src/cmd/compile/internal/types/fmt.go - go - Git at Google

 // Copyright 2009 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 types

 import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
 	"strconv"
 	"sync"

 	"cmd/compile/internal/base"
 	"cmd/internal/notsha256"
 )

 // BuiltinPkg is a fake package that declares the universe block.
 var BuiltinPkg *Pkg

 // LocalPkg is the package being compiled.
 var LocalPkg *Pkg

 // UnsafePkg is package unsafe.
 var UnsafePkg *Pkg

 // BlankSym is the blank (_) symbol.
 var BlankSym *Sym

 // numImport tracks how often a package with a given name is imported.
 // It is used to provide a better error message (by using the package
 // path to disambiguate) if a package that appears multiple times with
 // the same name appears in an error message.
 var NumImport = make(map[string]int)

 // fmtMode represents the kind of printing being done.
 // The default is regular Go syntax (fmtGo).
 // fmtDebug is like fmtGo but for debugging dumps and prints the type kind too.
 // fmtTypeID and fmtTypeIDName are for generating various unique representations
 // of types used in hashes, the linker, and function/method instantiations.
 type fmtMode int

 const (
 	fmtGo fmtMode = iota
 	fmtDebug
 	fmtTypeID
 	fmtTypeIDName
 )

 // Sym

 // Format implements formatting for a Sym.
 // The valid formats are:
 //
 //	%v	Go syntax: Name for symbols in the local package, PkgName.Name for imported symbols.
 //	%+v	Debug syntax: always include PkgName. prefix even for local names.
 //	%S	Short syntax: Name only, no matter what.
 func (s *Sym) Format(f fmt.State, verb rune) {
 	mode := fmtGo
 	switch verb {
 	case 'v', 'S':
 		if verb == 'v' && f.Flag('+') {
 			mode = fmtDebug
 		}
 		fmt.Fprint(f, sconv(s, verb, mode))

 	default:
 		fmt.Fprintf(f, "%%!%c(*types.Sym=%p)", verb, s)
 	}
 }

 func (s *Sym) String() string {
 	return sconv(s, 0, fmtGo)
 }

 // See #16897 for details about performance implications
 // before changing the implementation of sconv.
 func sconv(s *Sym, verb rune, mode fmtMode) string {
 	if verb == 'L' {
 		panic("linksymfmt")
 	}

 	if s == nil {
 		return "<S>"
 	}

 	q := pkgqual(s.Pkg, verb, mode)
 	if q == "" {
 		return s.Name
 	}

 	buf := fmtBufferPool.Get().(*bytes.Buffer)
 	buf.Reset()
 	defer fmtBufferPool.Put(buf)

 	buf.WriteString(q)
 	buf.WriteByte('.')
 	buf.WriteString(s.Name)
 	return InternString(buf.Bytes())
 }

 func sconv2(b *bytes.Buffer, s *Sym, verb rune, mode fmtMode) {
 	if verb == 'L' {
 		panic("linksymfmt")
 	}
 	if s == nil {
 		b.WriteString("<S>")
 		return
 	}

 	symfmt(b, s, verb, mode)
 }

 func symfmt(b *bytes.Buffer, s *Sym, verb rune, mode fmtMode) {
 	name := s.Name
 	if q := pkgqual(s.Pkg, verb, mode); q != "" {
 		b.WriteString(q)
 		b.WriteByte('.')
 	}
 	b.WriteString(name)
 }

 // pkgqual returns the qualifier that should be used for printing
 // symbols from the given package in the given mode.
 // If it returns the empty string, no qualification is needed.
 func pkgqual(pkg *Pkg, verb rune, mode fmtMode) string {
 	if pkg == nil {
 		return ""
 	}
 	if verb != 'S' {
 		switch mode {
 		case fmtGo: // This is for the user
 			if pkg == BuiltinPkg || pkg == LocalPkg {
 				return ""
 			}

 			// If the name was used by multiple packages, display the full path,
 			if pkg.Name != "" && NumImport[pkg.Name] > 1 {
 				return strconv.Quote(pkg.Path)
 			}
 			return pkg.Name

 		case fmtDebug:
 			return pkg.Name

 		case fmtTypeIDName:
 			// dcommontype, typehash
 			return pkg.Name

 		case fmtTypeID:
 			// (methodsym), typesym, weaksym
 			return pkg.Prefix
 		}
 	}

 	return ""
 }

 // Type

 var BasicTypeNames = []string{
 	TINT:        "int",
 	TUINT:       "uint",
 	TINT8:       "int8",
 	TUINT8:      "uint8",
 	TINT16:      "int16",
 	TUINT16:     "uint16",
 	TINT32:      "int32",
 	TUINT32:     "uint32",
 	TINT64:      "int64",
 	TUINT64:     "uint64",
 	TUINTPTR:    "uintptr",
 	TFLOAT32:    "float32",
 	TFLOAT64:    "float64",
 	TCOMPLEX64:  "complex64",
 	TCOMPLEX128: "complex128",
 	TBOOL:       "bool",
 	TANY:        "any",
 	TSTRING:     "string",
 	TNIL:        "nil",
 	TIDEAL:      "untyped number",
 	TBLANK:      "blank",
 }

 var fmtBufferPool = sync.Pool{
 	New: func() interface{} {
 		return new(bytes.Buffer)
 	},
 }

