cmd/compile/internal/inline: score call sites exposed by inlines

[gostls13.git] / src / reflect / type.go

// 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 reflect implements run-time reflection, allowing a program to
// manipulate objects with arbitrary types. The typical use is to take a value
// with static type interface{} and extract its dynamic type information by
// calling TypeOf, which returns a Type.
//
// A call to ValueOf returns a Value representing the run-time data.
// Zero takes a Type and returns a Value representing a zero value
// for that type.
//
// See "The Laws of Reflection" for an introduction to reflection in Go:
// https://golang.org/doc/articles/laws_of_reflection.html
package reflect

import (
        "internal/abi"
        "internal/goarch"
        "strconv"
        "sync"
        "unicode"
        "unicode/utf8"
        "unsafe"
)

// Type is the representation of a Go type.
//
// Not all methods apply to all kinds of types. Restrictions,
// if any, are noted in the documentation for each method.
// Use the Kind method to find out the kind of type before
// calling kind-specific methods. Calling a method
// inappropriate to the kind of type causes a run-time panic.
//
// Type values are comparable, such as with the == operator,
// so they can be used as map keys.
// Two Type values are equal if they represent identical types.
type Type interface {
        // Methods applicable to all types.

        // Align returns the alignment in bytes of a value of
        // this type when allocated in memory.
        Align() int

        // FieldAlign returns the alignment in bytes of a value of
        // this type when used as a field in a struct.
        FieldAlign() int

        // Method returns the i'th method in the type's method set.
        // It panics if i is not in the range [0, NumMethod()).
        //
        // For a non-interface type T or *T, the returned Method's Type and Func
        // fields describe a function whose first argument is the receiver,
        // and only exported methods are accessible.
        //
        // For an interface type, the returned Method's Type field gives the
        // method signature, without a receiver, and the Func field is nil.
        //
        // Methods are sorted in lexicographic order.
        Method(int) Method

        // MethodByName returns the method with that name in the type's
        // method set and a boolean indicating if the method was found.
        //
        // For a non-interface type T or *T, the returned Method's Type and Func
        // fields describe a function whose first argument is the receiver.
        //
        // For an interface type, the returned Method's Type field gives the
        // method signature, without a receiver, and the Func field is nil.
        MethodByName(string) (Method, bool)

        // NumMethod returns the number of methods accessible using Method.
        //
        // For a non-interface type, it returns the number of exported methods.
        //
        // For an interface type, it returns the number of exported and unexported methods.
        NumMethod() int

        // Name returns the type's name within its package for a defined type.
        // For other (non-defined) types it returns the empty string.
        Name() string

        // PkgPath returns a defined type's package path, that is, the import path
        // that uniquely identifies the package, such as "encoding/base64".
        // If the type was predeclared (string, error) or not defined (*T, struct{},
        // []int, or A where A is an alias for a non-defined type), the package path
        // will be the empty string.
        PkgPath() string

        // Size returns the number of bytes needed to store
        // a value of the given type; it is analogous to unsafe.Sizeof.
        Size() uintptr

        // String returns a string representation of the type.
        // The string representation may use shortened package names
        // (e.g., base64 instead of "encoding/base64") and is not
        // guaranteed to be unique among types. To test for type identity,
        // compare the Types directly.
        String() string

        // Kind returns the specific kind of this type.
        Kind() Kind

        // Implements reports whether the type implements the interface type u.
        Implements(u Type) bool

        // AssignableTo reports whether a value of the type is assignable to type u.
        AssignableTo(u Type) bool

        // ConvertibleTo reports whether a value of the type is convertible to type u.
        // Even if ConvertibleTo returns true, the conversion may still panic.
        // For example, a slice of type []T is convertible to *[N]T,
        // but the conversion will panic if its length is less than N.
        ConvertibleTo(u Type) bool

        // Comparable reports whether values of this type are comparable.
        // Even if Comparable returns true, the comparison may still panic.
        // For example, values of interface type are comparable,
        // but the comparison will panic if their dynamic type is not comparable.
        Comparable() bool

        // Methods applicable only to some types, depending on Kind.
        // The methods allowed for each kind are:
        //
        //      Int*, Uint*, Float*, Complex*: Bits
        //      Array: Elem, Len
        //      Chan: ChanDir, Elem
        //      Func: In, NumIn, Out, NumOut, IsVariadic.
        //      Map: Key, Elem
        //      Pointer: Elem
        //      Slice: Elem
        //      Struct: Field, FieldByIndex, FieldByName, FieldByNameFunc, NumField

        // Bits returns the size of the type in bits.
        // It panics if the type's Kind is not one of the
        // sized or unsized Int, Uint, Float, or Complex kinds.
        Bits() int

        // ChanDir returns a channel type's direction.
        // It panics if the type's Kind is not Chan.
        ChanDir() ChanDir

        // IsVariadic reports whether a function type's final input parameter
        // is a "..." parameter. If so, t.In(t.NumIn() - 1) returns the parameter's
        // implicit actual type []T.
        //
        // For concreteness, if t represents func(x int, y ... float64), then
        //
        //      t.NumIn() == 2
        //      t.In(0) is the reflect.Type for "int"
        //      t.In(1) is the reflect.Type for "[]float64"
        //      t.IsVariadic() == true
        //
        // IsVariadic panics if the type's Kind is not Func.
        IsVariadic() bool

        // Elem returns a type's element type.
        // It panics if the type's Kind is not Array, Chan, Map, Pointer, or Slice.
        Elem() Type

        // Field returns a struct type's i'th field.
        // It panics if the type's Kind is not Struct.
        // It panics if i is not in the range [0, NumField()).
        Field(i int) StructField

        // FieldByIndex returns the nested field corresponding
        // to the index sequence. It is equivalent to calling Field
        // successively for each index i.
        // It panics if the type's Kind is not Struct.
        FieldByIndex(index []int) StructField

        // FieldByName returns the struct field with the given name
        // and a boolean indicating if the field was found.
        // If the returned field is promoted from an embedded struct,
        // then Offset in the returned StructField is the offset in
        // the embedded struct.
        FieldByName(name string) (StructField, bool)

        // FieldByNameFunc returns the struct field with a name
        // that satisfies the match function and a boolean indicating if
        // the field was found.
        //
        // FieldByNameFunc considers the fields in the struct itself
        // and then the fields in any embedded structs, in breadth first order,
        // stopping at the shallowest nesting depth containing one or more
        // fields satisfying the match function. If multiple fields at that depth
        // satisfy the match function, they cancel each other
        // and FieldByNameFunc returns no match.
        // This behavior mirrors Go's handling of name lookup in
        // structs containing embedded fields.
        //
        // If the returned field is promoted from an embedded struct,
        // then Offset in the returned StructField is the offset in
        // the embedded struct.
        FieldByNameFunc(match func(string) bool) (StructField, bool)

        // In returns the type of a function type's i'th input parameter.
        // It panics if the type's Kind is not Func.
        // It panics if i is not in the range [0, NumIn()).
        In(i int) Type

        // Key returns a map type's key type.
        // It panics if the type's Kind is not Map.
        Key() Type

        // Len returns an array type's length.
        // It panics if the type's Kind is not Array.
        Len() int

        // NumField returns a struct type's field count.
        // It panics if the type's Kind is not Struct.
        NumField() int

        // NumIn returns a function type's input parameter count.
        // It panics if the type's Kind is not Func.
        NumIn() int

        // NumOut returns a function type's output parameter count.
        // It panics if the type's Kind is not Func.
        NumOut() int

        // Out returns the type of a function type's i'th output parameter.
        // It panics if the type's Kind is not Func.
        // It panics if i is not in the range [0, NumOut()).
        Out(i int) Type

        common() *abi.Type
        uncommon() *uncommonType
}

// BUG(rsc): FieldByName and related functions consider struct field names to be equal
// if the names are equal, even if they are unexported names originating
// in different packages. The practical effect of this is that the result of
// t.FieldByName("x") is not well defined if the struct type t contains
// multiple fields named x (embedded from different packages).
// FieldByName may return one of the fields named x or may report that there are none.
// See https://golang.org/issue/4876 for more details.

/*
 * These data structures are known to the compiler (../cmd/compile/internal/reflectdata/reflect.go).
 * A few are known to ../runtime/type.go to convey to debuggers.
 * They are also known to ../runtime/type.go.
 */

// A Kind represents the specific kind of type that a [Type] represents.
// The zero Kind is not a valid kind.
type Kind uint

const (
        Invalid Kind = iota
        Bool
        Int
        Int8
        Int16
        Int32
        Int64
        Uint
        Uint8
        Uint16
        Uint32
        Uint64
        Uintptr
        Float32
        Float64
        Complex64
        Complex128
        Array
        Chan
        Func
        Interface
        Map
        Pointer
        Slice
        String
        Struct
        UnsafePointer
)

// Ptr is the old name for the [Pointer] kind.
const Ptr = Pointer

// uncommonType is present only for defined types or types with methods
// (if T is a defined type, the uncommonTypes for T and *T have methods).
// Using a pointer to this struct reduces the overall size required
// to describe a non-defined type with no methods.
type uncommonType = abi.UncommonType

// Embed this type to get common/uncommon
type common struct {
        abi.Type
}

// rtype is the common implementation of most values.
// It is embedded in other struct types.
type rtype struct {
        t abi.Type
}

func (t *rtype) common() *abi.Type {
        return &t.t
}

func (t *rtype) uncommon() *abi.UncommonType {
        return t.t.Uncommon()
}

type aNameOff = abi.NameOff
type aTypeOff = abi.TypeOff
type aTextOff = abi.TextOff

// ChanDir represents a channel type's direction.
type ChanDir int

const (
        RecvDir ChanDir             = 1 << iota // <-chan
        SendDir                                 // chan<-
        BothDir = RecvDir | SendDir             // chan
)

// arrayType represents a fixed array type.
type arrayType = abi.ArrayType

// chanType represents a channel type.
type chanType = abi.ChanType

// funcType represents a function type.
//
// A *rtype for each in and out parameter is stored in an array that
// directly follows the funcType (and possibly its uncommonType). So
// a function type with one method, one input, and one output is:
//
//      struct {
//              funcType
//              uncommonType
//              [2]*rtype    // [0] is in, [1] is out
//      }
type funcType = abi.FuncType

// interfaceType represents an interface type.
type interfaceType struct {
        abi.InterfaceType // can embed directly because not a public type.
}

func (t *interfaceType) nameOff(off aNameOff) abi.Name {
        return toRType(&t.Type).nameOff(off)
}

func nameOffFor(t *abi.Type, off aNameOff) abi.Name {
        return toRType(t).nameOff(off)
}

func typeOffFor(t *abi.Type, off aTypeOff) *abi.Type {
        return toRType(t).typeOff(off)
}

func (t *interfaceType) typeOff(off aTypeOff) *abi.Type {
        return toRType(&t.Type).typeOff(off)
}

func (t *interfaceType) common() *abi.Type {
        return &t.Type
}

func (t *interfaceType) uncommon() *abi.UncommonType {
        return t.Uncommon()
}

// mapType represents a map type.
type mapType struct {
        abi.MapType
}

// ptrType represents a pointer type.
type ptrType struct {
        abi.PtrType
}

// sliceType represents a slice type.
type sliceType struct {
        abi.SliceType
}

// Struct field
type structField = abi.StructField

// structType represents a struct type.
type structType struct {
        abi.StructType
}

func pkgPath(n abi.Name) string {
        if n.Bytes == nil || *n.DataChecked(0, "name flag field")&(1<<2) == 0 {
                return ""
        }
        i, l := n.ReadVarint(1)
        off := 1 + i + l
        if n.HasTag() {
                i2, l2 := n.ReadVarint(off)
                off += i2 + l2
        }
        var nameOff int32
        // Note that this field may not be aligned in memory,
        // so we cannot use a direct int32 assignment here.
        copy((*[4]byte)(unsafe.Pointer(&nameOff))[:], (*[4]byte)(unsafe.Pointer(n.DataChecked(off, "name offset field")))[:])
        pkgPathName := abi.Name{Bytes: (*byte)(resolveTypeOff(unsafe.Pointer(n.Bytes), nameOff))}
        return pkgPathName.Name()
}

func newName(n, tag string, exported, embedded bool) abi.Name {
        return abi.NewName(n, tag, exported, embedded)
}

