go/types/typeutil/map.go - tools.git - Git at Google

 // Copyright 2014 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 typeutil defines various utilities for types, such as [Map],
 // a hash table that maps [types.Type] to any value.
 package typeutil

 import (
 	"bytes"
 	"fmt"
 	"go/types"
 	"hash/maphash"
 	"unsafe"

 	"golang.org/x/tools/internal/typeparams"
 )

 // Map is a hash-table-based mapping from types (types.Type) to
 // arbitrary values.  The concrete types that implement
 // the Type interface are pointers.  Since they are not canonicalized,
 // == cannot be used to check for equivalence, and thus we cannot
 // simply use a Go map.
 //
 // Just as with map[K]V, a nil *Map is a valid empty map.
 //
 // Read-only map operations ([Map.At], [Map.Len], and so on) may
 // safely be called concurrently.
 //
 // TODO(adonovan): deprecate in favor of https://go.dev/issues/69420
 // and 69559, if the latter proposals for a generic hash-map type and
 // a types.Hash function are accepted.
 type Map struct {
 	table  map[uint32][]entry // maps hash to bucket; entry.key==nil means unused
 	length int                // number of map entries
 }

 // entry is an entry (key/value association) in a hash bucket.
 type entry struct {
 	key   types.Type
 	value any
 }

 // SetHasher has no effect.
 //
 // It is a relic of an optimization that is no longer profitable. Do
 // not use [Hasher], [MakeHasher], or [SetHasher] in new code.
 func (m *Map) SetHasher(Hasher) {}

 // Delete removes the entry with the given key, if any.
 // It returns true if the entry was found.
 func (m *Map) Delete(key types.Type) bool {
 	if m != nil && m.table != nil {
 		hash := hash(key)
 		bucket := m.table[hash]
 		for i, e := range bucket {
 			if e.key != nil && types.Identical(key, e.key) {
 				// We can't compact the bucket as it
 				// would disturb iterators.
 				bucket[i] = entry{}
 				m.length--
 				return true
 			}
 		}
 	}
 	return false
 }

 // At returns the map entry for the given key.
 // The result is nil if the entry is not present.
 func (m *Map) At(key types.Type) any {
 	if m != nil && m.table != nil {
 		for _, e := range m.table[hash(key)] {
 			if e.key != nil && types.Identical(key, e.key) {
 				return e.value
 			}
 		}
 	}
 	return nil
 }

 // Set sets the map entry for key to val,
 // and returns the previous entry, if any.
 func (m *Map) Set(key types.Type, value any) (prev any) {
 	if m.table != nil {
 		hash := hash(key)
 		bucket := m.table[hash]
 		var hole *entry
 		for i, e := range bucket {
 			if e.key == nil {
 				hole = &bucket[i]
 			} else if types.Identical(key, e.key) {
 				prev = e.value
 				bucket[i].value = value
 				return
 			}
 		}

 		if hole != nil {
 			*hole = entry{key, value} // overwrite deleted entry
 		} else {
 			m.table[hash] = append(bucket, entry{key, value})
 		}
 	} else {
 		hash := hash(key)
 		m.table = map[uint32][]entry{hash: {entry{key, value}}}
 	}

 	m.length++
 	return
 }

 // Len returns the number of map entries.
 func (m *Map) Len() int {
 	if m != nil {
 		return m.length
 	}
 	return 0
 }

 // Iterate calls function f on each entry in the map in unspecified order.
 //
 // If f should mutate the map, Iterate provides the same guarantees as
 // Go maps: if f deletes a map entry that Iterate has not yet reached,
 // f will not be invoked for it, but if f inserts a map entry that
 // Iterate has not yet reached, whether or not f will be invoked for
 // it is unspecified.
 func (m *Map) Iterate(f func(key types.Type, value any)) {
 	if m != nil {
 		for _, bucket := range m.table {
 			for _, e := range bucket {
 				if e.key != nil {
 					f(e.key, e.value)
 				}
 			}
 		}
 	}
 }