 // Format implements formatting for a Type.
 // The valid formats are:
 //
 //	%v	Go syntax
 //	%+v	Debug syntax: Go syntax with a KIND- prefix for all but builtins.
 //	%L	Go syntax for underlying type if t is named
 //	%S	short Go syntax: drop leading "func" in function type
 //	%-S	special case for method receiver symbol
 func (t *Type) Format(s fmt.State, verb rune) {
 	mode := fmtGo
 	switch verb {
 	case 'v', 'S', 'L':
 		if verb == 'v' && s.Flag('+') { // %+v is debug format
 			mode = fmtDebug
 		}
 		if verb == 'S' && s.Flag('-') { // %-S is special case for receiver - short typeid format
 			mode = fmtTypeID
 		}
 		fmt.Fprint(s, tconv(t, verb, mode))
 	default:
 		fmt.Fprintf(s, "%%!%c(*Type=%p)", verb, t)
 	}
 }

 // String returns the Go syntax for the type t.
 func (t *Type) String() string {
 	return tconv(t, 0, fmtGo)
 }

 // LinkString returns a string description of t, suitable for use in
 // link symbols.
 //
 // The description corresponds to type identity. That is, for any pair
 // of types t1 and t2, Identical(t1, t2) == (t1.LinkString() ==
 // t2.LinkString()) is true. Thus it's safe to use as a map key to
 // implement a type-identity-keyed map.
 func (t *Type) LinkString() string {
 	return tconv(t, 0, fmtTypeID)
 }

 // NameString generates a user-readable, mostly unique string
 // description of t. NameString always returns the same description
 // for identical types, even across compilation units.
 //
 // NameString qualifies identifiers by package name, so it has
 // collisions when different packages share the same names and
 // identifiers. It also does not distinguish function-scope defined
 // types from package-scoped defined types or from each other.
 func (t *Type) NameString() string {
 	return tconv(t, 0, fmtTypeIDName)
 }

 func tconv(t *Type, verb rune, mode fmtMode) string {
 	buf := fmtBufferPool.Get().(*bytes.Buffer)
 	buf.Reset()
 	defer fmtBufferPool.Put(buf)

 	tconv2(buf, t, verb, mode, nil)
 	return InternString(buf.Bytes())
 }

 // tconv2 writes a string representation of t to b.
 // flag and mode control exactly what is printed.
 // Any types x that are already in the visited map get printed as @%d where %d=visited[x].
 // See #16897 before changing the implementation of tconv.
 func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type]int) {
 	if off, ok := visited[t]; ok {
 		// We've seen this type before, so we're trying to print it recursively.
 		// Print a reference to it instead.
 		fmt.Fprintf(b, "@%d", off)
 		return
 	}
 	if t == nil {
 		b.WriteString("<T>")
 		return
 	}
 	if t.Kind() == TSSA {
 		b.WriteString(t.extra.(string))
 		return
 	}
 	if t.Kind() == TTUPLE {
 		b.WriteString(t.FieldType(0).String())
 		b.WriteByte(',')
 		b.WriteString(t.FieldType(1).String())
 		return
 	}

 	if t.Kind() == TRESULTS {
 		tys := t.extra.(*Results).Types
 		for i, et := range tys {
 			if i > 0 {
 				b.WriteByte(',')
 			}
 			b.WriteString(et.String())
 		}
 		return
 	}

 	if t == AnyType || t == ByteType || t == RuneType {
 		// in %-T mode collapse predeclared aliases with their originals.
 		switch mode {
 		case fmtTypeIDName, fmtTypeID:
 			t = Types[t.Kind()]
 		default:
 			sconv2(b, t.Sym(), 'S', mode)
 			return
 		}
 	}
 	if t == ErrorType {
 		b.WriteString("error")
 		return
 	}

 	// Unless the 'L' flag was specified, if the type has a name, just print that name.
 	if verb != 'L' && t.Sym() != nil && t != Types[t.Kind()] {
 		// Default to 'v' if verb is invalid.
 		if verb != 'S' {
 			verb = 'v'
 		}