/*
 * The compiler knows the exact layout of all the data structures above.
 * The compiler does not know about the data structures and methods below.
 */

// Method represents a single method.
type Method struct {
        // Name is the method name.
        Name string

        // PkgPath is the package path that qualifies a lower case (unexported)
        // method name. It is empty for upper case (exported) method names.
        // The combination of PkgPath and Name uniquely identifies a method
        // in a method set.
        // See https://golang.org/ref/spec#Uniqueness_of_identifiers
        PkgPath string

        Type  Type  // method type
        Func  Value // func with receiver as first argument
        Index int   // index for Type.Method
}

// IsExported reports whether the method is exported.
func (m Method) IsExported() bool {
        return m.PkgPath == ""
}

const (
        kindDirectIface = 1 << 5
        kindGCProg      = 1 << 6 // Type.gc points to GC program
        kindMask        = (1 << 5) - 1
)

// String returns the name of k.
func (k Kind) String() string {
        if uint(k) < uint(len(kindNames)) {
                return kindNames[uint(k)]
        }
        return "kind" + strconv.Itoa(int(k))
}

var kindNames = []string{
        Invalid:       "invalid",
        Bool:          "bool",
        Int:           "int",
        Int8:          "int8",
        Int16:         "int16",
        Int32:         "int32",
        Int64:         "int64",
        Uint:          "uint",
        Uint8:         "uint8",
        Uint16:        "uint16",
        Uint32:        "uint32",
        Uint64:        "uint64",
        Uintptr:       "uintptr",
        Float32:       "float32",
        Float64:       "float64",
        Complex64:     "complex64",
        Complex128:    "complex128",
        Array:         "array",
        Chan:          "chan",
        Func:          "func",
        Interface:     "interface",
        Map:           "map",
        Pointer:       "ptr",
        Slice:         "slice",
        String:        "string",
        Struct:        "struct",
        UnsafePointer: "unsafe.Pointer",
}

// resolveNameOff resolves a name offset from a base pointer.
// The (*rtype).nameOff method is a convenience wrapper for this function.
// Implemented in the runtime package.
//
//go:noescape
func resolveNameOff(ptrInModule unsafe.Pointer, off int32) unsafe.Pointer

// resolveTypeOff resolves an *rtype offset from a base type.
// The (*rtype).typeOff method is a convenience wrapper for this function.
// Implemented in the runtime package.
//
//go:noescape
func resolveTypeOff(rtype unsafe.Pointer, off int32) unsafe.Pointer

// resolveTextOff resolves a function pointer offset from a base type.
// The (*rtype).textOff method is a convenience wrapper for this function.
// Implemented in the runtime package.
//
//go:noescape
func resolveTextOff(rtype unsafe.Pointer, off int32) unsafe.Pointer

// addReflectOff adds a pointer to the reflection lookup map in the runtime.
// It returns a new ID that can be used as a typeOff or textOff, and will
// be resolved correctly. Implemented in the runtime package.
//
//go:noescape
func addReflectOff(ptr unsafe.Pointer) int32

// resolveReflectName adds a name to the reflection lookup map in the runtime.
// It returns a new nameOff that can be used to refer to the pointer.
func resolveReflectName(n abi.Name) aNameOff {
        return aNameOff(addReflectOff(unsafe.Pointer(n.Bytes)))
}

// resolveReflectType adds a *rtype to the reflection lookup map in the runtime.
// It returns a new typeOff that can be used to refer to the pointer.
func resolveReflectType(t *abi.Type) aTypeOff {
        return aTypeOff(addReflectOff(unsafe.Pointer(t)))
}

// resolveReflectText adds a function pointer to the reflection lookup map in
// the runtime. It returns a new textOff that can be used to refer to the
// pointer.
func resolveReflectText(ptr unsafe.Pointer) aTextOff {
        return aTextOff(addReflectOff(ptr))
}

func (t *rtype) nameOff(off aNameOff) abi.Name {
        return abi.Name{Bytes: (*byte)(resolveNameOff(unsafe.Pointer(t), int32(off)))}
}

func (t *rtype) typeOff(off aTypeOff) *abi.Type {
        return (*abi.Type)(resolveTypeOff(unsafe.Pointer(t), int32(off)))
}

func (t *rtype) textOff(off aTextOff) unsafe.Pointer {
        return resolveTextOff(unsafe.Pointer(t), int32(off))
}

func textOffFor(t *abi.Type, off aTextOff) unsafe.Pointer {
        return toRType(t).textOff(off)
}

func (t *rtype) String() string {
        s := t.nameOff(t.t.Str).Name()
        if t.t.TFlag&abi.TFlagExtraStar != 0 {
                return s[1:]
        }
        return s
}

func (t *rtype) Size() uintptr { return t.t.Size() }

func (t *rtype) Bits() int {
        if t == nil {
                panic("reflect: Bits of nil Type")
        }
        k := t.Kind()
        if k < Int || k > Complex128 {
                panic("reflect: Bits of non-arithmetic Type " + t.String())
        }
        return int(t.t.Size_) * 8
}

func (t *rtype) Align() int { return t.t.Align() }

func (t *rtype) FieldAlign() int { return t.t.FieldAlign() }

func (t *rtype) Kind() Kind { return Kind(t.t.Kind()) }

func (t *rtype) exportedMethods() []abi.Method {
        ut := t.uncommon()
        if ut == nil {
                return nil
        }
        return ut.ExportedMethods()
}

func (t *rtype) NumMethod() int {
        if t.Kind() == Interface {
                tt := (*interfaceType)(unsafe.Pointer(t))
                return tt.NumMethod()
        }
        return len(t.exportedMethods())
}

func (t *rtype) Method(i int) (m Method) {
        if t.Kind() == Interface {
                tt := (*interfaceType)(unsafe.Pointer(t))
                return tt.Method(i)
        }
        methods := t.exportedMethods()
        if i < 0 || i >= len(methods) {
                panic("reflect: Method index out of range")
        }
        p := methods[i]
        pname := t.nameOff(p.Name)
        m.Name = pname.Name()
        fl := flag(Func)
        mtyp := t.typeOff(p.Mtyp)
        ft := (*funcType)(unsafe.Pointer(mtyp))
        in := make([]Type, 0, 1+ft.NumIn())
        in = append(in, t)
        for _, arg := range ft.InSlice() {
                in = append(in, toRType(arg))
        }
        out := make([]Type, 0, ft.NumOut())
        for _, ret := range ft.OutSlice() {
                out = append(out, toRType(ret))
        }
        mt := FuncOf(in, out, ft.IsVariadic())
        m.Type = mt
        tfn := t.textOff(p.Tfn)
        fn := unsafe.Pointer(&tfn)
        m.Func = Value{&mt.(*rtype).t, fn, fl}

        m.Index = i
        return m
}

func (t *rtype) MethodByName(name string) (m Method, ok bool) {
        if t.Kind() == Interface {
                tt := (*interfaceType)(unsafe.Pointer(t))
                return tt.MethodByName(name)
        }
        ut := t.uncommon()
        if ut == nil {
                return Method{}, false
        }

        methods := ut.ExportedMethods()

        // We are looking for the first index i where the string becomes >= s.
        // This is a copy of sort.Search, with f(h) replaced by (t.nameOff(methods[h].name).name() >= name).
        i, j := 0, len(methods)
        for i < j {
                h := int(uint(i+j) >> 1) // avoid overflow when computing h
                // i ≤ h < j
                if !(t.nameOff(methods[h].Name).Name() >= name) {
                        i = h + 1 // preserves f(i-1) == false
                } else {
                        j = h // preserves f(j) == true
                }
        }
        // i == j, f(i-1) == false, and f(j) (= f(i)) == true  =>  answer is i.
        if i < len(methods) && name == t.nameOff(methods[i].Name).Name() {
                return t.Method(i), true
        }

        return Method{}, false
}

func (t *rtype) PkgPath() string {
        if t.t.TFlag&abi.TFlagNamed == 0 {
                return ""
        }
        ut := t.uncommon()
        if ut == nil {
                return ""
        }
        return t.nameOff(ut.PkgPath).Name()
}

func pkgPathFor(t *abi.Type) string {
        return toRType(t).PkgPath()
}

func (t *rtype) Name() string {
        if !t.t.HasName() {
                return ""
        }
        s := t.String()
        i := len(s) - 1
        sqBrackets := 0
        for i >= 0 && (s[i] != '.' || sqBrackets != 0) {
                switch s[i] {
                case ']':
                        sqBrackets++
                case '[':
                        sqBrackets--
                }
                i--
        }
        return s[i+1:]
}

func nameFor(t *abi.Type) string {
        return toRType(t).Name()
}

func (t *rtype) ChanDir() ChanDir {
        if t.Kind() != Chan {
                panic("reflect: ChanDir of non-chan type " + t.String())
        }
        tt := (*abi.ChanType)(unsafe.Pointer(t))
        return ChanDir(tt.Dir)
}

func toRType(t *abi.Type) *rtype {
        return (*rtype)(unsafe.Pointer(t))
}

func elem(t *abi.Type) *abi.Type {
        et := t.Elem()
        if et != nil {
                return et
        }
        panic("reflect: Elem of invalid type " + stringFor(t))
}

func (t *rtype) Elem() Type {
        return toType(elem(t.common()))
}

func (t *rtype) Field(i int) StructField {
        if t.Kind() != Struct {
                panic("reflect: Field of non-struct type " + t.String())
        }
        tt := (*structType)(unsafe.Pointer(t))
        return tt.Field(i)
}

func (t *rtype) FieldByIndex(index []int) StructField {
        if t.Kind() != Struct {
                panic("reflect: FieldByIndex of non-struct type " + t.String())
        }
        tt := (*structType)(unsafe.Pointer(t))
        return tt.FieldByIndex(index)
}

func (t *rtype) FieldByName(name string) (StructField, bool) {
        if t.Kind() != Struct {
                panic("reflect: FieldByName of non-struct type " + t.String())
        }
        tt := (*structType)(unsafe.Pointer(t))
        return tt.FieldByName(name)
}

func (t *rtype) FieldByNameFunc(match func(string) bool) (StructField, bool) {
        if t.Kind() != Struct {
                panic("reflect: FieldByNameFunc of non-struct type " + t.String())
        }
        tt := (*structType)(unsafe.Pointer(t))
        return tt.FieldByNameFunc(match)
}

func (t *rtype) Key() Type {
        if t.Kind() != Map {
                panic("reflect: Key of non-map type " + t.String())
        }
        tt := (*mapType)(unsafe.Pointer(t))
        return toType(tt.Key)
}

func (t *rtype) Len() int {
        if t.Kind() != Array {
                panic("reflect: Len of non-array type " + t.String())
        }
        tt := (*arrayType)(unsafe.Pointer(t))
        return int(tt.Len)
}

func (t *rtype) NumField() int {
        if t.Kind() != Struct {
                panic("reflect: NumField of non-struct type " + t.String())
        }
        tt := (*structType)(unsafe.Pointer(t))
        return len(tt.Fields)
}

func (t *rtype) In(i int) Type {
        if t.Kind() != Func {
                panic("reflect: In of non-func type " + t.String())
        }
        tt := (*abi.FuncType)(unsafe.Pointer(t))
        return toType(tt.InSlice()[i])
}

func (t *rtype) NumIn() int {
        if t.Kind() != Func {
                panic("reflect: NumIn of non-func type " + t.String())
        }
        tt := (*abi.FuncType)(unsafe.Pointer(t))
        return tt.NumIn()
}

func (t *rtype) NumOut() int {
        if t.Kind() != Func {
                panic("reflect: NumOut of non-func type " + t.String())
        }
        tt := (*abi.FuncType)(unsafe.Pointer(t))
        return tt.NumOut()
}

func (t *rtype) Out(i int) Type {
        if t.Kind() != Func {
                panic("reflect: Out of non-func type " + t.String())
        }
        tt := (*abi.FuncType)(unsafe.Pointer(t))
        return toType(tt.OutSlice()[i])
}

func (t *rtype) IsVariadic() bool {
        if t.Kind() != Func {
                panic("reflect: IsVariadic of non-func type " + t.String())
        }
        tt := (*abi.FuncType)(unsafe.Pointer(t))
        return tt.IsVariadic()
}

