bundle x/tools/go/types/typeutil.hash and modify it

See the two "NOTE" comments below. In summary:

* struct field tags are not hashed
* named types are hashed by name rather than by pointer

We are keeping an eye on https://go.dev/issue/69420 as well.

bundled_typeparams.go

@@ -0,0 +1,354 @@
+// Originally bundled from golang.org/x/tools/internal/typeparams@v0.29.0,
+// as it is used by x/tools/go/types/typeutil and is an internal package.
+
+package main
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"go/types"
+)
+
+var errEmptyTypeSet = errors.New("empty type set")
+
+// InterfaceTermSet computes the normalized terms for a constraint interface,
+// returning an error if the term set cannot be computed or is empty. In the
+// latter case, the error will be ErrEmptyTypeSet.
+//
+// See the documentation of StructuralTerms for more information on
+// normalization.
+func typeparams_InterfaceTermSet(iface *types.Interface) ([]*types.Term, error) {
+	return typeparams_computeTermSet(iface)
+}
+
+// UnionTermSet computes the normalized terms for a union, returning an error
+// if the term set cannot be computed or is empty. In the latter case, the
+// error will be ErrEmptyTypeSet.
+//
+// See the documentation of StructuralTerms for more information on
+// normalization.
+func typeparams_UnionTermSet(union *types.Union) ([]*types.Term, error) {
+	return typeparams_computeTermSet(union)
+}
+
+func typeparams_computeTermSet(typ types.Type) ([]*types.Term, error) {
+	tset, err := typeparams_computeTermSetInternal(typ, make(map[types.Type]*typeparams_termSet), 0)
+	if err != nil {
+		return nil, err
+	}
+	if tset.terms.isEmpty() {
+		return nil, errEmptyTypeSet
+	}
+	if tset.terms.isAll() {
+		return nil, nil
+	}
+	var terms []*types.Term
+	for _, term := range tset.terms {
+		terms = append(terms, types.NewTerm(term.tilde, term.typ))
+	}
+	return terms, nil
+}
+
+// A termSet holds the normalized set of terms for a given type.
+//
+// The name termSet is intentionally distinct from 'type set': a type set is
+// all types that implement a type (and includes method restrictions), whereas
+// a term set just represents the structural restrictions on a type.
+type typeparams_termSet struct {
+	complete bool
+	terms    typeparams_termlist
+}
+
+func typeparams_computeTermSetInternal(t types.Type, seen map[types.Type]*typeparams_termSet, depth int) (res *typeparams_termSet, err error) {
+	if t == nil {
+		panic("nil type")
+	}
+
+	const maxTermCount = 100
+	if tset, ok := seen[t]; ok {
+		if !tset.complete {
+			return nil, fmt.Errorf("cycle detected in the declaration of %s", t)
+		}
+		return tset, nil
+	}
+
+	// Mark the current type as seen to avoid infinite recursion.
+	tset := new(typeparams_termSet)
+	defer func() {
+		tset.complete = true
+	}()
+	seen[t] = tset
+
+	switch u := t.Underlying().(type) {
+	case *types.Interface:
+		// The term set of an interface is the intersection of the term sets of its
+		// embedded types.
+		tset.terms = typeparams_allTermlist
+		for i := 0; i < u.NumEmbeddeds(); i++ {
+			embedded := u.EmbeddedType(i)
+			if _, ok := embedded.Underlying().(*types.TypeParam); ok {
+				return nil, fmt.Errorf("invalid embedded type %T", embedded)
+			}
+			tset2, err := typeparams_computeTermSetInternal(embedded, seen, depth+1)
+			if err != nil {
+				return nil, err
+			}
+			tset.terms = tset.terms.intersect(tset2.terms)
+		}
+	case *types.Union:
+		// The term set of a union is the union of term sets of its terms.
+		tset.terms = nil
+		for i := 0; i < u.Len(); i++ {
+			t := u.Term(i)
+			var terms typeparams_termlist
+			switch t.Type().Underlying().(type) {
+			case *types.Interface:
+				tset2, err := typeparams_computeTermSetInternal(t.Type(), seen, depth+1)
+				if err != nil {
+					return nil, err
+				}
+				terms = tset2.terms
+			case *types.TypeParam, *types.Union:
+				// A stand-alone type parameter or union is not permitted as union
+				// term.
+				return nil, fmt.Errorf("invalid union term %T", t)
+			default:
+				if t.Type() == types.Typ[types.Invalid] {
+					continue
+				}
+				terms = typeparams_termlist{{t.Tilde(), t.Type()}}
+			}
+			tset.terms = tset.terms.union(terms)
+			if len(tset.terms) > maxTermCount {
+				return nil, fmt.Errorf("exceeded max term count %d", maxTermCount)
+			}
+		}
+	case *types.TypeParam:
+		panic("unreachable")
+	default:
+		// For all other types, the term set is just a single non-tilde term
+		// holding the type itself.
+		if u != types.Typ[types.Invalid] {
+			tset.terms = typeparams_termlist{{false, t}}
+		}
+	}
+	return tset, nil
+}
+
+// under is a facade for the go/types internal function of the same name. It is
+// used by typeterm.go.
+func typeparams_under(t types.Type) types.Type {
+	return t.Underlying()
+}
+
+// A termlist represents the type set represented by the union
+// t1 ∪ y2 ∪ ... tn of the type sets of the terms t1 to tn.
+// A termlist is in normal form if all terms are disjoint.
+// termlist operations don't require the operands to be in
+// normal form.
+type typeparams_termlist []*typeparams_term