 		// In unified IR, function-scope defined types will have a ·N
 		// suffix embedded directly in their Name. Trim this off for
 		// non-fmtTypeID modes.
 		sym := t.Sym()
 		if mode != fmtTypeID {
 			base, _ := SplitVargenSuffix(sym.Name)
 			if len(base) < len(sym.Name) {
 				sym = &Sym{Pkg: sym.Pkg, Name: base}
 			}
 		}
 		sconv2(b, sym, verb, mode)
 		return
 	}

 	if int(t.Kind()) < len(BasicTypeNames) && BasicTypeNames[t.Kind()] != "" {
 		var name string
 		switch t {
 		case UntypedBool:
 			name = "untyped bool"
 		case UntypedString:
 			name = "untyped string"
 		case UntypedInt:
 			name = "untyped int"
 		case UntypedRune:
 			name = "untyped rune"
 		case UntypedFloat:
 			name = "untyped float"
 		case UntypedComplex:
 			name = "untyped complex"
 		default:
 			name = BasicTypeNames[t.Kind()]
 		}
 		b.WriteString(name)
 		return
 	}

 	if mode == fmtDebug {
 		b.WriteString(t.Kind().String())
 		b.WriteByte('-')
 		tconv2(b, t, 'v', fmtGo, visited)
 		return
 	}

 	// At this point, we might call tconv2 recursively. Add the current type to the visited list so we don't
 	// try to print it recursively.
 	// We record the offset in the result buffer where the type's text starts. This offset serves as a reference
 	// point for any later references to the same type.
 	// Note that we remove the type from the visited map as soon as the recursive call is done.
 	// This prevents encoding types like map[*int]*int as map[*int]@4. (That encoding would work,
 	// but I'd like to use the @ notation only when strictly necessary.)
 	if visited == nil {
 		visited = map[*Type]int{}
 	}
 	visited[t] = b.Len()
 	defer delete(visited, t)

 	switch t.Kind() {
 	case TPTR:
 		b.WriteByte('*')
 		switch mode {
 		case fmtTypeID, fmtTypeIDName:
 			if verb == 'S' {
 				tconv2(b, t.Elem(), 'S', mode, visited)
 				return
 			}
 		}
 		tconv2(b, t.Elem(), 'v', mode, visited)

 	case TARRAY:
 		b.WriteByte('[')
 		b.WriteString(strconv.FormatInt(t.NumElem(), 10))
 		b.WriteByte(']')
 		tconv2(b, t.Elem(), 0, mode, visited)

 	case TSLICE:
 		b.WriteString("[]")
 		tconv2(b, t.Elem(), 0, mode, visited)

 	case TCHAN:
 		switch t.ChanDir() {
 		case Crecv:
 			b.WriteString("<-chan ")
 			tconv2(b, t.Elem(), 0, mode, visited)
 		case Csend:
 			b.WriteString("chan<- ")
 			tconv2(b, t.Elem(), 0, mode, visited)
 		default:
 			b.WriteString("chan ")
 			if t.Elem() != nil && t.Elem().IsChan() && t.Elem().Sym() == nil && t.Elem().ChanDir() == Crecv {
 				b.WriteByte('(')
 				tconv2(b, t.Elem(), 0, mode, visited)
 				b.WriteByte(')')
 			} else {
 				tconv2(b, t.Elem(), 0, mode, visited)
 			}
 		}

 	case TMAP:
 		b.WriteString("map[")
 		tconv2(b, t.Key(), 0, mode, visited)
 		b.WriteByte(']')
 		tconv2(b, t.Elem(), 0, mode, visited)

 	case TINTER:
 		if t.IsEmptyInterface() {
 			b.WriteString("interface {}")
 			break
 		}
 		b.WriteString("interface {")
 		for i, f := range t.AllMethods() {
 			if i != 0 {
 				b.WriteByte(';')
 			}
 			b.WriteByte(' ')
 			switch {
 			case f.Sym == nil:
 				// Check first that a symbol is defined for this type.
 				// Wrong interface definitions may have types lacking a symbol.
 				break
 			case IsExported(f.Sym.Name):
 				sconv2(b, f.Sym, 'S', mode)
 			default:
 				if mode != fmtTypeIDName {
 					mode = fmtTypeID
 				}
 				sconv2(b, f.Sym, 'v', mode)
 			}
 			tconv2(b, f.Type, 'S', mode, visited)
 		}
 		if len(t.AllMethods()) != 0 {
 			b.WriteByte(' ')
 		}
 		b.WriteByte('}')

 	case TFUNC:
 		if verb == 'S' {
 			// no leading func
 		} else {
 			if t.Recv() != nil {
 				b.WriteString("method")
 				formatParams(b, t.Recvs(), mode, visited)
 				b.WriteByte(' ')
 			}
 			b.WriteString("func")
 		}
 		formatParams(b, t.Params(), mode, visited)

 		switch t.NumResults() {
 		case 0:
 			// nothing to do

 		case 1:
 			b.WriteByte(' ')
 			tconv2(b, t.Result(0).Type, 0, mode, visited) // struct->field->field's type

 		default:
 			b.WriteByte(' ')
 			formatParams(b, t.Results(), mode, visited)
 		}