// add returns p+x.
//
// The whySafe string is ignored, so that the function still inlines
// as efficiently as p+x, but all call sites should use the string to
// record why the addition is safe, which is to say why the addition
// does not cause x to advance to the very end of p's allocation
// and therefore point incorrectly at the next block in memory.
func add(p unsafe.Pointer, x uintptr, whySafe string) unsafe.Pointer {
        return unsafe.Pointer(uintptr(p) + x)
}

func (d ChanDir) String() string {
        switch d {
        case SendDir:
                return "chan<-"
        case RecvDir:
                return "<-chan"
        case BothDir:
                return "chan"
        }
        return "ChanDir" + strconv.Itoa(int(d))
}

// Method returns the i'th method in the type's method set.
func (t *interfaceType) Method(i int) (m Method) {
        if i < 0 || i >= len(t.Methods) {
                return
        }
        p := &t.Methods[i]
        pname := t.nameOff(p.Name)
        m.Name = pname.Name()
        if !pname.IsExported() {
                m.PkgPath = pkgPath(pname)
                if m.PkgPath == "" {
                        m.PkgPath = t.PkgPath.Name()
                }
        }
        m.Type = toType(t.typeOff(p.Typ))
        m.Index = i
        return
}

// NumMethod returns the number of interface methods in the type's method set.
func (t *interfaceType) NumMethod() int { return len(t.Methods) }

// MethodByName method with the given name in the type's method set.
func (t *interfaceType) MethodByName(name string) (m Method, ok bool) {
        if t == nil {
                return
        }
        var p *abi.Imethod
        for i := range t.Methods {
                p = &t.Methods[i]
                if t.nameOff(p.Name).Name() == name {
                        return t.Method(i), true
                }
        }
        return
}

// A StructField describes a single field in a struct.
type StructField struct {
        // Name is the field name.
        Name string

        // PkgPath is the package path that qualifies a lower case (unexported)
        // field name. It is empty for upper case (exported) field names.
        // See https://golang.org/ref/spec#Uniqueness_of_identifiers
        PkgPath string

        Type      Type      // field type
        Tag       StructTag // field tag string
        Offset    uintptr   // offset within struct, in bytes
        Index     []int     // index sequence for Type.FieldByIndex
        Anonymous bool      // is an embedded field
}

// IsExported reports whether the field is exported.
func (f StructField) IsExported() bool {
        return f.PkgPath == ""
}

// A StructTag is the tag string in a struct field.
//
// By convention, tag strings are a concatenation of
// optionally space-separated key:"value" pairs.
// Each key is a non-empty string consisting of non-control
// characters other than space (U+0020 ' '), quote (U+0022 '"'),
// and colon (U+003A ':').  Each value is quoted using U+0022 '"'
// characters and Go string literal syntax.
type StructTag string

// Get returns the value associated with key in the tag string.
// If there is no such key in the tag, Get returns the empty string.
// If the tag does not have the conventional format, the value
// returned by Get is unspecified. To determine whether a tag is
// explicitly set to the empty string, use Lookup.
func (tag StructTag) Get(key string) string {
        v, _ := tag.Lookup(key)
        return v
}

// Lookup returns the value associated with key in the tag string.
// If the key is present in the tag the value (which may be empty)
// is returned. Otherwise the returned value will be the empty string.
// The ok return value reports whether the value was explicitly set in
// the tag string. If the tag does not have the conventional format,
// the value returned by Lookup is unspecified.
func (tag StructTag) Lookup(key string) (value string, ok bool) {
        // When modifying this code, also update the validateStructTag code
        // in cmd/vet/structtag.go.

        for tag != "" {
                // Skip leading space.
                i := 0
                for i < len(tag) && tag[i] == ' ' {
                        i++
                }
                tag = tag[i:]
                if tag == "" {
                        break
                }

                // Scan to colon. A space, a quote or a control character is a syntax error.
                // Strictly speaking, control chars include the range [0x7f, 0x9f], not just
                // [0x00, 0x1f], but in practice, we ignore the multi-byte control characters
                // as it is simpler to inspect the tag's bytes than the tag's runes.
                i = 0
                for i < len(tag) && tag[i] > ' ' && tag[i] != ':' && tag[i] != '"' && tag[i] != 0x7f {
                        i++
                }
                if i == 0 || i+1 >= len(tag) || tag[i] != ':' || tag[i+1] != '"' {
                        break
                }
                name := string(tag[:i])
                tag = tag[i+1:]

                // Scan quoted string to find value.
                i = 1
                for i < len(tag) && tag[i] != '"' {
                        if tag[i] == '\\' {
                                i++
                        }
                        i++
                }
                if i >= len(tag) {
                        break
                }
                qvalue := string(tag[:i+1])
                tag = tag[i+1:]

                if key == name {
                        value, err := strconv.Unquote(qvalue)
                        if err != nil {
                                break
                        }
                        return value, true
                }
        }
        return "", false
}

// Field returns the i'th struct field.
func (t *structType) Field(i int) (f StructField) {
        if i < 0 || i >= len(t.Fields) {
                panic("reflect: Field index out of bounds")
        }
        p := &t.Fields[i]
        f.Type = toType(p.Typ)
        f.Name = p.Name.Name()
        f.Anonymous = p.Embedded()
        if !p.Name.IsExported() {
                f.PkgPath = t.PkgPath.Name()
        }
        if tag := p.Name.Tag(); tag != "" {
                f.Tag = StructTag(tag)
        }
        f.Offset = p.Offset

        // NOTE(rsc): This is the only allocation in the interface
        // presented by a reflect.Type. It would be nice to avoid,
        // at least in the common cases, but we need to make sure
        // that misbehaving clients of reflect cannot affect other
        // uses of reflect. One possibility is CL 5371098, but we
        // postponed that ugliness until there is a demonstrated
        // need for the performance. This is issue 2320.
        f.Index = []int{i}
        return
}

// TODO(gri): Should there be an error/bool indicator if the index
// is wrong for FieldByIndex?

// FieldByIndex returns the nested field corresponding to index.
func (t *structType) FieldByIndex(index []int) (f StructField) {
        f.Type = toType(&t.Type)
        for i, x := range index {
                if i > 0 {
                        ft := f.Type
                        if ft.Kind() == Pointer && ft.Elem().Kind() == Struct {
                                ft = ft.Elem()
                        }
                        f.Type = ft
                }
                f = f.Type.Field(x)
        }
        return
}

// A fieldScan represents an item on the fieldByNameFunc scan work list.
type fieldScan struct {
        typ   *structType
        index []int
}

// FieldByNameFunc returns the struct field with a name that satisfies the
// match function and a boolean to indicate if the field was found.
func (t *structType) FieldByNameFunc(match func(string) bool) (result StructField, ok bool) {
        // This uses the same condition that the Go language does: there must be a unique instance
        // of the match at a given depth level. If there are multiple instances of a match at the
        // same depth, they annihilate each other and inhibit any possible match at a lower level.
        // The algorithm is breadth first search, one depth level at a time.

        // The current and next slices are work queues:
        // current lists the fields to visit on this depth level,
        // and next lists the fields on the next lower level.
        current := []fieldScan{}
        next := []fieldScan{{typ: t}}

        // nextCount records the number of times an embedded type has been
        // encountered and considered for queueing in the 'next' slice.
        // We only queue the first one, but we increment the count on each.
        // If a struct type T can be reached more than once at a given depth level,
        // then it annihilates itself and need not be considered at all when we
        // process that next depth level.
        var nextCount map[*structType]int

        // visited records the structs that have been considered already.
        // Embedded pointer fields can create cycles in the graph of
        // reachable embedded types; visited avoids following those cycles.
        // It also avoids duplicated effort: if we didn't find the field in an
        // embedded type T at level 2, we won't find it in one at level 4 either.
        visited := map[*structType]bool{}

        for len(next) > 0 {
                current, next = next, current[:0]
                count := nextCount
                nextCount = nil

                // Process all the fields at this depth, now listed in 'current'.
                // The loop queues embedded fields found in 'next', for processing during the next
                // iteration. The multiplicity of the 'current' field counts is recorded
                // in 'count'; the multiplicity of the 'next' field counts is recorded in 'nextCount'.
                for _, scan := range current {
                        t := scan.typ
                        if visited[t] {
                                // We've looked through this type before, at a higher level.
                                // That higher level would shadow the lower level we're now at,
                                // so this one can't be useful to us. Ignore it.
                                continue
                        }
                        visited[t] = true
                        for i := range t.Fields {
                                f := &t.Fields[i]
                                // Find name and (for embedded field) type for field f.
                                fname := f.Name.Name()
                                var ntyp *abi.Type
                                if f.Embedded() {
                                        // Embedded field of type T or *T.
                                        ntyp = f.Typ
                                        if ntyp.Kind() == abi.Pointer {
                                                ntyp = ntyp.Elem()
                                        }
                                }

                                // Does it match?
                                if match(fname) {
                                        // Potential match
                                        if count[t] > 1 || ok {
                                                // Name appeared multiple times at this level: annihilate.
                                                return StructField{}, false
                                        }
                                        result = t.Field(i)
                                        result.Index = nil
                                        result.Index = append(result.Index, scan.index...)
                                        result.Index = append(result.Index, i)
                                        ok = true
                                        continue
                                }

                                // Queue embedded struct fields for processing with next level,
                                // but only if we haven't seen a match yet at this level and only
                                // if the embedded types haven't already been queued.
                                if ok || ntyp == nil || ntyp.Kind() != abi.Struct {
                                        continue
                                }
                                styp := (*structType)(unsafe.Pointer(ntyp))
                                if nextCount[styp] > 0 {
                                        nextCount[styp] = 2 // exact multiple doesn't matter
                                        continue
                                }
                                if nextCount == nil {
                                        nextCount = map[*structType]int{}
                                }
                                nextCount[styp] = 1
                                if count[t] > 1 {
                                        nextCount[styp] = 2 // exact multiple doesn't matter
                                }
                                var index []int
                                index = append(index, scan.index...)
                                index = append(index, i)
                                next = append(next, fieldScan{styp, index})
                        }
                }
                if ok {
                        break
                }
        }
        return
}

// FieldByName returns the struct field with the given name
// and a boolean to indicate if the field was found.
func (t *structType) FieldByName(name string) (f StructField, present bool) {
        // Quick check for top-level name, or struct without embedded fields.
        hasEmbeds := false
        if name != "" {
                for i := range t.Fields {
                        tf := &t.Fields[i]
                        if tf.Name.Name() == name {
                                return t.Field(i), true
                        }
                        if tf.Embedded() {
                                hasEmbeds = true
                        }
                }
        }
        if !hasEmbeds {
                return
        }
        return t.FieldByNameFunc(func(s string) bool { return s == name })
}