+
+// allTermlist represents the set of all types.
+// It is in normal form.
+
+// allTermlist represents the set of all types.
+// It is in normal form.
+var typeparams_allTermlist = typeparams_termlist{new(typeparams_term)}
+
+// String prints the termlist exactly (without normalization).
+func (xl typeparams_termlist) String() string {
+	if len(xl) == 0 {
+		return "∅"
+	}
+	var buf bytes.Buffer
+	for i, x := range xl {
+		if i > 0 {
+			buf.WriteString(" | ")
+		}
+		buf.WriteString(x.String())
+	}
+	return buf.String()
+}
+
+// isEmpty reports whether the termlist xl represents the empty set of types.
+func (xl typeparams_termlist) isEmpty() bool {
+	// If there's a non-nil term, the entire list is not empty.
+	// If the termlist is in normal form, this requires at most
+	// one iteration.
+	for _, x := range xl {
+		if x != nil {
+			return false
+		}
+	}
+	return true
+}
+
+// isAll reports whether the termlist xl represents the set of all types.
+func (xl typeparams_termlist) isAll() bool {
+	// If there's a 𝓤 term, the entire list is 𝓤.
+	// If the termlist is in normal form, this requires at most
+	// one iteration.
+	for _, x := range xl {
+		if x != nil && x.typ == nil {
+			return true
+		}
+	}
+	return false
+}
+
+// norm returns the normal form of xl.
+func (xl typeparams_termlist) norm() typeparams_termlist {
+	// Quadratic algorithm, but good enough for now.
+	// TODO(gri) fix asymptotic performance
+	used := make([]bool, len(xl))
+	var rl typeparams_termlist
+	for i, xi := range xl {
+		if xi == nil || used[i] {
+			continue
+		}
+		for j := i + 1; j < len(xl); j++ {
+			xj := xl[j]
+			if xj == nil || used[j] {
+				continue
+			}
+			if u1, u2 := xi.union(xj); u2 == nil {
+				// If we encounter a 𝓤 term, the entire list is 𝓤.
+				// Exit early.
+				// (Note that this is not just an optimization;
+				// if we continue, we may end up with a 𝓤 term
+				// and other terms and the result would not be
+				// in normal form.)
+				if u1.typ == nil {
+					return typeparams_allTermlist
+				}
+				xi = u1
+				used[j] = true // xj is now unioned into xi - ignore it in future iterations
+			}
+		}
+		rl = append(rl, xi)
+	}
+	return rl
+}
+
+// union returns the union xl ∪ yl.
+func (xl typeparams_termlist) union(yl typeparams_termlist) typeparams_termlist {
+	return append(xl, yl...).norm()
+}
+
+// intersect returns the intersection xl ∩ yl.
+func (xl typeparams_termlist) intersect(yl typeparams_termlist) typeparams_termlist {
+	if xl.isEmpty() || yl.isEmpty() {
+		return nil
+	}
+
+	// Quadratic algorithm, but good enough for now.
+	// TODO(gri) fix asymptotic performance
+	var rl typeparams_termlist
+	for _, x := range xl {
+		for _, y := range yl {
+			if r := x.intersect(y); r != nil {
+				rl = append(rl, r)
+			}
+		}
+	}
+	return rl.norm()
+}
+
+// A term describes elementary type sets:
+//
+//	 ∅:  (*term)(nil)     == ∅                      // set of no types (empty set)
+//	 𝓤:  &term{}          == 𝓤                      // set of all types (𝓤niverse)
+//	 T:  &term{false, T}  == {T}                    // set of type T
+//	~t:  &term{true, t}   == {t' | under(t') == t}  // set of types with underlying type t
+type typeparams_term struct {
+	tilde bool // valid if typ != nil
+	typ   types.Type
+}
+
+func (x *typeparams_term) String() string {
+	switch {
+	case x == nil:
+		return "∅"
+	case x.typ == nil:
+		return "𝓤"
+	case x.tilde:
+		return "~" + x.typ.String()
+	default:
+		return x.typ.String()
+	}
+}
+
+// union returns the union x ∪ y: zero, one, or two non-nil terms.
+func (x *typeparams_term) union(y *typeparams_term) (_, _ *typeparams_term) {
+	// easy cases
+	switch {
+	case x == nil && y == nil:
+		return nil, nil // ∅ ∪ ∅ == ∅
+	case x == nil:
+		return y, nil // ∅ ∪ y == y
+	case y == nil:
+		return x, nil // x ∪ ∅ == x
+	case x.typ == nil:
+		return x, nil // 𝓤 ∪ y == 𝓤
+	case y.typ == nil:
+		return y, nil // x ∪ 𝓤 == 𝓤
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return x, y // x ∪ y == (x, y) if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ∪ ~t == ~t
+	// ~t ∪  T == ~t
+	//  T ∪ ~t == ~t
+	//  T ∪  T ==  T
+	if x.tilde || !y.tilde {
+		return x, nil
+	}
+	return y, nil
+}
+
+// intersect returns the intersection x ∩ y.
+func (x *typeparams_term) intersect(y *typeparams_term) *typeparams_term {
+	// easy cases
+	switch {
+	case x == nil || y == nil:
+		return nil // ∅ ∩ y == ∅ and ∩ ∅ == ∅
+	case x.typ == nil:
+		return y // 𝓤 ∩ y == y
+	case y.typ == nil:
+		return x // x ∩ 𝓤 == x
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return nil // x ∩ y == ∅ if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ∩ ~t == ~t
+	// ~t ∩  T ==  T
+	//  T ∩ ~t ==  T
+	//  T ∩  T ==  T
+	if !x.tilde || y.tilde {
+		return x
+	}
+	return y
+}
+
+// disjoint reports whether x ∩ y == ∅.
+// x.typ and y.typ must not be nil.
+func (x *typeparams_term) disjoint(y *typeparams_term) bool {
+	ux := x.typ
+	if y.tilde {
+		ux = typeparams_under(ux)
+	}
+	uy := y.typ
+	if x.tilde {
+		uy = typeparams_under(uy)
+	}
+	return !types.Identical(ux, uy)
+}