 	case TSTRUCT:
 		if m := t.StructType().Map; m != nil {
 			mt := m.MapType()
 			// Format the bucket struct for map[x]y as map.bucket[x]y.
 			// This avoids a recursive print that generates very long names.
 			switch t {
 			case mt.Bucket:
 				b.WriteString("map.bucket[")
 			default:
 				base.Fatalf("unknown internal map type")
 			}
 			tconv2(b, m.Key(), 0, mode, visited)
 			b.WriteByte(']')
 			tconv2(b, m.Elem(), 0, mode, visited)
 			break
 		}

 		b.WriteString("struct {")
 		for i, f := range t.Fields() {
 			if i != 0 {
 				b.WriteByte(';')
 			}
 			b.WriteByte(' ')
 			fldconv(b, f, 'L', mode, visited, false)
 		}
 		if t.NumFields() != 0 {
 			b.WriteByte(' ')
 		}
 		b.WriteByte('}')

 	case TFORW:
 		b.WriteString("undefined")
 		if t.Sym() != nil {
 			b.WriteByte(' ')
 			sconv2(b, t.Sym(), 'v', mode)
 		}

 	case TUNSAFEPTR:
 		b.WriteString("unsafe.Pointer")

 	case Txxx:
 		b.WriteString("Txxx")

 	default:
 		// Don't know how to handle - fall back to detailed prints
 		b.WriteString(t.Kind().String())
 		b.WriteString(" <")
 		sconv2(b, t.Sym(), 'v', mode)
 		b.WriteString(">")

 	}
 }

 func formatParams(b *bytes.Buffer, params []*Field, mode fmtMode, visited map[*Type]int) {
 	b.WriteByte('(')
 	fieldVerb := 'v'
 	switch mode {
 	case fmtTypeID, fmtTypeIDName, fmtGo:
 		// no argument names on function signature, and no "noescape"/"nosplit" tags
 		fieldVerb = 'S'
 	}
 	for i, param := range params {
 		if i != 0 {
 			b.WriteString(", ")
 		}
 		fldconv(b, param, fieldVerb, mode, visited, true)
 	}
 	b.WriteByte(')')
 }

 func fldconv(b *bytes.Buffer, f *Field, verb rune, mode fmtMode, visited map[*Type]int, isParam bool) {
 	if f == nil {
 		b.WriteString("<T>")
 		return
 	}

 	var name string
 	nameSep := " "
 	if verb != 'S' {
 		s := f.Sym

 		// Using type aliases and embedded fields, it's possible to
 		// construct types that can't be directly represented as a
 		// type literal. For example, given "type Int = int" (#50190),
 		// it would be incorrect to format "struct{ Int }" as either
 		// "struct{ int }" or "struct{ Int int }", because those each
 		// represent other, distinct types.
 		//
 		// So for the purpose of LinkString (i.e., fmtTypeID), we use
 		// the non-standard syntax "struct{ Int = int }" to represent
 		// embedded fields that have been renamed through the use of
 		// type aliases.
 		if f.Embedded != 0 {
 			if mode == fmtTypeID {
 				nameSep = " = "

 				// Compute tsym, the symbol that would normally be used as
 				// the field name when embedding f.Type.
 				// TODO(mdempsky): Check for other occurrences of this logic
 				// and deduplicate.
 				typ := f.Type
 				if typ.IsPtr() {
 					base.Assertf(typ.Sym() == nil, "embedded pointer type has name: %L", typ)
 					typ = typ.Elem()
 				}
 				tsym := typ.Sym()

 				// If the field name matches the embedded type's name, then
 				// suppress printing of the field name. For example, format
 				// "struct{ T }" as simply that instead of "struct{ T = T }".
 				if tsym != nil && (s == tsym || IsExported(tsym.Name) && s.Name == tsym.Name) {
 					s = nil
 				}
 			} else {
 				// Suppress the field name for embedded fields for
 				// non-LinkString formats, to match historical behavior.
 				// TODO(mdempsky): Re-evaluate this.
 				s = nil
 			}
 		}

 		if s != nil {
 			if isParam {
 				name = fmt.Sprint(f.Nname)
 			} else if verb == 'L' {
 				name = s.Name
 				if !IsExported(name) && mode != fmtTypeIDName {
 					name = sconv(s, 0, mode) // qualify non-exported names (used on structs, not on funarg)
 				}
 			} else {
 				name = sconv(s, 0, mode)
 			}
 		}
 	}

 	if name != "" {
 		b.WriteString(name)
 		b.WriteString(nameSep)
 	}

 	if f.IsDDD() {
 		var et *Type
 		if f.Type != nil {
 			et = f.Type.Elem()
 		}
 		b.WriteString("...")
 		tconv2(b, et, 0, mode, visited)
 	} else {
 		tconv2(b, f.Type, 0, mode, visited)
 	}

 	if verb != 'S' && !isParam && f.Note != "" {
 		b.WriteString(" ")
 		b.WriteString(strconv.Quote(f.Note))
 	}
 }