// TypeOf returns the reflection [Type] that represents the dynamic type of i.
// If i is a nil interface value, TypeOf returns nil.
func TypeOf(i any) Type {
        eface := *(*emptyInterface)(unsafe.Pointer(&i))
        // Noescape so this doesn't make i to escape. See the comment
        // at Value.typ for why this is safe.
        return toType((*abi.Type)(noescape(unsafe.Pointer(eface.typ))))
}

// rtypeOf directly extracts the *rtype of the provided value.
func rtypeOf(i any) *abi.Type {
        eface := *(*emptyInterface)(unsafe.Pointer(&i))
        return eface.typ
}

// ptrMap is the cache for PointerTo.
var ptrMap sync.Map // map[*rtype]*ptrType

// PtrTo returns the pointer type with element t.
// For example, if t represents type Foo, PtrTo(t) represents *Foo.
//
// PtrTo is the old spelling of [PointerTo].
// The two functions behave identically.
//
// Deprecated: Superseded by [PointerTo].
func PtrTo(t Type) Type { return PointerTo(t) }

// PointerTo returns the pointer type with element t.
// For example, if t represents type Foo, PointerTo(t) represents *Foo.
func PointerTo(t Type) Type {
        return toRType(t.(*rtype).ptrTo())
}

func (t *rtype) ptrTo() *abi.Type {
        at := &t.t
        if at.PtrToThis != 0 {
                return t.typeOff(at.PtrToThis)
        }

        // Check the cache.
        if pi, ok := ptrMap.Load(t); ok {
                return &pi.(*ptrType).Type
        }

        // Look in known types.
        s := "*" + t.String()
        for _, tt := range typesByString(s) {
                p := (*ptrType)(unsafe.Pointer(tt))
                if p.Elem != &t.t {
                        continue
                }
                pi, _ := ptrMap.LoadOrStore(t, p)
                return &pi.(*ptrType).Type
        }

        // Create a new ptrType starting with the description
        // of an *unsafe.Pointer.
        var iptr any = (*unsafe.Pointer)(nil)
        prototype := *(**ptrType)(unsafe.Pointer(&iptr))
        pp := *prototype

        pp.Str = resolveReflectName(newName(s, "", false, false))
        pp.PtrToThis = 0

        // For the type structures linked into the binary, the
        // compiler provides a good hash of the string.
        // Create a good hash for the new string by using
        // the FNV-1 hash's mixing function to combine the
        // old hash and the new "*".
        pp.Hash = fnv1(t.t.Hash, '*')

        pp.Elem = at

        pi, _ := ptrMap.LoadOrStore(t, &pp)
        return &pi.(*ptrType).Type
}

func ptrTo(t *abi.Type) *abi.Type {
        return toRType(t).ptrTo()
}

// fnv1 incorporates the list of bytes into the hash x using the FNV-1 hash function.
func fnv1(x uint32, list ...byte) uint32 {
        for _, b := range list {
                x = x*16777619 ^ uint32(b)
        }
        return x
}

func (t *rtype) Implements(u Type) bool {
        if u == nil {
                panic("reflect: nil type passed to Type.Implements")
        }
        if u.Kind() != Interface {
                panic("reflect: non-interface type passed to Type.Implements")
        }
        return implements(u.common(), t.common())
}

func (t *rtype) AssignableTo(u Type) bool {
        if u == nil {
                panic("reflect: nil type passed to Type.AssignableTo")
        }
        uu := u.common()
        return directlyAssignable(uu, t.common()) || implements(uu, t.common())
}

func (t *rtype) ConvertibleTo(u Type) bool {
        if u == nil {
                panic("reflect: nil type passed to Type.ConvertibleTo")
        }
        return convertOp(u.common(), t.common()) != nil
}

func (t *rtype) Comparable() bool {
        return t.t.Equal != nil
}

// implements reports whether the type V implements the interface type T.
func implements(T, V *abi.Type) bool {
        if T.Kind() != abi.Interface {
                return false
        }
        t := (*interfaceType)(unsafe.Pointer(T))
        if len(t.Methods) == 0 {
                return true
        }

        // The same algorithm applies in both cases, but the
        // method tables for an interface type and a concrete type
        // are different, so the code is duplicated.
        // In both cases the algorithm is a linear scan over the two
        // lists - T's methods and V's methods - simultaneously.
        // Since method tables are stored in a unique sorted order
        // (alphabetical, with no duplicate method names), the scan
        // through V's methods must hit a match for each of T's
        // methods along the way, or else V does not implement T.
        // This lets us run the scan in overall linear time instead of
        // the quadratic time  a naive search would require.
        // See also ../runtime/iface.go.
        if V.Kind() == abi.Interface {
                v := (*interfaceType)(unsafe.Pointer(V))
                i := 0
                for j := 0; j < len(v.Methods); j++ {
                        tm := &t.Methods[i]
                        tmName := t.nameOff(tm.Name)
                        vm := &v.Methods[j]
                        vmName := nameOffFor(V, vm.Name)
                        if vmName.Name() == tmName.Name() && typeOffFor(V, vm.Typ) == t.typeOff(tm.Typ) {
                                if !tmName.IsExported() {
                                        tmPkgPath := pkgPath(tmName)
                                        if tmPkgPath == "" {
                                                tmPkgPath = t.PkgPath.Name()
                                        }
                                        vmPkgPath := pkgPath(vmName)
                                        if vmPkgPath == "" {
                                                vmPkgPath = v.PkgPath.Name()
                                        }
                                        if tmPkgPath != vmPkgPath {
                                                continue
                                        }
                                }
                                if i++; i >= len(t.Methods) {
                                        return true
                                }
                        }
                }
                return false
        }

        v := V.Uncommon()
        if v == nil {
                return false
        }
        i := 0
        vmethods := v.Methods()
        for j := 0; j < int(v.Mcount); j++ {
                tm := &t.Methods[i]
                tmName := t.nameOff(tm.Name)
                vm := vmethods[j]
                vmName := nameOffFor(V, vm.Name)
                if vmName.Name() == tmName.Name() && typeOffFor(V, vm.Mtyp) == t.typeOff(tm.Typ) {
                        if !tmName.IsExported() {
                                tmPkgPath := pkgPath(tmName)
                                if tmPkgPath == "" {
                                        tmPkgPath = t.PkgPath.Name()
                                }
                                vmPkgPath := pkgPath(vmName)
                                if vmPkgPath == "" {
                                        vmPkgPath = nameOffFor(V, v.PkgPath).Name()
                                }
                                if tmPkgPath != vmPkgPath {
                                        continue
                                }
                        }
                        if i++; i >= len(t.Methods) {
                                return true
                        }
                }
        }
        return false
}

// specialChannelAssignability reports whether a value x of channel type V
// can be directly assigned (using memmove) to another channel type T.
// https://golang.org/doc/go_spec.html#Assignability
// T and V must be both of Chan kind.
func specialChannelAssignability(T, V *abi.Type) bool {
        // Special case:
        // x is a bidirectional channel value, T is a channel type,
        // x's type V and T have identical element types,
        // and at least one of V or T is not a defined type.
        return V.ChanDir() == abi.BothDir && (nameFor(T) == "" || nameFor(V) == "") && haveIdenticalType(T.Elem(), V.Elem(), true)
}

// directlyAssignable reports whether a value x of type V can be directly
// assigned (using memmove) to a value of type T.
// https://golang.org/doc/go_spec.html#Assignability
// Ignoring the interface rules (implemented elsewhere)
// and the ideal constant rules (no ideal constants at run time).
func directlyAssignable(T, V *abi.Type) bool {
        // x's type V is identical to T?
        if T == V {
                return true
        }

        // Otherwise at least one of T and V must not be defined
        // and they must have the same kind.
        if T.HasName() && V.HasName() || T.Kind() != V.Kind() {
                return false
        }

        if T.Kind() == abi.Chan && specialChannelAssignability(T, V) {
                return true
        }

        // x's type T and V must have identical underlying types.
        return haveIdenticalUnderlyingType(T, V, true)
}

func haveIdenticalType(T, V *abi.Type, cmpTags bool) bool {
        if cmpTags {
                return T == V
        }

        if nameFor(T) != nameFor(V) || T.Kind() != V.Kind() || pkgPathFor(T) != pkgPathFor(V) {
                return false
        }

        return haveIdenticalUnderlyingType(T, V, false)
}

func haveIdenticalUnderlyingType(T, V *abi.Type, cmpTags bool) bool {
        if T == V {
                return true
        }

        kind := Kind(T.Kind())
        if kind != Kind(V.Kind()) {
                return false
        }

        // Non-composite types of equal kind have same underlying type
        // (the predefined instance of the type).
        if Bool <= kind && kind <= Complex128 || kind == String || kind == UnsafePointer {
                return true
        }

        // Composite types.
        switch kind {
        case Array:
                return T.Len() == V.Len() && haveIdenticalType(T.Elem(), V.Elem(), cmpTags)

        case Chan:
                return V.ChanDir() == T.ChanDir() && haveIdenticalType(T.Elem(), V.Elem(), cmpTags)

        case Func:
                t := (*funcType)(unsafe.Pointer(T))
                v := (*funcType)(unsafe.Pointer(V))
                if t.OutCount != v.OutCount || t.InCount != v.InCount {
                        return false
                }
                for i := 0; i < t.NumIn(); i++ {
                        if !haveIdenticalType(t.In(i), v.In(i), cmpTags) {
                                return false
                        }
                }
                for i := 0; i < t.NumOut(); i++ {
                        if !haveIdenticalType(t.Out(i), v.Out(i), cmpTags) {
                                return false
                        }
                }
                return true

        case Interface:
                t := (*interfaceType)(unsafe.Pointer(T))
                v := (*interfaceType)(unsafe.Pointer(V))
                if len(t.Methods) == 0 && len(v.Methods) == 0 {
                        return true
                }
                // Might have the same methods but still
                // need a run time conversion.
                return false

        case Map:
                return haveIdenticalType(T.Key(), V.Key(), cmpTags) && haveIdenticalType(T.Elem(), V.Elem(), cmpTags)

        case Pointer, Slice:
                return haveIdenticalType(T.Elem(), V.Elem(), cmpTags)

        case Struct:
                t := (*structType)(unsafe.Pointer(T))
                v := (*structType)(unsafe.Pointer(V))
                if len(t.Fields) != len(v.Fields) {
                        return false
                }
                if t.PkgPath.Name() != v.PkgPath.Name() {
                        return false
                }
                for i := range t.Fields {
                        tf := &t.Fields[i]
                        vf := &v.Fields[i]
                        if tf.Name.Name() != vf.Name.Name() {
                                return false
                        }
                        if !haveIdenticalType(tf.Typ, vf.Typ, cmpTags) {
                                return false
                        }
                        if cmpTags && tf.Name.Tag() != vf.Name.Tag() {
                                return false
                        }
                        if tf.Offset != vf.Offset {
                                return false
                        }
                        if tf.Embedded() != vf.Embedded() {
                                return false
                        }
                }
                return true
        }

        return false
}

// typelinks is implemented in package runtime.
// It returns a slice of the sections in each module,
// and a slice of *rtype offsets in each module.
//
// The types in each module are sorted by string. That is, the first
// two linked types of the first module are:
//
//      d0 := sections[0]
//      t1 := (*rtype)(add(d0, offset[0][0]))
//      t2 := (*rtype)(add(d0, offset[0][1]))
//
// and
//
//      t1.String() < t2.String()
//
// Note that strings are not unique identifiers for types:
// there can be more than one with a given string.
// Only types we might want to look up are included:
// pointers, channels, maps, slices, and arrays.
func typelinks() (sections []unsafe.Pointer, offset [][]int32)

func rtypeOff(section unsafe.Pointer, off int32) *abi.Type {
        return (*abi.Type)(add(section, uintptr(off), "sizeof(rtype) > 0"))
}

// typesByString returns the subslice of typelinks() whose elements have
// the given string representation.
// It may be empty (no known types with that string) or may have
// multiple elements (multiple types with that string).
func typesByString(s string) []*abi.Type {
        sections, offset := typelinks()
        var ret []*abi.Type

        for offsI, offs := range offset {
                section := sections[offsI]

                // We are looking for the first index i where the string becomes >= s.
                // This is a copy of sort.Search, with f(h) replaced by (*typ[h].String() >= s).
                i, j := 0, len(offs)
                for i < j {
                        h := int(uint(i+j) >> 1) // avoid overflow when computing h
                        // i ≤ h < j
                        if !(stringFor(rtypeOff(section, offs[h])) >= s) {
                                i = h + 1 // preserves f(i-1) == false
                        } else {
                                j = h // preserves f(j) == true
                        }
                }
                // i == j, f(i-1) == false, and f(j) (= f(i)) == true  =>  answer is i.