bundled_typeutil.go

@@ -0,0 +1,295 @@
+// Originally bundled from golang.org/x/tools/go/types/typeutil@v0.29.0.
+// Edited to just keep the hasher API in place, removing the use of internal/typeparams,
+// and removed the inclusion of struct field tags in the hasher.
+
+package main
+
+import (
+	"fmt"
+	"go/types"
+)
+
+// -- Hasher --
+
+// hash returns the hash of type t.
+// TODO(adonovan): replace by types.Hash when Go proposal #69420 is accepted.
+func typeutil_hash(t types.Type) uint32 {
+	return typeutil_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 typeutil_Hasher struct{}
+
+var typeutil_theHasher typeutil_Hasher
+
+// Hash computes a hash value for the given type t such that
+// Identical(t, t') => Hash(t) == Hash(t').
+func (h typeutil_Hasher) Hash(t types.Type) uint32 {
+	return typeutil_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 typeutil_hasher struct{ inGenericSig bool }
+
+// hashString computes the Fowler–Noll–Vo hash of s.
+func typeutil_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 typeutil_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
+			}
+			// NOTE: we must not hash struct field tags, as they do not affect type identity.
+			// hash += typeutil_hashString(t.Tag(i))
+			hash += typeutil_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()
+		for i := range tparams.Len() {
+			h.inGenericSig = true
+			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*typeutil_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 typeutil_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 typeutil_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 typeutil_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 typeutil_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())
+}
+
+// hashTypeName hashes the pointer of tname.
+func (typeutil_hasher) hashTypeName(tname *types.TypeName) uint32 {
+	// NOTE: we must not hash any pointers, as garble is a toolexec tool
+	// so by nature it uses multiple processes.
+	return typeutil_hashString(tname.Name())
+	// 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.)
+	// hash := uintptr(unsafe.Pointer(tname))
+	// return uint32(hash ^ (hash >> 32))
+}
+
+// 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 typeutil_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))
+}