 // SplitVargenSuffix returns name split into a base string and a ·N
 // suffix, if any.
 func SplitVargenSuffix(name string) (base, suffix string) {
 	i := len(name)
 	for i > 0 && name[i-1] >= '0' && name[i-1] <= '9' {
 		i--
 	}
 	const dot = "·"
 	if i >= len(dot) && name[i-len(dot):i] == dot {
 		i -= len(dot)
 		return name[:i], name[i:]
 	}
 	return name, ""
 }

 // TypeHash computes a hash value for type t to use in type switch statements.
 func TypeHash(t *Type) uint32 {
 	p := t.LinkString()

 	// Using SHA256 is overkill, but reduces accidental collisions.
 	h := notsha256.Sum256([]byte(p))
 	return binary.LittleEndian.Uint32(h[:4])
 }
	// Copyright 2009 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 types

	import (
	"bytes"
	"encoding/binary"
	"fmt"
	"strconv"
	"sync"

	"cmd/compile/internal/base"
	"cmd/internal/notsha256"
	)

	// BuiltinPkg is a fake package that declares the universe block.
	var BuiltinPkg *Pkg

	// LocalPkg is the package being compiled.
	var LocalPkg *Pkg

	// UnsafePkg is package unsafe.
	var UnsafePkg *Pkg

	// BlankSym is the blank (_) symbol.
	var BlankSym *Sym

	// numImport tracks how often a package with a given name is imported.
	// It is used to provide a better error message (by using the package
	// path to disambiguate) if a package that appears multiple times with
	// the same name appears in an error message.
	var NumImport = make(map[string]int)

	// fmtMode represents the kind of printing being done.
	// The default is regular Go syntax (fmtGo).
	// fmtDebug is like fmtGo but for debugging dumps and prints the type kind too.
	// fmtTypeID and fmtTypeIDName are for generating various unique representations
	// of types used in hashes, the linker, and function/method instantiations.
	type fmtMode int

	const (
	fmtGo fmtMode = iota
	fmtDebug
	fmtTypeID
	fmtTypeIDName
	)

	// Sym

	// Format implements formatting for a Sym.
	// The valid formats are:
	//
	// %v Go syntax: Name for symbols in the local package, PkgName.Name for imported symbols.
	// %+v Debug syntax: always include PkgName. prefix even for local names.
	// %S Short syntax: Name only, no matter what.
	func (s *Sym) Format(f fmt.State, verb rune) {
	mode := fmtGo
	switch verb {
	case 'v', 'S':
	if verb == 'v' && f.Flag('+') {
	mode = fmtDebug
	}
	fmt.Fprint(f, sconv(s, verb, mode))

	default:
	fmt.Fprintf(f, "%%!%c(*types.Sym=%p)", verb, s)
	}
	}

	func (s *Sym) String() string {
	return sconv(s, 0, fmtGo)
	}

	// See #16897 for details about performance implications
	// before changing the implementation of sconv.
	func sconv(s *Sym, verb rune, mode fmtMode) string {
	if verb == 'L' {
	panic("linksymfmt")
	}

	if s == nil {
	return "<S>"
	}

	q := pkgqual(s.Pkg, verb, mode)
	if q == "" {
	return s.Name
	}

	buf := fmtBufferPool.Get().(*bytes.Buffer)
	buf.Reset()
	defer fmtBufferPool.Put(buf)

	buf.WriteString(q)
	buf.WriteByte('.')
	buf.WriteString(s.Name)
	return InternString(buf.Bytes())
	}

	func sconv2(b bytes.Buffer, s Sym, verb rune, mode fmtMode) {
	if verb == 'L' {
	panic("linksymfmt")
	}
	if s == nil {
	b.WriteString("<S>")
	return
	}

	symfmt(b, s, verb, mode)
	}

	func symfmt(b bytes.Buffer, s Sym, verb rune, mode fmtMode) {
	name := s.Name
	if q := pkgqual(s.Pkg, verb, mode); q != "" {
	b.WriteString(q)
	b.WriteByte('.')
	}
	b.WriteString(name)
	}

	// pkgqual returns the qualifier that should be used for printing
	// symbols from the given package in the given mode.
	// If it returns the empty string, no qualification is needed.
	func pkgqual(pkg *Pkg, verb rune, mode fmtMode) string {
	if pkg == nil {
	return ""
	}
	if verb != 'S' {
	switch mode {
	case fmtGo: // This is for the user
	if pkg == BuiltinPkg \|\| pkg == LocalPkg {
	return ""
	}

	// If the name was used by multiple packages, display the full path,
	if pkg.Name != "" && NumImport[pkg.Name] > 1 {
	return strconv.Quote(pkg.Path)
	}
	return pkg.Name

	case fmtDebug:
	return pkg.Name

	case fmtTypeIDName:
	// dcommontype, typehash
	return pkg.Name

	case fmtTypeID:
	// (methodsym), typesym, weaksym
	return pkg.Prefix
	}
	}

	return ""
	}

	// Type

	var BasicTypeNames = []string{
	TINT: "int",
	TUINT: "uint",
	TINT8: "int8",
	TUINT8: "uint8",
	TINT16: "int16",
	TUINT16: "uint16",
	TINT32: "int32",
	TUINT32: "uint32",
	TINT64: "int64",
	TUINT64: "uint64",
	TUINTPTR: "uintptr",
	TFLOAT32: "float32",
	TFLOAT64: "float64",
	TCOMPLEX64: "complex64",
	TCOMPLEX128: "complex128",
	TBOOL: "bool",
	TANY: "any",
	TSTRING: "string",
	TNIL: "nil",
	TIDEAL: "untyped number",
	TBLANK: "blank",
	}

	var fmtBufferPool = sync.Pool{
	New: func() interface{} {
	return new(bytes.Buffer)
	},
	}