 // Keys returns a new slice containing the set of map keys.
 // The order is unspecified.
 func (m *Map) Keys() []types.Type {
 	keys := make([]types.Type, 0, m.Len())
 	m.Iterate(func(key types.Type, _ any) {
 		keys = append(keys, key)
 	})
 	return keys
 }

 func (m *Map) toString(values bool) string {
 	if m == nil {
 		return "{}"
 	}
 	var buf bytes.Buffer
 	fmt.Fprint(&buf, "{")
 	sep := ""
 	m.Iterate(func(key types.Type, value any) {
 		fmt.Fprint(&buf, sep)
 		sep = ", "
 		fmt.Fprint(&buf, key)
 		if values {
 			fmt.Fprintf(&buf, ": %q", value)
 		}
 	})
 	fmt.Fprint(&buf, "}")
 	return buf.String()
 }

 // String returns a string representation of the map's entries.
 // Values are printed using fmt.Sprintf("%v", v).
 // Order is unspecified.
 func (m *Map) String() string {
 	return m.toString(true)
 }

 // KeysString returns a string representation of the map's key set.
 // Order is unspecified.
 func (m *Map) KeysString() string {
 	return m.toString(false)
 }

 // -- Hasher --

 // hash returns the hash of type t.
 // TODO(adonovan): replace by types.Hash when Go proposal #69420 is accepted.
 func hash(t types.Type) uint32 {
 	return theHasher.Hash(t)
 }

 // A Hasher provides a [Hasher.Hash] method to map a type to its hash value.
 // Hashers are stateless, and all are equivalent.
 type Hasher struct{}

 var theHasher Hasher

 // MakeHasher returns Hasher{}.
 // Hashers are stateless; all are equivalent.
 func MakeHasher() Hasher { return theHasher }

 // Hash computes a hash value for the given type t such that
 // Identical(t, t') => Hash(t) == Hash(t').
 func (h Hasher) Hash(t types.Type) uint32 {
 	return hasher{inGenericSig: false}.hash(t)
 }

 // hasher holds the state of a single Hash traversal: whether we are
 // inside the signature of a generic function; this is used to
 // optimize [hasher.hashTypeParam].
 type hasher struct{ inGenericSig bool }

 // hashString computes the Fowler–Noll–Vo hash of s.
 func hashString(s string) uint32 {
 	var h uint32
 	for i := 0; i < len(s); i++ {
 		h ^= uint32(s[i])
 		h *= 16777619
 	}
 	return h
 }

 // hash computes the hash of t.
 func (h hasher) hash(t types.Type) uint32 {
 	// See Identical for rationale.
 	switch t := t.(type) {
 	case *types.Basic:
 		return uint32(t.Kind())

 	case *types.Alias:
 		return h.hash(types.Unalias(t))

 	case *types.Array:
 		return 9043 + 2*uint32(t.Len()) + 3*h.hash(t.Elem())

 	case *types.Slice:
 		return 9049 + 2*h.hash(t.Elem())

 	case *types.Struct:
 		var hash uint32 = 9059
 		for i, n := 0, t.NumFields(); i < n; i++ {
 			f := t.Field(i)
 			if f.Anonymous() {
 				hash += 8861
 			}
 			hash += hashString(t.Tag(i))
 			hash += hashString(f.Name()) // (ignore f.Pkg)
 			hash += h.hash(f.Type())
 		}
 		return hash

 	case *types.Pointer:
 		return 9067 + 2*h.hash(t.Elem())

 	case *types.Signature:
 		var hash uint32 = 9091
 		if t.Variadic() {
 			hash *= 8863
 		}

 		tparams := t.TypeParams()
 		if n := tparams.Len(); n > 0 {
 			h.inGenericSig = true // affects constraints, params, and results

 			for i := range n {
 				tparam := tparams.At(i)
 				hash += 7 * h.hash(tparam.Constraint())
 			}
 		}

 		return hash + 3*h.hashTuple(t.Params()) + 5*h.hashTuple(t.Results())

 	case *types.Union:
 		return h.hashUnion(t)

 	case *types.Interface:
 		// Interfaces are identical if they have the same set of methods, with
 		// identical names and types, and they have the same set of type
 		// restrictions. See go/types.identical for more details.
 		var hash uint32 = 9103