                // Having found the first, linear scan forward to find the last.
                // We could do a second binary search, but the caller is going
                // to do a linear scan anyway.
                for j := i; j < len(offs); j++ {
                        typ := rtypeOff(section, offs[j])
                        if stringFor(typ) != s {
                                break
                        }
                        ret = append(ret, typ)
                }
        }
        return ret
}

// The lookupCache caches ArrayOf, ChanOf, MapOf and SliceOf lookups.
var lookupCache sync.Map // map[cacheKey]*rtype

// A cacheKey is the key for use in the lookupCache.
// Four values describe any of the types we are looking for:
// type kind, one or two subtypes, and an extra integer.
type cacheKey struct {
        kind  Kind
        t1    *abi.Type
        t2    *abi.Type
        extra uintptr
}

// The funcLookupCache caches FuncOf lookups.
// FuncOf does not share the common lookupCache since cacheKey is not
// sufficient to represent functions unambiguously.
var funcLookupCache struct {
        sync.Mutex // Guards stores (but not loads) on m.

        // m is a map[uint32][]*rtype keyed by the hash calculated in FuncOf.
        // Elements of m are append-only and thus safe for concurrent reading.
        m sync.Map
}

// ChanOf returns the channel type with the given direction and element type.
// For example, if t represents int, ChanOf(RecvDir, t) represents <-chan int.
//
// The gc runtime imposes a limit of 64 kB on channel element types.
// If t's size is equal to or exceeds this limit, ChanOf panics.
func ChanOf(dir ChanDir, t Type) Type {
        typ := t.common()

        // Look in cache.
        ckey := cacheKey{Chan, typ, nil, uintptr(dir)}
        if ch, ok := lookupCache.Load(ckey); ok {
                return ch.(*rtype)
        }

        // This restriction is imposed by the gc compiler and the runtime.
        if typ.Size_ >= 1<<16 {
                panic("reflect.ChanOf: element size too large")
        }

        // Look in known types.
        var s string
        switch dir {
        default:
                panic("reflect.ChanOf: invalid dir")
        case SendDir:
                s = "chan<- " + stringFor(typ)
        case RecvDir:
                s = "<-chan " + stringFor(typ)
        case BothDir:
                typeStr := stringFor(typ)
                if typeStr[0] == '<' {
                        // typ is recv chan, need parentheses as "<-" associates with leftmost
                        // chan possible, see:
                        // * https://golang.org/ref/spec#Channel_types
                        // * https://github.com/golang/go/issues/39897
                        s = "chan (" + typeStr + ")"
                } else {
                        s = "chan " + typeStr
                }
        }
        for _, tt := range typesByString(s) {
                ch := (*chanType)(unsafe.Pointer(tt))
                if ch.Elem == typ && ch.Dir == abi.ChanDir(dir) {
                        ti, _ := lookupCache.LoadOrStore(ckey, toRType(tt))
                        return ti.(Type)
                }
        }

        // Make a channel type.
        var ichan any = (chan unsafe.Pointer)(nil)
        prototype := *(**chanType)(unsafe.Pointer(&ichan))
        ch := *prototype
        ch.TFlag = abi.TFlagRegularMemory
        ch.Dir = abi.ChanDir(dir)
        ch.Str = resolveReflectName(newName(s, "", false, false))
        ch.Hash = fnv1(typ.Hash, 'c', byte(dir))
        ch.Elem = typ

        ti, _ := lookupCache.LoadOrStore(ckey, toRType(&ch.Type))
        return ti.(Type)
}

// MapOf returns the map type with the given key and element types.
// For example, if k represents int and e represents string,
// MapOf(k, e) represents map[int]string.
//
// If the key type is not a valid map key type (that is, if it does
// not implement Go's == operator), MapOf panics.
func MapOf(key, elem Type) Type {
        ktyp := key.common()
        etyp := elem.common()

        if ktyp.Equal == nil {
                panic("reflect.MapOf: invalid key type " + stringFor(ktyp))
        }

        // Look in cache.
        ckey := cacheKey{Map, ktyp, etyp, 0}
        if mt, ok := lookupCache.Load(ckey); ok {
                return mt.(Type)
        }

        // Look in known types.
        s := "map[" + stringFor(ktyp) + "]" + stringFor(etyp)
        for _, tt := range typesByString(s) {
                mt := (*mapType)(unsafe.Pointer(tt))
                if mt.Key == ktyp && mt.Elem == etyp {
                        ti, _ := lookupCache.LoadOrStore(ckey, toRType(tt))
                        return ti.(Type)
                }
        }

        // Make a map type.
        // Note: flag values must match those used in the TMAP case
        // in ../cmd/compile/internal/reflectdata/reflect.go:writeType.
        var imap any = (map[unsafe.Pointer]unsafe.Pointer)(nil)
        mt := **(**mapType)(unsafe.Pointer(&imap))
        mt.Str = resolveReflectName(newName(s, "", false, false))
        mt.TFlag = 0
        mt.Hash = fnv1(etyp.Hash, 'm', byte(ktyp.Hash>>24), byte(ktyp.Hash>>16), byte(ktyp.Hash>>8), byte(ktyp.Hash))
        mt.Key = ktyp
        mt.Elem = etyp
        mt.Bucket = bucketOf(ktyp, etyp)
        mt.Hasher = func(p unsafe.Pointer, seed uintptr) uintptr {
                return typehash(ktyp, p, seed)
        }
        mt.Flags = 0
        if ktyp.Size_ > maxKeySize {
                mt.KeySize = uint8(goarch.PtrSize)
                mt.Flags |= 1 // indirect key
        } else {
                mt.KeySize = uint8(ktyp.Size_)
        }
        if etyp.Size_ > maxValSize {
                mt.ValueSize = uint8(goarch.PtrSize)
                mt.Flags |= 2 // indirect value
        } else {
                mt.MapType.ValueSize = uint8(etyp.Size_)
        }
        mt.MapType.BucketSize = uint16(mt.Bucket.Size_)
        if isReflexive(ktyp) {
                mt.Flags |= 4
        }
        if needKeyUpdate(ktyp) {
                mt.Flags |= 8
        }
        if hashMightPanic(ktyp) {
                mt.Flags |= 16
        }
        mt.PtrToThis = 0

        ti, _ := lookupCache.LoadOrStore(ckey, toRType(&mt.Type))
        return ti.(Type)
}

var funcTypes []Type
var funcTypesMutex sync.Mutex

func initFuncTypes(n int) Type {
        funcTypesMutex.Lock()
        defer funcTypesMutex.Unlock()
        if n >= len(funcTypes) {
                newFuncTypes := make([]Type, n+1)
                copy(newFuncTypes, funcTypes)
                funcTypes = newFuncTypes
        }
        if funcTypes[n] != nil {
                return funcTypes[n]
        }

        funcTypes[n] = StructOf([]StructField{
                {
                        Name: "FuncType",
                        Type: TypeOf(funcType{}),
                },
                {
                        Name: "Args",
                        Type: ArrayOf(n, TypeOf(&rtype{})),
                },
        })
        return funcTypes[n]
}

// FuncOf returns the function type with the given argument and result types.
// For example if k represents int and e represents string,
// FuncOf([]Type{k}, []Type{e}, false) represents func(int) string.
//
// The variadic argument controls whether the function is variadic. FuncOf
// panics if the in[len(in)-1] does not represent a slice and variadic is
// true.
func FuncOf(in, out []Type, variadic bool) Type {
        if variadic && (len(in) == 0 || in[len(in)-1].Kind() != Slice) {
                panic("reflect.FuncOf: last arg of variadic func must be slice")
        }

        // Make a func type.
        var ifunc any = (func())(nil)
        prototype := *(**funcType)(unsafe.Pointer(&ifunc))
        n := len(in) + len(out)

        if n > 128 {
                panic("reflect.FuncOf: too many arguments")
        }

        o := New(initFuncTypes(n)).Elem()
        ft := (*funcType)(unsafe.Pointer(o.Field(0).Addr().Pointer()))
        args := unsafe.Slice((**rtype)(unsafe.Pointer(o.Field(1).Addr().Pointer())), n)[0:0:n]
        *ft = *prototype

        // Build a hash and minimally populate ft.
        var hash uint32
        for _, in := range in {
                t := in.(*rtype)
                args = append(args, t)
                hash = fnv1(hash, byte(t.t.Hash>>24), byte(t.t.Hash>>16), byte(t.t.Hash>>8), byte(t.t.Hash))
        }
        if variadic {
                hash = fnv1(hash, 'v')
        }
        hash = fnv1(hash, '.')
        for _, out := range out {
                t := out.(*rtype)
                args = append(args, t)
                hash = fnv1(hash, byte(t.t.Hash>>24), byte(t.t.Hash>>16), byte(t.t.Hash>>8), byte(t.t.Hash))
        }

        ft.TFlag = 0
        ft.Hash = hash
        ft.InCount = uint16(len(in))
        ft.OutCount = uint16(len(out))
        if variadic {
                ft.OutCount |= 1 << 15
        }

        // Look in cache.
        if ts, ok := funcLookupCache.m.Load(hash); ok {
                for _, t := range ts.([]*abi.Type) {
                        if haveIdenticalUnderlyingType(&ft.Type, t, true) {
                                return toRType(t)
                        }
                }
        }

        // Not in cache, lock and retry.
        funcLookupCache.Lock()
        defer funcLookupCache.Unlock()
        if ts, ok := funcLookupCache.m.Load(hash); ok {
                for _, t := range ts.([]*abi.Type) {
                        if haveIdenticalUnderlyingType(&ft.Type, t, true) {
                                return toRType(t)
                        }
                }
        }

        addToCache := func(tt *abi.Type) Type {
                var rts []*abi.Type
                if rti, ok := funcLookupCache.m.Load(hash); ok {
                        rts = rti.([]*abi.Type)
                }
                funcLookupCache.m.Store(hash, append(rts, tt))
                return toType(tt)
        }

        // Look in known types for the same string representation.
        str := funcStr(ft)
        for _, tt := range typesByString(str) {
                if haveIdenticalUnderlyingType(&ft.Type, tt, true) {
                        return addToCache(tt)
                }
        }

        // Populate the remaining fields of ft and store in cache.
        ft.Str = resolveReflectName(newName(str, "", false, false))
        ft.PtrToThis = 0
        return addToCache(&ft.Type)
}
func stringFor(t *abi.Type) string {
        return toRType(t).String()
}

// funcStr builds a string representation of a funcType.
func funcStr(ft *funcType) string {
        repr := make([]byte, 0, 64)
        repr = append(repr, "func("...)
        for i, t := range ft.InSlice() {
                if i > 0 {
                        repr = append(repr, ", "...)
                }
                if ft.IsVariadic() && i == int(ft.InCount)-1 {
                        repr = append(repr, "..."...)
                        repr = append(repr, stringFor((*sliceType)(unsafe.Pointer(t)).Elem)...)
                } else {
                        repr = append(repr, stringFor(t)...)
                }
        }
        repr = append(repr, ')')
        out := ft.OutSlice()
        if len(out) == 1 {
                repr = append(repr, ' ')
        } else if len(out) > 1 {
                repr = append(repr, " ("...)
        }
        for i, t := range out {
                if i > 0 {
                        repr = append(repr, ", "...)
                }
                repr = append(repr, stringFor(t)...)
        }
        if len(out) > 1 {
                repr = append(repr, ')')
        }
        return string(repr)
}