	// Format implements formatting for a Type.
	// The valid formats are:
	//
	// %v Go syntax
	// %+v Debug syntax: Go syntax with a KIND- prefix for all but builtins.
	// %L Go syntax for underlying type if t is named
	// %S short Go syntax: drop leading "func" in function type
	// %-S special case for method receiver symbol
	func (t *Type) Format(s fmt.State, verb rune) {
	mode := fmtGo
	switch verb {
	case 'v', 'S', 'L':
	if verb == 'v' && s.Flag('+') { // %+v is debug format
	mode = fmtDebug
	}
	if verb == 'S' && s.Flag('-') { // %-S is special case for receiver - short typeid format
	mode = fmtTypeID
	}
	fmt.Fprint(s, tconv(t, verb, mode))
	default:
	fmt.Fprintf(s, "%%!%c(*Type=%p)", verb, t)
	}
	}

	// String returns the Go syntax for the type t.
	func (t *Type) String() string {
	return tconv(t, 0, fmtGo)
	}

	// LinkString returns a string description of t, suitable for use in
	// link symbols.
	//
	// The description corresponds to type identity. That is, for any pair
	// of types t1 and t2, Identical(t1, t2) == (t1.LinkString() ==
	// t2.LinkString()) is true. Thus it's safe to use as a map key to
	// implement a type-identity-keyed map.
	func (t *Type) LinkString() string {
	return tconv(t, 0, fmtTypeID)
	}

	// NameString generates a user-readable, mostly unique string
	// description of t. NameString always returns the same description
	// for identical types, even across compilation units.
	//
	// NameString qualifies identifiers by package name, so it has
	// collisions when different packages share the same names and
	// identifiers. It also does not distinguish function-scope defined
	// types from package-scoped defined types or from each other.
	func (t *Type) NameString() string {
	return tconv(t, 0, fmtTypeIDName)
	}

	func tconv(t *Type, verb rune, mode fmtMode) string {
	buf := fmtBufferPool.Get().(*bytes.Buffer)
	buf.Reset()
	defer fmtBufferPool.Put(buf)

	tconv2(buf, t, verb, mode, nil)
	return InternString(buf.Bytes())
	}

	// tconv2 writes a string representation of t to b.
	// flag and mode control exactly what is printed.
	// Any types x that are already in the visited map get printed as @%d where %d=visited[x].
	// See #16897 before changing the implementation of tconv.
	func tconv2(b bytes.Buffer, t Type, verb rune, mode fmtMode, visited map[*Type]int) {
	if off, ok := visited[t]; ok {
	// We've seen this type before, so we're trying to print it recursively.
	// Print a reference to it instead.
	fmt.Fprintf(b, "@%d", off)
	return
	}
	if t == nil {
	b.WriteString("<T>")
	return
	}
	if t.Kind() == TSSA {
	b.WriteString(t.extra.(string))
	return
	}
	if t.Kind() == TTUPLE {
	b.WriteString(t.FieldType(0).String())
	b.WriteByte(',')
	b.WriteString(t.FieldType(1).String())
	return
	}

	if t.Kind() == TRESULTS {
	tys := t.extra.(*Results).Types
	for i, et := range tys {
	if i > 0 {
	b.WriteByte(',')
	}
	b.WriteString(et.String())
	}
	return
	}

	if t == AnyType \|\| t == ByteType \|\| t == RuneType {
	// in %-T mode collapse predeclared aliases with their originals.
	switch mode {
	case fmtTypeIDName, fmtTypeID:
	t = Types[t.Kind()]
	default:
	sconv2(b, t.Sym(), 'S', mode)
	return
	}
	}
	if t == ErrorType {
	b.WriteString("error")
	return
	}

	// Unless the 'L' flag was specified, if the type has a name, just print that name.
	if verb != 'L' && t.Sym() != nil && t != Types[t.Kind()] {
	// Default to 'v' if verb is invalid.
	if verb != 'S' {
	verb = 'v'
	}

