(t.allMethods) {
	if !empty {
	buf.WriteByte(' ')
	}
	buf.WriteString("/* incomplete */")
	}
	buf.WriteByte('}')

	case *Map:
	buf.WriteString("map[")
	writeType(buf, t.key, qf, visited)
	buf.WriteByte(']')
	writeType(buf, t.elem, qf, visited)

	case *Chan:
	var s string
	var parens bool
	switch t.dir {
	case SendRecv:
	s = "chan "
	// chan (<-chan T) requires parentheses
	if c, _ := t.elem.(*Chan); c != nil && c.dir == RecvOnly {
	parens = true
	}
	case SendOnly:
	s = "chan<- "
	case RecvOnly:
	s = "<-chan "
	default:
	panic("unreachable")
	}
	buf.WriteString(s)
	if parens {
	buf.WriteByte('(')
	}
	writeType(buf, t.elem, qf, visited)
	if parens {
	buf.WriteByte(')')
	}

	case *Named:
	writeTypeName(buf, t.obj, qf)
	if t.targs != nil {
	// instantiated type
	buf.WriteByte('[')
	writeTypeList(buf, t.targs, qf, visited)
	buf.WriteByte(']')
	} else if t.tparams != nil {
	// parameterized type
	writeTParamList(buf, t.tparams, qf, visited)
	}

	case *_TypeParam:
	s := "?"
	if t.obj != nil {
	s = t.obj.name
	}
	buf.WriteString(s + subscript(t.id))

	case *instance:
	buf.WriteByte(instanceMarker) // indicate "non-evaluated" syntactic instance
	writeTypeName(buf, t.base.obj, qf)
	buf.WriteByte('[')
	writeTypeList(buf, t.targs, qf, visited)
	buf.WriteByte(']')

	case *bottom:
	buf.WriteString("⊥")

	case *top:
	buf.WriteString("⊤")

	default:
	// For externally defined implementations of Type.
	buf.WriteString(t.String())
	}
	}

	func writeTypeList(buf *bytes.Buffer, list []Type, qf Qualifier, visited []Type) {
	for i, typ := range list {
	if i > 0 {
	buf.WriteString(", ")
	}
	writeType(buf, typ, qf, visited)
	}
	}

	func writeTParamList(buf bytes.Buffer, list []TypeName, qf Qualifier, visited []Type) {
	// TODO(rFindley) compare this with the corresponding implementation in types2
	buf.WriteString("[")
	var prev Type
	for i, p := range list {
	// TODO(rFindley) support 'any' sugar here.
	var b Type = &emptyInterface
	if t, _ := p.typ.(*_TypeParam); t != nil && t.bound != nil {
	b = t.bound
	}
	if i > 0 {
	if b != prev {
	// type bound changed - write previous one before advancing
	buf.WriteByte(' ')
	writeType(buf, prev, qf, visited)
	}
	buf.WriteString(", ")
	}
	prev = b

	if t, _ := p.typ.(*_TypeParam); t != nil {
	writeType(buf, t, qf, visited)
	} else {
	buf.WriteString(p.name)
	}
	}
	if prev != nil {
	buf.WriteByte(' ')
	writeType(buf, prev, qf, visited)
	}
	buf.WriteByte(']')
	}

	func writeTypeName(buf bytes.Buffer, obj TypeName, qf Qualifier) {
	s := "<Named w/o object>"
	if obj != nil {
	if obj.pkg != nil {
	writePackage(buf, obj.pkg, qf)
	}
	// TODO(gri): function-local named types should be displayed
	// differently from named types at package level to avoid
	// ambiguity.
	s = obj.name
	}
	buf.WriteString(s)
	}

	func writeTuple(buf bytes.Buffer, tup Tuple, variadic bool, qf Qualifier, visited []Type) {
	buf.WriteByte('(')
	if tup != nil {
	for i, v := range tup.vars {
	if i > 0 {
	buf.WriteString(", ")
	}
	if v.name != "" {
	buf.WriteString(v.name)
	buf.WriteByte(' ')
	}
	typ := v.typ
	if variadic && i == len(tup.vars)-1 {
	if s, ok := typ.(*Slice); ok {
	buf.WriteString("...")
	typ = s.elem
	} else {
	// special case:
	// append(s, "foo"...) leads to signature func([]byte, string...)
	if t := asBasic(typ); t == nil \|\| t.kind != String {
	panic("internal error: string type expected")
	}
	writeType(buf, typ, qf, visited)
	buf.WriteString("...")
	continue
	}
	}
	writeType(buf, typ, qf, visited)
	}
	}
	buf.WriteByte(')')
	}

	// WriteSignature writes the representation of the signature sig to buf,
	// without a leading "func" keyword.
	// The Qualifier controls the printing of
	// package-level objects, and may be nil.
	func WriteSignature(buf bytes.Buffer, sig Signature, qf Qualifier) {
	writeSignature(buf, sig, qf, make([]Type, 0, 8))
	}

	func writeSignature(buf bytes.Buffer, sig Signature, qf Qualifier, visited []Type) {
	if sig.tparams != nil {
	writeTParamList(buf, sig.tparams, qf, visited)
	}

	writeTuple(buf, sig.params, sig.variadic, qf, visited)

	n := sig.results.Len()
	if n == 0 {
	// no result
	return
	}

	buf.WriteByte(' ')
	if n == 1 && sig.results.vars[0].name == "" {
	// single unnamed result
	writeType(buf, sig.results.vars[0].typ, qf, visited)
	return
	}

	// multiple or named result(s)
	writeTuple(buf, sig.results, false, qf, visited)
	}

	// subscript returns the decimal (utf8) representation of x using subscript digits.
	func subscript(x uint64) string {
	const w = len("₀") // all digits 0...9 have the same utf8 width
	var buf [32 * w]byte
	i := len(buf)
	for {
	i -= w
	utf8.EncodeRune(buf[i:], '₀'+rune(x%10)) // '₀' == U+2080
	x /= 10
	if x == 0 {
	break
	}
	}
	return string(buf[i:])
	}