 		// Hash methods.
 		for i, n := 0, t.NumMethods(); i < n; i++ {
 			// Method order is not significant.
 			// Ignore m.Pkg().
 			m := t.Method(i)
 			// Use shallow hash on method signature to
 			// avoid anonymous interface cycles.
 			hash += 3*hashString(m.Name()) + 5*h.shallowHash(m.Type())
 		}

 		// Hash type restrictions.
 		terms, err := typeparams.InterfaceTermSet(t)
 		// if err != nil t has invalid type restrictions.
 		if err == nil {
 			hash += h.hashTermSet(terms)
 		}

 		return hash

 	case *types.Map:
 		return 9109 + 2*h.hash(t.Key()) + 3*h.hash(t.Elem())

 	case *types.Chan:
 		return 9127 + 2*uint32(t.Dir()) + 3*h.hash(t.Elem())

 	case *types.Named:
 		hash := h.hashTypeName(t.Obj())
 		targs := t.TypeArgs()
 		for i := 0; i < targs.Len(); i++ {
 			targ := targs.At(i)
 			hash += 2 * h.hash(targ)
 		}
 		return hash

 	case *types.TypeParam:
 		return h.hashTypeParam(t)

 	case *types.Tuple:
 		return h.hashTuple(t)
 	}

 	panic(fmt.Sprintf("%T: %v", t, t))
 }

 func (h hasher) hashTuple(tuple *types.Tuple) uint32 {
 	// See go/types.identicalTypes for rationale.
 	n := tuple.Len()
 	hash := 9137 + 2*uint32(n)
 	for i := range n {
 		hash += 3 * h.hash(tuple.At(i).Type())
 	}
 	return hash
 }

 func (h hasher) hashUnion(t *types.Union) uint32 {
 	// Hash type restrictions.
 	terms, err := typeparams.UnionTermSet(t)
 	// if err != nil t has invalid type restrictions. Fall back on a non-zero
 	// hash.
 	if err != nil {
 		return 9151
 	}
 	return h.hashTermSet(terms)
 }

 func (h hasher) hashTermSet(terms []*types.Term) uint32 {
 	hash := 9157 + 2*uint32(len(terms))
 	for _, term := range terms {
 		// term order is not significant.
 		termHash := h.hash(term.Type())
 		if term.Tilde() {
 			termHash *= 9161
 		}
 		hash += 3 * termHash
 	}
 	return hash
 }

 // hashTypeParam returns the hash of a type parameter.
 func (h hasher) hashTypeParam(t *types.TypeParam) uint32 {
 	// Within the signature of a generic function, TypeParams are
 	// identical if they have the same index and constraint, so we
 	// hash them based on index.
 	//
 	// When we are outside a generic function, free TypeParams are
 	// identical iff they are the same object, so we can use a
 	// more discriminating hash consistent with object identity.
 	// This optimization saves [Map] about 4% when hashing all the
 	// types.Info.Types in the forward closure of net/http.
 	if !h.inGenericSig {
 		// Optimization: outside a generic function signature,
 		// use a more discrimating hash consistent with object identity.
 		return h.hashTypeName(t.Obj())
 	}
 	return 9173 + 3*uint32(t.Index())
 }

 var theSeed = maphash.MakeSeed()

 // hashTypeName hashes the pointer of tname.
 func (hasher) hashTypeName(tname *types.TypeName) uint32 {
 	// Since types.Identical uses == to compare TypeNames,
 	// the Hash function uses maphash.Comparable.
 	// TODO(adonovan): or will, when it becomes available in go1.24.
 	// In the meantime we use the pointer's numeric value.
 	//
 	//   hash := maphash.Comparable(theSeed, tname)
 	//
 	// (Another approach would be to hash the name and package
 	// path, and whether or not it is a package-level typename. It
 	// is rare for a package to define multiple local types with
 	// the same name.)
 	ptr := uintptr(unsafe.Pointer(tname))
 	if unsafe.Sizeof(ptr) == 8 {
 		hash := uint64(ptr)
 		return uint32(hash ^ (hash >> 32))
 	} else {
 		return uint32(ptr)
 	}
 }