// isReflexive reports whether the == operation on the type is reflexive.
// That is, x == x for all values x of type t.
func isReflexive(t *abi.Type) bool {
        switch Kind(t.Kind()) {
        case Bool, Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr, Chan, Pointer, String, UnsafePointer:
                return true
        case Float32, Float64, Complex64, Complex128, Interface:
                return false
        case Array:
                tt := (*arrayType)(unsafe.Pointer(t))
                return isReflexive(tt.Elem)
        case Struct:
                tt := (*structType)(unsafe.Pointer(t))
                for _, f := range tt.Fields {
                        if !isReflexive(f.Typ) {
                                return false
                        }
                }
                return true
        default:
                // Func, Map, Slice, Invalid
                panic("isReflexive called on non-key type " + stringFor(t))
        }
}

// needKeyUpdate reports whether map overwrites require the key to be copied.
func needKeyUpdate(t *abi.Type) bool {
        switch Kind(t.Kind()) {
        case Bool, Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr, Chan, Pointer, UnsafePointer:
                return false
        case Float32, Float64, Complex64, Complex128, Interface, String:
                // Float keys can be updated from +0 to -0.
                // String keys can be updated to use a smaller backing store.
                // Interfaces might have floats of strings in them.
                return true
        case Array:
                tt := (*arrayType)(unsafe.Pointer(t))
                return needKeyUpdate(tt.Elem)
        case Struct:
                tt := (*structType)(unsafe.Pointer(t))
                for _, f := range tt.Fields {
                        if needKeyUpdate(f.Typ) {
                                return true
                        }
                }
                return false
        default:
                // Func, Map, Slice, Invalid
                panic("needKeyUpdate called on non-key type " + stringFor(t))
        }
}

// hashMightPanic reports whether the hash of a map key of type t might panic.
func hashMightPanic(t *abi.Type) bool {
        switch Kind(t.Kind()) {
        case Interface:
                return true
        case Array:
                tt := (*arrayType)(unsafe.Pointer(t))
                return hashMightPanic(tt.Elem)
        case Struct:
                tt := (*structType)(unsafe.Pointer(t))
                for _, f := range tt.Fields {
                        if hashMightPanic(f.Typ) {
                                return true
                        }
                }
                return false
        default:
                return false
        }
}

// Make sure these routines stay in sync with ../runtime/map.go!
// These types exist only for GC, so we only fill out GC relevant info.
// Currently, that's just size and the GC program. We also fill in string
// for possible debugging use.
const (
        bucketSize uintptr = abi.MapBucketCount
        maxKeySize uintptr = abi.MapMaxKeyBytes
        maxValSize uintptr = abi.MapMaxElemBytes
)

func bucketOf(ktyp, etyp *abi.Type) *abi.Type {
        if ktyp.Size_ > maxKeySize {
                ktyp = ptrTo(ktyp)
        }
        if etyp.Size_ > maxValSize {
                etyp = ptrTo(etyp)
        }

        // Prepare GC data if any.
        // A bucket is at most bucketSize*(1+maxKeySize+maxValSize)+ptrSize bytes,
        // or 2064 bytes, or 258 pointer-size words, or 33 bytes of pointer bitmap.
        // Note that since the key and value are known to be <= 128 bytes,
        // they're guaranteed to have bitmaps instead of GC programs.
        var gcdata *byte
        var ptrdata uintptr

        size := bucketSize*(1+ktyp.Size_+etyp.Size_) + goarch.PtrSize
        if size&uintptr(ktyp.Align_-1) != 0 || size&uintptr(etyp.Align_-1) != 0 {
                panic("reflect: bad size computation in MapOf")
        }

        if ktyp.PtrBytes != 0 || etyp.PtrBytes != 0 {
                nptr := (bucketSize*(1+ktyp.Size_+etyp.Size_) + goarch.PtrSize) / goarch.PtrSize
                n := (nptr + 7) / 8

                // Runtime needs pointer masks to be a multiple of uintptr in size.
                n = (n + goarch.PtrSize - 1) &^ (goarch.PtrSize - 1)
                mask := make([]byte, n)
                base := bucketSize / goarch.PtrSize

                if ktyp.PtrBytes != 0 {
                        emitGCMask(mask, base, ktyp, bucketSize)
                }
                base += bucketSize * ktyp.Size_ / goarch.PtrSize

                if etyp.PtrBytes != 0 {
                        emitGCMask(mask, base, etyp, bucketSize)
                }
                base += bucketSize * etyp.Size_ / goarch.PtrSize

                word := base
                mask[word/8] |= 1 << (word % 8)
                gcdata = &mask[0]
                ptrdata = (word + 1) * goarch.PtrSize

                // overflow word must be last
                if ptrdata != size {
                        panic("reflect: bad layout computation in MapOf")
                }
        }

        b := &abi.Type{
                Align_:   goarch.PtrSize,
                Size_:    size,
                Kind_:    uint8(Struct),
                PtrBytes: ptrdata,
                GCData:   gcdata,
        }
        s := "bucket(" + stringFor(ktyp) + "," + stringFor(etyp) + ")"
        b.Str = resolveReflectName(newName(s, "", false, false))
        return b
}

func (t *rtype) gcSlice(begin, end uintptr) []byte {
        return (*[1 << 30]byte)(unsafe.Pointer(t.t.GCData))[begin:end:end]
}

// emitGCMask writes the GC mask for [n]typ into out, starting at bit
// offset base.
func emitGCMask(out []byte, base uintptr, typ *abi.Type, n uintptr) {
        if typ.Kind_&kindGCProg != 0 {
                panic("reflect: unexpected GC program")
        }
        ptrs := typ.PtrBytes / goarch.PtrSize
        words := typ.Size_ / goarch.PtrSize
        mask := typ.GcSlice(0, (ptrs+7)/8)
        for j := uintptr(0); j < ptrs; j++ {
                if (mask[j/8]>>(j%8))&1 != 0 {
                        for i := uintptr(0); i < n; i++ {
                                k := base + i*words + j
                                out[k/8] |= 1 << (k % 8)
                        }
                }
        }
}

// appendGCProg appends the GC program for the first ptrdata bytes of
// typ to dst and returns the extended slice.
func appendGCProg(dst []byte, typ *abi.Type) []byte {
        if typ.Kind_&kindGCProg != 0 {
                // Element has GC program; emit one element.
                n := uintptr(*(*uint32)(unsafe.Pointer(typ.GCData)))
                prog := typ.GcSlice(4, 4+n-1)
                return append(dst, prog...)
        }

        // Element is small with pointer mask; use as literal bits.
        ptrs := typ.PtrBytes / goarch.PtrSize
        mask := typ.GcSlice(0, (ptrs+7)/8)

        // Emit 120-bit chunks of full bytes (max is 127 but we avoid using partial bytes).
        for ; ptrs > 120; ptrs -= 120 {
                dst = append(dst, 120)
                dst = append(dst, mask[:15]...)
                mask = mask[15:]
        }

        dst = append(dst, byte(ptrs))
        dst = append(dst, mask...)
        return dst
}

// SliceOf returns the slice type with element type t.
// For example, if t represents int, SliceOf(t) represents []int.
func SliceOf(t Type) Type {
        typ := t.common()

        // Look in cache.
        ckey := cacheKey{Slice, typ, nil, 0}
        if slice, ok := lookupCache.Load(ckey); ok {
                return slice.(Type)
        }

        // Look in known types.
        s := "[]" + stringFor(typ)
        for _, tt := range typesByString(s) {
                slice := (*sliceType)(unsafe.Pointer(tt))
                if slice.Elem == typ {
                        ti, _ := lookupCache.LoadOrStore(ckey, toRType(tt))
                        return ti.(Type)
                }
        }

        // Make a slice type.
        var islice any = ([]unsafe.Pointer)(nil)
        prototype := *(**sliceType)(unsafe.Pointer(&islice))
        slice := *prototype
        slice.TFlag = 0
        slice.Str = resolveReflectName(newName(s, "", false, false))
        slice.Hash = fnv1(typ.Hash, '[')
        slice.Elem = typ
        slice.PtrToThis = 0

        ti, _ := lookupCache.LoadOrStore(ckey, toRType(&slice.Type))
        return ti.(Type)
}

// The structLookupCache caches StructOf lookups.
// StructOf does not share the common lookupCache since we need to pin
// the memory associated with *structTypeFixedN.
var structLookupCache struct {
        sync.Mutex // Guards stores (but not loads) on m.

        // m is a map[uint32][]Type keyed by the hash calculated in StructOf.
        // Elements in m are append-only and thus safe for concurrent reading.
        m sync.Map
}

type structTypeUncommon struct {
        structType
        u uncommonType
}

// isLetter reports whether a given 'rune' is classified as a Letter.
func isLetter(ch rune) bool {
        return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch >= utf8.RuneSelf && unicode.IsLetter(ch)
}

// isValidFieldName checks if a string is a valid (struct) field name or not.
//
// According to the language spec, a field name should be an identifier.
//
// identifier = letter { letter | unicode_digit } .
// letter = unicode_letter | "_" .
func isValidFieldName(fieldName string) bool {
        for i, c := range fieldName {
                if i == 0 && !isLetter(c) {
                        return false
                }

                if !(isLetter(c) || unicode.IsDigit(c)) {
                        return false
                }
        }

        return len(fieldName) > 0
}

// StructOf returns the struct type containing fields.
// The Offset and Index fields are ignored and computed as they would be
// by the compiler.
//
// StructOf currently does not support promoted methods of embedded fields
// and panics if passed unexported StructFields.
func StructOf(fields []StructField) Type {
        var (
                hash       = fnv1(0, []byte("struct {")...)
                size       uintptr
                typalign   uint8
                comparable = true
                methods    []abi.Method

                fs   = make([]structField, len(fields))
                repr = make([]byte, 0, 64)
                fset = map[string]struct{}{} // fields' names

                hasGCProg = false // records whether a struct-field type has a GCProg
        )

        lastzero := uintptr(0)
        repr = append(repr, "struct {"...)
        pkgpath := ""
        for i, field := range fields {
                if field.Name == "" {
                        panic("reflect.StructOf: field " + strconv.Itoa(i) + " has no name")
                }
                if !isValidFieldName(field.Name) {
                        panic("reflect.StructOf: field " + strconv.Itoa(i) + " has invalid name")
                }
                if field.Type == nil {
                        panic("reflect.StructOf: field " + strconv.Itoa(i) + " has no type")
                }
                f, fpkgpath := runtimeStructField(field)
                ft := f.Typ
                if ft.Kind_&kindGCProg != 0 {
                        hasGCProg = true
                }
                if fpkgpath != "" {
                        if pkgpath == "" {
                                pkgpath = fpkgpath
                        } else if pkgpath != fpkgpath {
                                panic("reflect.Struct: fields with different PkgPath " + pkgpath + " and " + fpkgpath)
                        }
                }

                // Update string and hash
                name := f.Name.Name()
                hash = fnv1(hash, []byte(name)...)
                repr = append(repr, (" " + name)...)
                if f.Embedded() {
                        // Embedded field
                        if f.Typ.Kind() == abi.Pointer {
                                // Embedded ** and *interface{} are illegal
                                elem := ft.Elem()
                                if k := elem.Kind(); k == abi.Pointer || k == abi.Interface {
                                        panic("reflect.StructOf: illegal embedded field type " + stringFor(ft))
                                }
                        }

