go/types: add go1.23 iterator methods for 10 exported types

These methods will not be mirrored in types2 until the
bootstrap compiler reaches go1.23; therefore range-over-func
statements must not be used in code common to types + types2.

Fixes #66626

Change-Id: I3c2c15e3652ee95d9aff208d8a188b912ed5bc9a
Reviewed-on: https://go-review.googlesource.com/c/go/+/575455
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>

api/next/66626.txt

@@ -0,0 +1,11 @@
+pkg go/types, method (*Interface) EmbeddedTypes() iter.Seq[Type] #66626
+pkg go/types, method (*Interface) ExplicitMethods() iter.Seq[*Func] #66626
+pkg go/types, method (*Interface) Methods() iter.Seq[*Func] #66626
+pkg go/types, method (*MethodSet) Methods() iter.Seq[*Selection] #66626
+pkg go/types, method (*Named) Methods() iter.Seq[*Func] #66626
+pkg go/types, method (*Scope) Children() iter.Seq[*Scope] #66626
+pkg go/types, method (*Struct) Fields() iter.Seq[*Var] #66626
+pkg go/types, method (*Tuple) Variables() iter.Seq[*Var] #66626
+pkg go/types, method (*TypeList) Types() iter.Seq[Type] #66626
+pkg go/types, method (*TypeParamList) TypeParams() iter.Seq[*TypeParam] #66626
+pkg go/types, method (*Union) Terms() iter.Seq[*Term] #66626

doc/next/6-stdlib/99-minor/go/types/66626.md

@@ -0,0 +1,32 @@
+
+All `go/types` data structures that expose sequences using a pair of
+methods such as `Len() int` and `At(int) T` now also methods that
+return iterators, allowing you to simplify code such as this:
+
+```go
+params := fn.Type.(*types.Signature).Params()
+for i := 0; i < params.Len(); i++ {
+   use(params.At(i))
+}
+```
+
+to this:
+
+```go
+for param := range fn.Signature().Params().Variables() {
+   use(param)
+}
+```
+
+The methods are:
+[`Interface.EmbeddedTypes`](/pkg/go/types#Interface.EmbeddedTypes),
+[`Interface.ExplicitMethods`](/pkg/go/types#Interface.ExplicitMethods),
+[`Interface.Methods`](/pkg/go/types#Interface.Methods),
+[`MethodSet.Methods`](/pkg/go/types#MethodSet.Methods),
+[`Named.Methods`](/pkg/go/types#Named.Methods),
+[`Scope.Children`](/pkg/go/types#Scope.Children),
+[`Struct.Fields`](/pkg/go/types#Struct.Fields),
+[`Tuple.Variables`](/pkg/go/types#Tuple.Variables),
+[`TypeList.Types`](/pkg/go/types#TypeList.Types),
+[`TypeParamList.TypeParams`](/pkg/go/types#TypeParamList.TypeParams),
+[`Union.Terms`](/pkg/go/types#Union.Terms).

src/go/types/example_test.go

@@ -136,9 +136,8 @@ type I interface { m() byte }
 	celsius := pkg.Scope().Lookup("Celsius").Type()
 	for _, t := range []types.Type{celsius, types.NewPointer(celsius)} {
 		fmt.Printf("Method set of %s:\n", t)
-		mset := types.NewMethodSet(t)
-		for i := 0; i < mset.Len(); i++ {
-			fmt.Println(mset.At(i))
+		for m := range types.NewMethodSet(t).Methods() {
+			fmt.Println(m)
 		}
 		fmt.Println()
 	}