 // shallowHash computes a hash of t without looking at any of its
 // element Types, to avoid potential anonymous cycles in the types of
 // interface methods.
 //
 // When an unnamed non-empty interface type appears anywhere among the
 // arguments or results of an interface method, there is a potential
 // for endless recursion. Consider:
 //
 //	type X interface { m() []*interface { X } }
 //
 // The problem is that the Methods of the interface in m's result type
 // include m itself; there is no mention of the named type X that
 // might help us break the cycle.
 // (See comment in go/types.identical, case *Interface, for more.)
 func (h hasher) shallowHash(t types.Type) uint32 {
 	// t is the type of an interface method (Signature),
 	// its params or results (Tuples), or their immediate
 	// elements (mostly Slice, Pointer, Basic, Named),
 	// so there's no need to optimize anything else.
 	switch t := t.(type) {
 	case *types.Alias:
 		return h.shallowHash(types.Unalias(t))

 	case *types.Signature:
 		var hash uint32 = 604171
 		if t.Variadic() {
 			hash *= 971767
 		}
 		// The Signature/Tuple recursion is always finite
 		// and invariably shallow.
 		return hash + 1062599*h.shallowHash(t.Params()) + 1282529*h.shallowHash(t.Results())

 	case *types.Tuple:
 		n := t.Len()
 		hash := 9137 + 2*uint32(n)
 		for i := range n {
 			hash += 53471161 * h.shallowHash(t.At(i).Type())
 		}
 		return hash

 	case *types.Basic:
 		return 45212177 * uint32(t.Kind())

 	case *types.Array:
 		return 1524181 + 2*uint32(t.Len())

 	case *types.Slice:
 		return 2690201

 	case *types.Struct:
 		return 3326489

 	case *types.Pointer:
 		return 4393139

 	case *types.Union:
 		return 562448657

 	case *types.Interface:
 		return 2124679 // no recursion here

 	case *types.Map:
 		return 9109

 	case *types.Chan:
 		return 9127

 	case *types.Named:
 		return h.hashTypeName(t.Obj())

 	case *types.TypeParam:
 		return h.hashTypeParam(t)
 	}
 	panic(fmt.Sprintf("shallowHash: %T: %v", t, t))
 }
	// Copyright 2014 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 typeutil defines various utilities for types, such as [Map],
	// a hash table that maps [types.Type] to any value.
	package typeutil

	import (
	"bytes"
	"fmt"
	"go/types"
	"hash/maphash"
	"unsafe"

	"golang.org/x/tools/internal/typeparams"
	)

	// Map is a hash-table-based mapping from types (types.Type) to
	// arbitrary values. The concrete types that implement
	// the Type interface are pointers. Since they are not canonicalized,
	// == cannot be used to check for equivalence, and thus we cannot
	// simply use a Go map.
	//
	// Just as with map[K]V, a nil *Map is a valid empty map.
	//
	// Read-only map operations ([Map.At], [Map.Len], and so on) may
	// safely be called concurrently.
	//
	// TODO(adonovan): deprecate in favor of https://go.dev/issues/69420
	// and 69559, if the latter proposals for a generic hash-map type and
	// a types.Hash function are accepted.
	type Map struct {
	table map[uint32][]entry // maps hash to bucket; entry.key==nil means unused
	length int // number of map entries
	}

	// entry is an entry (key/value association) in a hash bucket.
	type entry struct {
	key types.Type
	value any
	}

	// SetHasher has no effect.
	//
	// It is a relic of an optimization that is no longer profitable. Do
	// not use [Hasher], [MakeHasher], or [SetHasher] in new code.
	func (m *Map) SetHasher(Hasher) {}