                        switch Kind(f.Typ.Kind()) {
                        case Interface:
                                ift := (*interfaceType)(unsafe.Pointer(ft))
                                for _, m := range ift.Methods {
                                        if pkgPath(ift.nameOff(m.Name)) != "" {
                                                // TODO(sbinet).  Issue 15924.
                                                panic("reflect: embedded interface with unexported method(s) not implemented")
                                        }

                                        fnStub := resolveReflectText(unsafe.Pointer(abi.FuncPCABIInternal(embeddedIfaceMethStub)))
                                        methods = append(methods, abi.Method{
                                                Name: resolveReflectName(ift.nameOff(m.Name)),
                                                Mtyp: resolveReflectType(ift.typeOff(m.Typ)),
                                                Ifn:  fnStub,
                                                Tfn:  fnStub,
                                        })
                                }
                        case Pointer:
                                ptr := (*ptrType)(unsafe.Pointer(ft))
                                if unt := ptr.Uncommon(); unt != nil {
                                        if i > 0 && unt.Mcount > 0 {
                                                // Issue 15924.
                                                panic("reflect: embedded type with methods not implemented if type is not first field")
                                        }
                                        if len(fields) > 1 {
                                                panic("reflect: embedded type with methods not implemented if there is more than one field")
                                        }
                                        for _, m := range unt.Methods() {
                                                mname := nameOffFor(ft, m.Name)
                                                if pkgPath(mname) != "" {
                                                        // TODO(sbinet).
                                                        // Issue 15924.
                                                        panic("reflect: embedded interface with unexported method(s) not implemented")
                                                }
                                                methods = append(methods, abi.Method{
                                                        Name: resolveReflectName(mname),
                                                        Mtyp: resolveReflectType(typeOffFor(ft, m.Mtyp)),
                                                        Ifn:  resolveReflectText(textOffFor(ft, m.Ifn)),
                                                        Tfn:  resolveReflectText(textOffFor(ft, m.Tfn)),
                                                })
                                        }
                                }
                                if unt := ptr.Elem.Uncommon(); unt != nil {
                                        for _, m := range unt.Methods() {
                                                mname := nameOffFor(ft, m.Name)
                                                if pkgPath(mname) != "" {
                                                        // TODO(sbinet)
                                                        // Issue 15924.
                                                        panic("reflect: embedded interface with unexported method(s) not implemented")
                                                }
                                                methods = append(methods, abi.Method{
                                                        Name: resolveReflectName(mname),
                                                        Mtyp: resolveReflectType(typeOffFor(ptr.Elem, m.Mtyp)),
                                                        Ifn:  resolveReflectText(textOffFor(ptr.Elem, m.Ifn)),
                                                        Tfn:  resolveReflectText(textOffFor(ptr.Elem, m.Tfn)),
                                                })
                                        }
                                }
                        default:
                                if unt := ft.Uncommon(); unt != nil {
                                        if i > 0 && unt.Mcount > 0 {
                                                // Issue 15924.
                                                panic("reflect: embedded type with methods not implemented if type is not first field")
                                        }
                                        if len(fields) > 1 && ft.Kind_&kindDirectIface != 0 {
                                                panic("reflect: embedded type with methods not implemented for non-pointer type")
                                        }
                                        for _, m := range unt.Methods() {
                                                mname := nameOffFor(ft, m.Name)
                                                if pkgPath(mname) != "" {
                                                        // TODO(sbinet)
                                                        // Issue 15924.
                                                        panic("reflect: embedded interface with unexported method(s) not implemented")
                                                }
                                                methods = append(methods, abi.Method{
                                                        Name: resolveReflectName(mname),
                                                        Mtyp: resolveReflectType(typeOffFor(ft, m.Mtyp)),
                                                        Ifn:  resolveReflectText(textOffFor(ft, m.Ifn)),
                                                        Tfn:  resolveReflectText(textOffFor(ft, m.Tfn)),
                                                })

                                        }
                                }
                        }
                }
                if _, dup := fset[name]; dup && name != "_" {
                        panic("reflect.StructOf: duplicate field " + name)
                }
                fset[name] = struct{}{}

                hash = fnv1(hash, byte(ft.Hash>>24), byte(ft.Hash>>16), byte(ft.Hash>>8), byte(ft.Hash))

                repr = append(repr, (" " + stringFor(ft))...)
                if f.Name.HasTag() {
                        hash = fnv1(hash, []byte(f.Name.Tag())...)
                        repr = append(repr, (" " + strconv.Quote(f.Name.Tag()))...)
                }
                if i < len(fields)-1 {
                        repr = append(repr, ';')
                }

                comparable = comparable && (ft.Equal != nil)

                offset := align(size, uintptr(ft.Align_))
                if offset < size {
                        panic("reflect.StructOf: struct size would exceed virtual address space")
                }
                if ft.Align_ > typalign {
                        typalign = ft.Align_
                }
                size = offset + ft.Size_
                if size < offset {
                        panic("reflect.StructOf: struct size would exceed virtual address space")
                }
                f.Offset = offset

                if ft.Size_ == 0 {
                        lastzero = size
                }

                fs[i] = f
        }

        if size > 0 && lastzero == size {
                // This is a non-zero sized struct that ends in a
                // zero-sized field. We add an extra byte of padding,
                // to ensure that taking the address of the final
                // zero-sized field can't manufacture a pointer to the
                // next object in the heap. See issue 9401.
                size++
                if size == 0 {
                        panic("reflect.StructOf: struct size would exceed virtual address space")
                }
        }

        var typ *structType
        var ut *uncommonType

        if len(methods) == 0 {
                t := new(structTypeUncommon)
                typ = &t.structType
                ut = &t.u
        } else {
                // A *rtype representing a struct is followed directly in memory by an
                // array of method objects representing the methods attached to the
                // struct. To get the same layout for a run time generated type, we
                // need an array directly following the uncommonType memory.
                // A similar strategy is used for funcTypeFixed4, ...funcTypeFixedN.
                tt := New(StructOf([]StructField{
                        {Name: "S", Type: TypeOf(structType{})},
                        {Name: "U", Type: TypeOf(uncommonType{})},
                        {Name: "M", Type: ArrayOf(len(methods), TypeOf(methods[0]))},
                }))

                typ = (*structType)(tt.Elem().Field(0).Addr().UnsafePointer())
                ut = (*uncommonType)(tt.Elem().Field(1).Addr().UnsafePointer())

                copy(tt.Elem().Field(2).Slice(0, len(methods)).Interface().([]abi.Method), methods)
        }
        // TODO(sbinet): Once we allow embedding multiple types,
        // methods will need to be sorted like the compiler does.
        // TODO(sbinet): Once we allow non-exported methods, we will
        // need to compute xcount as the number of exported methods.
        ut.Mcount = uint16(len(methods))
        ut.Xcount = ut.Mcount
        ut.Moff = uint32(unsafe.Sizeof(uncommonType{}))

        if len(fs) > 0 {
                repr = append(repr, ' ')
        }
        repr = append(repr, '}')
        hash = fnv1(hash, '}')
        str := string(repr)

        // Round the size up to be a multiple of the alignment.
        s := align(size, uintptr(typalign))
        if s < size {
                panic("reflect.StructOf: struct size would exceed virtual address space")
        }
        size = s

        // Make the struct type.
        var istruct any = struct{}{}
        prototype := *(**structType)(unsafe.Pointer(&istruct))
        *typ = *prototype
        typ.Fields = fs
        if pkgpath != "" {
                typ.PkgPath = newName(pkgpath, "", false, false)
        }

        // Look in cache.
        if ts, ok := structLookupCache.m.Load(hash); ok {
                for _, st := range ts.([]Type) {
                        t := st.common()
                        if haveIdenticalUnderlyingType(&typ.Type, t, true) {
                                return toType(t)
                        }
                }
        }

        // Not in cache, lock and retry.
        structLookupCache.Lock()
        defer structLookupCache.Unlock()
        if ts, ok := structLookupCache.m.Load(hash); ok {
                for _, st := range ts.([]Type) {
                        t := st.common()
                        if haveIdenticalUnderlyingType(&typ.Type, t, true) {
                                return toType(t)
                        }
                }
        }

        addToCache := func(t Type) Type {
                var ts []Type
                if ti, ok := structLookupCache.m.Load(hash); ok {
                        ts = ti.([]Type)
                }
                structLookupCache.m.Store(hash, append(ts, t))
                return t
        }

        // Look in known types.
        for _, t := range typesByString(str) {
                if haveIdenticalUnderlyingType(&typ.Type, t, true) {
                        // even if 't' wasn't a structType with methods, we should be ok
                        // as the 'u uncommonType' field won't be accessed except when
                        // tflag&abi.TFlagUncommon is set.
                        return addToCache(toType(t))
                }
        }

        typ.Str = resolveReflectName(newName(str, "", false, false))
        typ.TFlag = 0 // TODO: set tflagRegularMemory
        typ.Hash = hash
        typ.Size_ = size
        typ.PtrBytes = typeptrdata(&typ.Type)
        typ.Align_ = typalign
        typ.FieldAlign_ = typalign
        typ.PtrToThis = 0
        if len(methods) > 0 {
                typ.TFlag |= abi.TFlagUncommon
        }

        if hasGCProg {
                lastPtrField := 0
                for i, ft := range fs {
                        if ft.Typ.Pointers() {
                                lastPtrField = i
                        }
                }
                prog := []byte{0, 0, 0, 0} // will be length of prog
                var off uintptr
                for i, ft := range fs {
                        if i > lastPtrField {
                                // gcprog should not include anything for any field after
                                // the last field that contains pointer data
                                break
                        }
                        if !ft.Typ.Pointers() {
                                // Ignore pointerless fields.
                                continue
                        }
                        // Pad to start of this field with zeros.
                        if ft.Offset > off {
                                n := (ft.Offset - off) / goarch.PtrSize
                                prog = append(prog, 0x01, 0x00) // emit a 0 bit
                                if n > 1 {
                                        prog = append(prog, 0x81)      // repeat previous bit
                                        prog = appendVarint(prog, n-1) // n-1 times
                                }
                                off = ft.Offset
                        }

                        prog = appendGCProg(prog, ft.Typ)
                        off += ft.Typ.PtrBytes
                }
                prog = append(prog, 0)
                *(*uint32)(unsafe.Pointer(&prog[0])) = uint32(len(prog) - 4)
                typ.Kind_ |= kindGCProg
                typ.GCData = &prog[0]
        } else {
                typ.Kind_ &^= kindGCProg
                bv := new(bitVector)
                addTypeBits(bv, 0, &typ.Type)
                if len(bv.data) > 0 {
                        typ.GCData = &bv.data[0]
                }
        }
        typ.Equal = nil
        if comparable {
                typ.Equal = func(p, q unsafe.Pointer) bool {
                        for _, ft := range typ.Fields {
                                pi := add(p, ft.Offset, "&x.field safe")
                                qi := add(q, ft.Offset, "&x.field safe")
                                if !ft.Typ.Equal(pi, qi) {
                                        return false
                                }
                        }
                        return true
                }
        }

        switch {
        case len(fs) == 1 && !ifaceIndir(fs[0].Typ):
                // structs of 1 direct iface type can be direct
                typ.Kind_ |= kindDirectIface
        default:
                typ.Kind_ &^= kindDirectIface
        }

        return addToCache(toType(&typ.Type))
}

func embeddedIfaceMethStub() {
        panic("reflect: StructOf does not support methods of embedded interfaces")
}