	// In unified IR, function-scope defined types will have a ·N
	// suffix embedded directly in their Name. Trim this off for
	// non-fmtTypeID modes.
	sym := t.Sym()
	if mode != fmtTypeID {
	base, _ := SplitVargenSuffix(sym.Name)
	if len(base) < len(sym.Name) {
	sym = &Sym{Pkg: sym.Pkg, Name: base}
	}
	}
	sconv2(b, sym, verb, mode)
	return
	}

	if int(t.Kind()) < len(BasicTypeNames) && BasicTypeNames[t.Kind()] != "" {
	var name string
	switch t {
	case UntypedBool:
	name = "untyped bool"
	case UntypedString:
	name = "untyped string"
	case UntypedInt:
	name = "untyped int"
	case UntypedRune:
	name = "untyped rune"
	case UntypedFloat:
	name = "untyped float"
	case UntypedComplex:
	name = "untyped complex"
	default:
	name = BasicTypeNames[t.Kind()]
	}
	b.WriteString(name)
	return
	}

	if mode == fmtDebug {
	b.WriteString(t.Kind().String())
	b.WriteByte('-')
	tconv2(b, t, 'v', fmtGo, visited)
	return
	}

	// At this point, we might call tconv2 recursively. Add the current type to the visited list so we don't
	// try to print it recursively.
	// We record the offset in the result buffer where the type's text starts. This offset serves as a reference
	// point for any later references to the same type.
	// Note that we remove the type from the visited map as soon as the recursive call is done.
	// This prevents encoding types like map[int]int as map[*int]@4. (That encoding would work,
	// but I'd like to use the @ notation only when strictly necessary.)
	if visited == nil {
	visited = map[*Type]int{}
	}
	visited[t] = b.Len()
	defer delete(visited, t)

	switch t.Kind() {
	case TPTR:
	b.WriteByte('*')
	switch mode {
	case fmtTypeID, fmtTypeIDName:
	if verb == 'S' {
	tconv2(b, t.Elem(), 'S', mode, visited)
	return
	}
	}
	tconv2(b, t.Elem(), 'v', mode, visited)

	case TARRAY:
	b.WriteByte('[')
	b.WriteString(strconv.FormatInt(t.NumElem(), 10))
	b.WriteByte(']')
	tconv2(b, t.Elem(), 0, mode, visited)

	case TSLICE:
	b.WriteString("[]")
	tconv2(b, t.Elem(), 0, mode, visited)

	case TCHAN:
	switch t.ChanDir() {
	case Crecv:
	b.WriteString("<-chan ")
	tconv2(b, t.Elem(), 0, mode, visited)
	case Csend:
	b.WriteString("chan<- ")
	tconv2(b, t.Elem(), 0, mode, visited)
	default:
	b.WriteString("chan ")
	if t.Elem() != nil && t.Elem().IsChan() && t.Elem().Sym() == nil && t.Elem().ChanDir() == Crecv {
	b.WriteByte('(')
	tconv2(b, t.Elem(), 0, mode, visited)
	b.WriteByte(')')
	} else {
	tconv2(b, t.Elem(), 0, mode, visited)
	}
	}

	case TMAP:
	b.WriteString("map[")
	tconv2(b, t.Key(), 0, mode, visited)
	b.WriteByte(']')
	tconv2(b, t.Elem(), 0, mode, visited)

	case TINTER:
	if t.IsEmptyInterface() {
	b.WriteString("interface {}")
	break
	}
	b.WriteString("interface {")
	for i, f := range t.AllMethods() {
	if i != 0 {
	b.WriteByte(';')
	}
	b.WriteByte(' ')
	switch {
	case f.Sym == nil:
	// Check first that a symbol is defined for this type.
	// Wrong interface definitions may have types lacking a symbol.
	break
	case IsExported(f.Sym.Name):
	sconv2(b, f.Sym, 'S', mode)
	default:
	if mode != fmtTypeIDName {
	mode = fmtTypeID
	}
	sconv2(b, f.Sym, 'v', mode)
	}
	tconv2(b, f.Type, 'S', mode, visited)
	}
	if len(t.AllMethods()) != 0 {
	b.WriteByte(' ')
	}
	b.WriteByte('}')

	case TFUNC:
	if verb == 'S' {
	// no leading func
	} else {
	if t.Recv() != nil {
	b.WriteString("method")
	formatParams(b, t.Recvs(), mode, visited)
	b.WriteByte(' ')
	}
	b.WriteString("func")
	}
	formatParams(b, t.Params(), mode, visited)

	switch t.NumResults() {
	case 0:
	// nothing to do

	case 1:
	b.WriteByte(' ')
	tconv2(b, t.Result(0).Type, 0, mode, visited) // struct->field->field's type

	default:
	b.WriteByte(' ')
	formatParams(b, t.Results(), mode, visited)
	}

	case TSTRUCT:
	if m := t.StructType().Map; m != nil {
	mt := m.MapType()
	// Format the bucket struct for map[x]y as map.bucket[x]y.
	// This avoids a recursive print that generates very long names.
	switch t {
	case mt.Bucket:
	b.WriteString("map.bucket[")
	default:
	base.Fatalf("unknown internal map type")
	}
	tconv2(b, m.Key(), 0, mode, visited)
	b.WriteByte(']')
	tconv2(b, m.Elem(), 0, mode, visited)
	break
	}