	// Delete removes the entry with the given key, if any.
	// It returns true if the entry was found.
	func (m *Map) Delete(key types.Type) bool {
	if m != nil && m.table != nil {
	hash := hash(key)
	bucket := m.table[hash]
	for i, e := range bucket {
	if e.key != nil && types.Identical(key, e.key) {
	// We can't compact the bucket as it
	// would disturb iterators.
	bucket[i] = entry{}
	m.length--
	return true
	}
	}
	}
	return false
	}

	// At returns the map entry for the given key.
	// The result is nil if the entry is not present.
	func (m *Map) At(key types.Type) any {
	if m != nil && m.table != nil {
	for _, e := range m.table[hash(key)] {
	if e.key != nil && types.Identical(key, e.key) {
	return e.value
	}
	}
	}
	return nil
	}

	// Set sets the map entry for key to val,
	// and returns the previous entry, if any.
	func (m *Map) Set(key types.Type, value any) (prev any) {
	if m.table != nil {
	hash := hash(key)
	bucket := m.table[hash]
	var hole *entry
	for i, e := range bucket {
	if e.key == nil {
	hole = &bucket[i]
	} else if types.Identical(key, e.key) {
	prev = e.value
	bucket[i].value = value
	return
	}
	}

	if hole != nil {
	*hole = entry{key, value} // overwrite deleted entry
	} else {
	m.table[hash] = append(bucket, entry{key, value})
	}
	} else {
	hash := hash(key)
	m.table = map[uint32][]entry{hash: {entry{key, value}}}
	}

	m.length++
	return
	}

	// Len returns the number of map entries.
	func (m *Map) Len() int {
	if m != nil {
	return m.length
	}
	return 0
	}

	// Iterate calls function f on each entry in the map in unspecified order.
	//
	// If f should mutate the map, Iterate provides the same guarantees as
	// Go maps: if f deletes a map entry that Iterate has not yet reached,
	// f will not be invoked for it, but if f inserts a map entry that
	// Iterate has not yet reached, whether or not f will be invoked for
	// it is unspecified.
	func (m *Map) Iterate(f func(key types.Type, value any)) {
	if m != nil {
	for _, bucket := range m.table {
	for _, e := range bucket {
	if e.key != nil {
	f(e.key, e.value)
	}
	}
	}
	}
	}

	// Keys returns a new slice containing the set of map keys.
	// The order is unspecified.
	func (m *Map) Keys() []types.Type {
	keys := make([]types.Type, 0, m.Len())
	m.Iterate(func(key types.Type, _ any) {
	keys = append(keys, key)
	})
	return keys
	}

	func (m *Map) toString(values bool) string {
	if m == nil {
	return "{}"
	}
	var buf bytes.Buffer
	fmt.Fprint(&buf, "{")
	sep := ""
	m.Iterate(func(key types.Type, value any) {
	fmt.Fprint(&buf, sep)
	sep = ", "
	fmt.Fprint(&buf, key)
	if values {
	fmt.Fprintf(&buf, ": %q", value)
	}
	})
	fmt.Fprint(&buf, "}")
	return buf.String()
	}

	// String returns a string representation of the map's entries.
	// Values are printed using fmt.Sprintf("%v", v).
	// Order is unspecified.
	func (m *Map) String() string {
	return m.toString(true)
	}

	// KeysString returns a string representation of the map's key set.
	// Order is unspecified.
	func (m *Map) KeysString() string {
	return m.toString(false)
	}

	// -- Hasher --

	// hash returns the hash of type t.
	// TODO(adonovan): replace by types.Hash when Go proposal #69420 is accepted.
	func hash(t types.Type) uint32 {
	return theHasher.Hash(t)
	}

	// A Hasher provides a [Hasher.Hash] method to map a type to its hash value.
	// Hashers are stateless, and all are equivalent.
	type Hasher struct{}

	var theHasher Hasher

	// MakeHasher returns Hasher{}.
	// Hashers are stateless; all are equivalent.
	func MakeHasher() Hasher { return theHasher }

	// Hash computes a hash value for the given type t such that
	// Identical(t, t') => Hash(t) == Hash(t').
	func (h Hasher) Hash(t types.Type) uint32 {
	return hasher{inGenericSig: false}.hash(t)
	}