// runtimeStructField takes a StructField value passed to StructOf and
// returns both the corresponding internal representation, of type
// structField, and the pkgpath value to use for this field.
func runtimeStructField(field StructField) (structField, string) {
        if field.Anonymous && field.PkgPath != "" {
                panic("reflect.StructOf: field \"" + field.Name + "\" is anonymous but has PkgPath set")
        }

        if field.IsExported() {
                // Best-effort check for misuse.
                // Since this field will be treated as exported, not much harm done if Unicode lowercase slips through.
                c := field.Name[0]
                if 'a' <= c && c <= 'z' || c == '_' {
                        panic("reflect.StructOf: field \"" + field.Name + "\" is unexported but missing PkgPath")
                }
        }

        resolveReflectType(field.Type.common()) // install in runtime
        f := structField{
                Name:   newName(field.Name, string(field.Tag), field.IsExported(), field.Anonymous),
                Typ:    field.Type.common(),
                Offset: 0,
        }
        return f, field.PkgPath
}

// typeptrdata returns the length in bytes of the prefix of t
// containing pointer data. Anything after this offset is scalar data.
// keep in sync with ../cmd/compile/internal/reflectdata/reflect.go
func typeptrdata(t *abi.Type) uintptr {
        switch t.Kind() {
        case abi.Struct:
                st := (*structType)(unsafe.Pointer(t))
                // find the last field that has pointers.
                field := -1
                for i := range st.Fields {
                        ft := st.Fields[i].Typ
                        if ft.Pointers() {
                                field = i
                        }
                }
                if field == -1 {
                        return 0
                }
                f := st.Fields[field]
                return f.Offset + f.Typ.PtrBytes

        default:
                panic("reflect.typeptrdata: unexpected type, " + stringFor(t))
        }
}

// See cmd/compile/internal/reflectdata/reflect.go for derivation of constant.
const maxPtrmaskBytes = 2048

// ArrayOf returns the array type with the given length and element type.
// For example, if t represents int, ArrayOf(5, t) represents [5]int.
//
// If the resulting type would be larger than the available address space,
// ArrayOf panics.
func ArrayOf(length int, elem Type) Type {
        if length < 0 {
                panic("reflect: negative length passed to ArrayOf")
        }

        typ := elem.common()

        // Look in cache.
        ckey := cacheKey{Array, typ, nil, uintptr(length)}
        if array, ok := lookupCache.Load(ckey); ok {
                return array.(Type)
        }

        // Look in known types.
        s := "[" + strconv.Itoa(length) + "]" + stringFor(typ)
        for _, tt := range typesByString(s) {
                array := (*arrayType)(unsafe.Pointer(tt))
                if array.Elem == typ {
                        ti, _ := lookupCache.LoadOrStore(ckey, toRType(tt))
                        return ti.(Type)
                }
        }

        // Make an array type.
        var iarray any = [1]unsafe.Pointer{}
        prototype := *(**arrayType)(unsafe.Pointer(&iarray))
        array := *prototype
        array.TFlag = typ.TFlag & abi.TFlagRegularMemory
        array.Str = resolveReflectName(newName(s, "", false, false))
        array.Hash = fnv1(typ.Hash, '[')
        for n := uint32(length); n > 0; n >>= 8 {
                array.Hash = fnv1(array.Hash, byte(n))
        }
        array.Hash = fnv1(array.Hash, ']')
        array.Elem = typ
        array.PtrToThis = 0
        if typ.Size_ > 0 {
                max := ^uintptr(0) / typ.Size_
                if uintptr(length) > max {
                        panic("reflect.ArrayOf: array size would exceed virtual address space")
                }
        }
        array.Size_ = typ.Size_ * uintptr(length)
        if length > 0 && typ.PtrBytes != 0 {
                array.PtrBytes = typ.Size_*uintptr(length-1) + typ.PtrBytes
        }
        array.Align_ = typ.Align_
        array.FieldAlign_ = typ.FieldAlign_
        array.Len = uintptr(length)
        array.Slice = &(SliceOf(elem).(*rtype).t)

        switch {
        case typ.PtrBytes == 0 || array.Size_ == 0:
                // No pointers.
                array.GCData = nil
                array.PtrBytes = 0

        case length == 1:
                // In memory, 1-element array looks just like the element.
                array.Kind_ |= typ.Kind_ & kindGCProg
                array.GCData = typ.GCData
                array.PtrBytes = typ.PtrBytes

        case typ.Kind_&kindGCProg == 0 && array.Size_ <= maxPtrmaskBytes*8*goarch.PtrSize:
                // Element is small with pointer mask; array is still small.
                // Create direct pointer mask by turning each 1 bit in elem
                // into length 1 bits in larger mask.
                n := (array.PtrBytes/goarch.PtrSize + 7) / 8
                // Runtime needs pointer masks to be a multiple of uintptr in size.
                n = (n + goarch.PtrSize - 1) &^ (goarch.PtrSize - 1)
                mask := make([]byte, n)
                emitGCMask(mask, 0, typ, array.Len)
                array.GCData = &mask[0]

        default:
                // Create program that emits one element
                // and then repeats to make the array.
                prog := []byte{0, 0, 0, 0} // will be length of prog
                prog = appendGCProg(prog, typ)
                // Pad from ptrdata to size.
                elemPtrs := typ.PtrBytes / goarch.PtrSize
                elemWords := typ.Size_ / goarch.PtrSize
                if elemPtrs < elemWords {
                        // Emit literal 0 bit, then repeat as needed.
                        prog = append(prog, 0x01, 0x00)
                        if elemPtrs+1 < elemWords {
                                prog = append(prog, 0x81)
                                prog = appendVarint(prog, elemWords-elemPtrs-1)
                        }
                }
                // Repeat length-1 times.
                if elemWords < 0x80 {
                        prog = append(prog, byte(elemWords|0x80))
                } else {
                        prog = append(prog, 0x80)
                        prog = appendVarint(prog, elemWords)
                }
                prog = appendVarint(prog, uintptr(length)-1)
                prog = append(prog, 0)
                *(*uint32)(unsafe.Pointer(&prog[0])) = uint32(len(prog) - 4)
                array.Kind_ |= kindGCProg
                array.GCData = &prog[0]
                array.PtrBytes = array.Size_ // overestimate but ok; must match program
        }

        etyp := typ
        esize := etyp.Size()

        array.Equal = nil
        if eequal := etyp.Equal; eequal != nil {
                array.Equal = func(p, q unsafe.Pointer) bool {
                        for i := 0; i < length; i++ {
                                pi := arrayAt(p, i, esize, "i < length")
                                qi := arrayAt(q, i, esize, "i < length")
                                if !eequal(pi, qi) {
                                        return false
                                }

                        }
                        return true
                }
        }

        switch {
        case length == 1 && !ifaceIndir(typ):
                // array of 1 direct iface type can be direct
                array.Kind_ |= kindDirectIface
        default:
                array.Kind_ &^= kindDirectIface
        }

        ti, _ := lookupCache.LoadOrStore(ckey, toRType(&array.Type))
        return ti.(Type)
}

func appendVarint(x []byte, v uintptr) []byte {
        for ; v >= 0x80; v >>= 7 {
                x = append(x, byte(v|0x80))
        }
        x = append(x, byte(v))
        return x
}

// toType converts from a *rtype to a Type that can be returned
// to the client of package reflect. In gc, the only concern is that
// a nil *rtype must be replaced by a nil Type, but in gccgo this
// function takes care of ensuring that multiple *rtype for the same
// type are coalesced into a single Type.
func toType(t *abi.Type) Type {
        if t == nil {
                return nil
        }
        return toRType(t)
}

type layoutKey struct {
        ftyp *funcType // function signature
        rcvr *abi.Type // receiver type, or nil if none
}

type layoutType struct {
        t         *abi.Type
        framePool *sync.Pool
        abid      abiDesc
}

var layoutCache sync.Map // map[layoutKey]layoutType

// funcLayout computes a struct type representing the layout of the
// stack-assigned function arguments and return values for the function
// type t.
// If rcvr != nil, rcvr specifies the type of the receiver.
// The returned type exists only for GC, so we only fill out GC relevant info.
// Currently, that's just size and the GC program. We also fill in
// the name for possible debugging use.
func funcLayout(t *funcType, rcvr *abi.Type) (frametype *abi.Type, framePool *sync.Pool, abid abiDesc) {
        if t.Kind() != abi.Func {
                panic("reflect: funcLayout of non-func type " + stringFor(&t.Type))
        }
        if rcvr != nil && rcvr.Kind() == abi.Interface {
                panic("reflect: funcLayout with interface receiver " + stringFor(rcvr))
        }
        k := layoutKey{t, rcvr}
        if lti, ok := layoutCache.Load(k); ok {
                lt := lti.(layoutType)
                return lt.t, lt.framePool, lt.abid
        }

        // Compute the ABI layout.
        abid = newAbiDesc(t, rcvr)

        // build dummy rtype holding gc program
        x := &abi.Type{
                Align_: goarch.PtrSize,
                // Don't add spill space here; it's only necessary in
                // reflectcall's frame, not in the allocated frame.
                // TODO(mknyszek): Remove this comment when register
                // spill space in the frame is no longer required.
                Size_:    align(abid.retOffset+abid.ret.stackBytes, goarch.PtrSize),
                PtrBytes: uintptr(abid.stackPtrs.n) * goarch.PtrSize,
        }
        if abid.stackPtrs.n > 0 {
                x.GCData = &abid.stackPtrs.data[0]
        }

        var s string
        if rcvr != nil {
                s = "methodargs(" + stringFor(rcvr) + ")(" + stringFor(&t.Type) + ")"
        } else {
                s = "funcargs(" + stringFor(&t.Type) + ")"
        }
        x.Str = resolveReflectName(newName(s, "", false, false))

        // cache result for future callers
        framePool = &sync.Pool{New: func() any {
                return unsafe_New(x)
        }}
        lti, _ := layoutCache.LoadOrStore(k, layoutType{
                t:         x,
                framePool: framePool,
                abid:      abid,
        })
        lt := lti.(layoutType)
        return lt.t, lt.framePool, lt.abid
}

// ifaceIndir reports whether t is stored indirectly in an interface value.
func ifaceIndir(t *abi.Type) bool {
        return t.Kind_&kindDirectIface == 0
}

// Note: this type must agree with runtime.bitvector.
type bitVector struct {
        n    uint32 // number of bits
        data []byte
}

// append a bit to the bitmap.
func (bv *bitVector) append(bit uint8) {
        if bv.n%(8*goarch.PtrSize) == 0 {
                // Runtime needs pointer masks to be a multiple of uintptr in size.
                // Since reflect passes bv.data directly to the runtime as a pointer mask,
                // we append a full uintptr of zeros at a time.
                for i := 0; i < goarch.PtrSize; i++ {
                        bv.data = append(bv.data, 0)
                }
        }
        bv.data[bv.n/8] |= bit << (bv.n % 8)
        bv.n++
}

func addTypeBits(bv *bitVector, offset uintptr, t *abi.Type) {
        if t.PtrBytes == 0 {
                return
        }

        switch Kind(t.Kind_ & kindMask) {
        case Chan, Func, Map, Pointer, Slice, String, UnsafePointer:
                // 1 pointer at start of representation
                for bv.n < uint32(offset/uintptr(goarch.PtrSize)) {
                        bv.append(0)
                }
                bv.append(1)

        case Interface:
                // 2 pointers
                for bv.n < uint32(offset/uintptr(goarch.PtrSize)) {
                        bv.append(0)
                }
                bv.append(1)
                bv.append(1)

        case Array:
                // repeat inner type
                tt := (*arrayType)(unsafe.Pointer(t))
                for i := 0; i < int(tt.Len); i++ {
                        addTypeBits(bv, offset+uintptr(i)*tt.Elem.Size_, tt.Elem)
                }

        case Struct:
                // apply fields
                tt := (*structType)(unsafe.Pointer(t))
                for i := range tt.Fields {
                        f := &tt.Fields[i]
                        addTypeBits(bv, offset+f.Offset, f.Typ)
                }
        }
}

// TypeFor returns the [Type] that represents the type argument T.
func TypeFor[T any]() Type {
        return TypeOf((*T)(nil)).Elem()
}