src/go/types/iter.go

@@ -0,0 +1,159 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import "iter"
+
+// This file defines go1.23 iterator methods for a variety of data
+// types. They are not mirrored to cmd/compile/internal/types2, as
+// there is no point doing so until the bootstrap compiler it at least
+// go1.23; therefore go1.23-style range statements should not be used
+// in code common to types and types2, though clients of go/types are
+// free to use them.
+
+// Methods returns a go1.23 iterator over all the methods of an
+// interface, ordered by Id.
+//
+// Example: for m := range t.Methods() { ... }
+func (t *Interface) Methods() iter.Seq[*Func] {
+	return func(yield func(m *Func) bool) {
+		for i := range t.NumMethods() {
+			if !yield(t.Method(i)) {
+				break
+			}
+		}
+	}
+}
+
+// ExplicitMethods returns a go1.23 iterator over the explicit methods of
+// an interface, ordered by Id.
+//
+// Example: for m := range t.ExplicitMethods() { ... }
+func (t *Interface) ExplicitMethods() iter.Seq[*Func] {
+	return func(yield func(m *Func) bool) {
+		for i := range t.NumExplicitMethods() {
+			if !yield(t.ExplicitMethod(i)) {
+				break
+			}
+		}
+	}
+}
+
+// EmbeddedTypes returns a go1.23 iterator over the types embedded within an interface.
+//
+// Example: for e := range t.EmbeddedTypes() { ... }
+func (t *Interface) EmbeddedTypes() iter.Seq[Type] {
+	return func(yield func(e Type) bool) {
+		for i := range t.NumEmbeddeds() {
+			if !yield(t.EmbeddedType(i)) {
+				break
+			}
+		}
+	}
+}
+
+// Methods returns a go1.23 iterator over the declared methods of a named type.
+//
+// Example: for m := range t.Methods() { ... }
+func (t *Named) Methods() iter.Seq[*Func] {
+	return func(yield func(m *Func) bool) {
+		for i := range t.NumMethods() {
+			if !yield(t.Method(i)) {
+				break
+			}
+		}
+	}
+}
+
+// Children returns a go1.23 iterator over the child scopes nested within scope s.
+//
+// Example: for child := range scope.Children() { ... }
+func (s *Scope) Children() iter.Seq[*Scope] {
+	return func(yield func(child *Scope) bool) {
+		for i := range s.NumChildren() {
+			if !yield(s.Child(i)) {
+				break
+			}
+		}
+	}
+}
+
+// Fields returns a go1.23 iterator over the fields of a struct type.
+//
+// Example: for field := range s.Fields() { ... }
+func (s *Struct) Fields() iter.Seq[*Var] {
+	return func(yield func(field *Var) bool) {
+		for i := range s.NumFields() {
+			if !yield(s.Field(i)) {
+				break
+			}
+		}
+	}
+}
+
+// Variables returns a go1.23 iterator over the variables of a tuple type.
+//
+// Example: for v := range tuple.Variables() { ... }
+func (t *Tuple) Variables() iter.Seq[*Var] {
+	return func(yield func(v *Var) bool) {
+		for i := range t.Len() {
+			if !yield(t.At(i)) {
+				break
+			}
+		}
+	}
+}
+
+// MethodSet returns a go1.23 iterator over the methods of a method set.
+//
+// Example: for method := range s.Methods() { ... }
+func (s *MethodSet) Methods() iter.Seq[*Selection] {
+	return func(yield func(method *Selection) bool) {
+		for i := range s.Len() {
+			if !yield(s.At(i)) {
+				break
+			}
+		}
+	}
+}
+
+// Terms returns a go1.23 iterator over the terms of a union.
+//
+// Example: for term := range union.Terms() { ... }
+func (u *Union) Terms() iter.Seq[*Term] {
+	return func(yield func(term *Term) bool) {
+		for i := range u.Len() {
+			if !yield(u.Term(i)) {
+				break
+			}
+		}
+	}
+}
+
+// TypeParams returns a go1.23 iterator over a list of type parameters.
+//
+// Example: for tparam := range l.TypeParams() { ... }
+func (l *TypeParamList) TypeParams() iter.Seq[*TypeParam] {
+	return func(yield func(tparam *TypeParam) bool) {
+		for i := range l.Len() {
+			if !yield(l.At(i)) {
+				break
+			}
+		}
+	}
+}
+
+// Types returns a go1.23 iterator over the elements of a list of types.
+//
+// Example: for t := range l.Types() { ... }
+func (l *TypeList) Types() iter.Seq[Type] {
+	return func(yield func(t Type) bool) {
+		for i := range l.Len() {
+			if !yield(l.At(i)) {
+				break
+			}
+		}
+	}
+}