	// hasher holds the state of a single Hash traversal: whether we are
	// inside the signature of a generic function; this is used to
	// optimize [hasher.hashTypeParam].
	type hasher struct{ inGenericSig bool }

	// hashString computes the Fowler–Noll–Vo hash of s.
	func hashString(s string) uint32 {
	var h uint32
	for i := 0; i < len(s); i++ {
	h ^= uint32(s[i])
	h *= 16777619
	}
	return h
	}

	// hash computes the hash of t.
	func (h hasher) hash(t types.Type) uint32 {
	// See Identical for rationale.
	switch t := t.(type) {
	case *types.Basic:
	return uint32(t.Kind())

	case *types.Alias:
	return h.hash(types.Unalias(t))

	case *types.Array:
	return 9043 + 2uint32(t.Len()) + 3h.hash(t.Elem())

	case *types.Slice:
	return 9049 + 2*h.hash(t.Elem())

	case *types.Struct:
	var hash uint32 = 9059
	for i, n := 0, t.NumFields(); i < n; i++ {
	f := t.Field(i)
	if f.Anonymous() {
	hash += 8861
	}
	hash += hashString(t.Tag(i))
	hash += hashString(f.Name()) // (ignore f.Pkg)
	hash += h.hash(f.Type())
	}
	return hash

	case *types.Pointer:
	return 9067 + 2*h.hash(t.Elem())

	case *types.Signature:
	var hash uint32 = 9091
	if t.Variadic() {
	hash *= 8863
	}

	tparams := t.TypeParams()
	if n := tparams.Len(); n > 0 {
	h.inGenericSig = true // affects constraints, params, and results

	for i := range n {
	tparam := tparams.At(i)
	hash += 7 * h.hash(tparam.Constraint())
	}
	}

	return hash + 3h.hashTuple(t.Params()) + 5h.hashTuple(t.Results())

	case *types.Union:
	return h.hashUnion(t)

	case *types.Interface:
	// Interfaces are identical if they have the same set of methods, with
	// identical names and types, and they have the same set of type
	// restrictions. See go/types.identical for more details.
	var hash uint32 = 9103

	// Hash methods.
	for i, n := 0, t.NumMethods(); i < n; i++ {
	// Method order is not significant.
	// Ignore m.Pkg().
	m := t.Method(i)
	// Use shallow hash on method signature to
	// avoid anonymous interface cycles.
	hash += 3hashString(m.Name()) + 5h.shallowHash(m.Type())
	}

	// Hash type restrictions.
	terms, err := typeparams.InterfaceTermSet(t)
	// if err != nil t has invalid type restrictions.
	if err == nil {
	hash += h.hashTermSet(terms)
	}

	return hash

	case *types.Map:
	return 9109 + 2h.hash(t.Key()) + 3h.hash(t.Elem())

	case *types.Chan:
	return 9127 + 2uint32(t.Dir()) + 3h.hash(t.Elem())

	case *types.Named:
	hash := h.hashTypeName(t.Obj())
	targs := t.TypeArgs()
	for i := 0; i < targs.Len(); i++ {
	targ := targs.At(i)
	hash += 2 * h.hash(targ)
	}
	return hash

	case *types.TypeParam:
	return h.hashTypeParam(t)

	case *types.Tuple:
	return h.hashTuple(t)
	}

	panic(fmt.Sprintf("%T: %v", t, t))
	}

	func (h hasher) hashTuple(tuple *types.Tuple) uint32 {
	// See go/types.identicalTypes for rationale.
	n := tuple.Len()
	hash := 9137 + 2*uint32(n)
	for i := range n {
	hash += 3 * h.hash(tuple.At(i).Type())
	}
	return hash
	}

	func (h hasher) hashUnion(t *types.Union) uint32 {
	// Hash type restrictions.
	terms, err := typeparams.UnionTermSet(t)
	// if err != nil t has invalid type restrictions. Fall back on a non-zero
	// hash.
	if err != nil {
	return 9151
	}
	return h.hashTermSet(terms)
	}

	func (h hasher) hashTermSet(terms []*types.Term) uint32 {
	hash := 9157 + 2*uint32(len(terms))
	for _, term := range terms {
	// term order is not significant.
	termHash := h.hash(term.Type())
	if term.Tilde() {
	termHash *= 9161
	}
	hash += 3 * termHash
	}
	return hash
	}