	b.WriteString("struct {")
	for i, f := range t.Fields() {
	if i != 0 {
	b.WriteByte(';')
	}
	b.WriteByte(' ')
	fldconv(b, f, 'L', mode, visited, false)
	}
	if t.NumFields() != 0 {
	b.WriteByte(' ')
	}
	b.WriteByte('}')

	case TFORW:
	b.WriteString("undefined")
	if t.Sym() != nil {
	b.WriteByte(' ')
	sconv2(b, t.Sym(), 'v', mode)
	}

	case TUNSAFEPTR:
	b.WriteString("unsafe.Pointer")

	case Txxx:
	b.WriteString("Txxx")

	default:
	// Don't know how to handle - fall back to detailed prints
	b.WriteString(t.Kind().String())
	b.WriteString(" <")
	sconv2(b, t.Sym(), 'v', mode)
	b.WriteString(">")

	}
	}

	func formatParams(b bytes.Buffer, params []Field, mode fmtMode, visited map[*Type]int) {
	b.WriteByte('(')
	fieldVerb := 'v'
	switch mode {
	case fmtTypeID, fmtTypeIDName, fmtGo:
	// no argument names on function signature, and no "noescape"/"nosplit" tags
	fieldVerb = 'S'
	}
	for i, param := range params {
	if i != 0 {
	b.WriteString(", ")
	}
	fldconv(b, param, fieldVerb, mode, visited, true)
	}
	b.WriteByte(')')
	}

	func fldconv(b bytes.Buffer, f Field, verb rune, mode fmtMode, visited map[*Type]int, isParam bool) {
	if f == nil {
	b.WriteString("<T>")
	return
	}

	var name string
	nameSep := " "
	if verb != 'S' {
	s := f.Sym

	// Using type aliases and embedded fields, it's possible to
	// construct types that can't be directly represented as a
	// type literal. For example, given "type Int = int" (#50190),
	// it would be incorrect to format "struct{ Int }" as either
	// "struct{ int }" or "struct{ Int int }", because those each
	// represent other, distinct types.
	//
	// So for the purpose of LinkString (i.e., fmtTypeID), we use
	// the non-standard syntax "struct{ Int = int }" to represent
	// embedded fields that have been renamed through the use of
	// type aliases.
	if f.Embedded != 0 {
	if mode == fmtTypeID {
	nameSep = " = "

	// Compute tsym, the symbol that would normally be used as
	// the field name when embedding f.Type.
	// TODO(mdempsky): Check for other occurrences of this logic
	// and deduplicate.
	typ := f.Type
	if typ.IsPtr() {
	base.Assertf(typ.Sym() == nil, "embedded pointer type has name: %L", typ)
	typ = typ.Elem()
	}
	tsym := typ.Sym()

	// If the field name matches the embedded type's name, then
	// suppress printing of the field name. For example, format
	// "struct{ T }" as simply that instead of "struct{ T = T }".
	if tsym != nil && (s == tsym \|\| IsExported(tsym.Name) && s.Name == tsym.Name) {
	s = nil
	}
	} else {
	// Suppress the field name for embedded fields for
	// non-LinkString formats, to match historical behavior.
	// TODO(mdempsky): Re-evaluate this.
	s = nil
	}
	}

	if s != nil {
	if isParam {
	name = fmt.Sprint(f.Nname)
	} else if verb == 'L' {
	name = s.Name
	if !IsExported(name) && mode != fmtTypeIDName {
	name = sconv(s, 0, mode) // qualify non-exported names (used on structs, not on funarg)
	}
	} else {
	name = sconv(s, 0, mode)
	}
	}
	}

	if name != "" {
	b.WriteString(name)
	b.WriteString(nameSep)
	}

	if f.IsDDD() {
	var et *Type
	if f.Type != nil {
	et = f.Type.Elem()
	}
	b.WriteString("...")
	tconv2(b, et, 0, mode, visited)
	} else {
	tconv2(b, f.Type, 0, mode, visited)
	}

	if verb != 'S' && !isParam && f.Note != "" {
	b.WriteString(" ")
	b.WriteString(strconv.Quote(f.Note))
	}
	}

	// SplitVargenSuffix returns name split into a base string and a ·N
	// suffix, if any.
	func SplitVargenSuffix(name string) (base, suffix string) {
	i := len(name)
	for i > 0 && name[i-1] >= '0' && name[i-1] <= '9' {
	i--
	}
	const dot = "·"
	if i >= len(dot) && name[i-len(dot):i] == dot {
	i -= len(dot)
	return name[:i], name[i:]
	}
	return name, ""
	}

	// TypeHash computes a hash value for type t to use in type switch statements.
	func TypeHash(t *Type) uint32 {
	p := t.LinkString()

	// Using SHA256 is overkill, but reduces accidental collisions.
	h := notsha256.Sum256([]byte(p))
	return binary.LittleEndian.Uint32(h[:4])
	}