	// hashTypeParam returns the hash of a type parameter.
	func (h hasher) hashTypeParam(t *types.TypeParam) uint32 {
	// Within the signature of a generic function, TypeParams are
	// identical if they have the same index and constraint, so we
	// hash them based on index.
	//
	// When we are outside a generic function, free TypeParams are
	// identical iff they are the same object, so we can use a
	// more discriminating hash consistent with object identity.
	// This optimization saves [Map] about 4% when hashing all the
	// types.Info.Types in the forward closure of net/http.
	if !h.inGenericSig {
	// Optimization: outside a generic function signature,
	// use a more discrimating hash consistent with object identity.
	return h.hashTypeName(t.Obj())
	}
	return 9173 + 3*uint32(t.Index())
	}

	var theSeed = maphash.MakeSeed()

	// hashTypeName hashes the pointer of tname.
	func (hasher) hashTypeName(tname *types.TypeName) uint32 {
	// Since types.Identical uses == to compare TypeNames,
	// the Hash function uses maphash.Comparable.
	// TODO(adonovan): or will, when it becomes available in go1.24.
	// In the meantime we use the pointer's numeric value.
	//
	// hash := maphash.Comparable(theSeed, tname)
	//
	// (Another approach would be to hash the name and package
	// path, and whether or not it is a package-level typename. It
	// is rare for a package to define multiple local types with
	// the same name.)
	ptr := uintptr(unsafe.Pointer(tname))
	if unsafe.Sizeof(ptr) == 8 {
	hash := uint64(ptr)
	return uint32(hash ^ (hash >> 32))
	} else {
	return uint32(ptr)
	}
	}

	// shallowHash computes a hash of t without looking at any of its
	// element Types, to avoid potential anonymous cycles in the types of
	// interface methods.
	//
	// When an unnamed non-empty interface type appears anywhere among the
	// arguments or results of an interface method, there is a potential
	// for endless recursion. Consider:
	//
	// type X interface { m() []*interface { X } }
	//
	// The problem is that the Methods of the interface in m's result type
	// include m itself; there is no mention of the named type X that
	// might help us break the cycle.
	// (See comment in go/types.identical, case *Interface, for more.)
	func (h hasher) shallowHash(t types.Type) uint32 {
	// t is the type of an interface method (Signature),
	// its params or results (Tuples), or their immediate
	// elements (mostly Slice, Pointer, Basic, Named),
	// so there's no need to optimize anything else.
	switch t := t.(type) {
	case *types.Alias:
	return h.shallowHash(types.Unalias(t))

	case *types.Signature:
	var hash uint32 = 604171
	if t.Variadic() {
	hash *= 971767
	}
	// The Signature/Tuple recursion is always finite
	// and invariably shallow.
	return hash + 1062599h.shallowHash(t.Params()) + 1282529h.shallowHash(t.Results())

	case *types.Tuple:
	n := t.Len()
	hash := 9137 + 2*uint32(n)
	for i := range n {
	hash += 53471161 * h.shallowHash(t.At(i).Type())
	}
	return hash

	case *types.Basic:
	return 45212177 * uint32(t.Kind())

	case *types.Array:
	return 1524181 + 2*uint32(t.Len())

	case *types.Slice:
	return 2690201

	case *types.Struct:
	return 3326489

	case *types.Pointer:
	return 4393139

	case *types.Union:
	return 562448657

	case *types.Interface:
	return 2124679 // no recursion here

	case *types.Map:
	return 9109

	case *types.Chan:
	return 9127

	case *types.Named:
	return h.hashTypeName(t.Obj())

	case *types.TypeParam:
	return h.hashTypeParam(t)
	}
	panic(fmt.Sprintf("shallowHash: %T: %v", t, t))
	}