feat(gengapic): generate helpers for Go 1.23 iterators

internal/gengapic/auxiliary.go

@@ -79,6 +79,10 @@ func (g *generator) genAuxFile() error {
 	g.commit(filepath.Join(g.opts.outDir, "auxiliary.go"), g.opts.pkgName)
 	g.reset()
 
+	g.genIteratorsGo123()
+	g.commitWithBuildTag(filepath.Join(g.opts.outDir, "auxiliary_go123.go"), g.opts.pkgName, "go1.23")
+	g.reset()
+
 	return nil
 }
 
@@ -123,6 +127,17 @@ func (g *generator) genIterators() error {
 	return nil
 }
 
+// genIteratorsGo123 generates adapters for Go iterators for Go versions 1.23+.
+func (g *generator) genIteratorsGo123() {
+	// Sort iterators to generate by type name to
+	// avoid spurious regenerations created by
+	// non-deterministic map traversal order.
+	iters := sortIteratorMap(g.aux.iters)
+	for _, iter := range iters {
+		g.pagingIterGo123(iter)
+	}
+}
+
 // sortIteratorMap sorts the map of iterator types by iterTypeName.
 func sortIteratorMap(m map[string]*iterType) []*iterType {
 	var iters []*iterType

internal/gengapic/auxiliary_test.go

@@ -444,6 +444,22 @@ func TestGenIterators(t *testing.T) {
 	}
 
 	txtdiff.Diff(t, g.pt.String(), filepath.Join("testdata", "gen_iterators.want"))
+
+	g.reset()
+
+	wantImports = map[pbinfo.ImportSpec]bool{
+		{Path: "iter"}: true,
+		{Path: "github.com/googleapis/gax-go/v2/iterator"}:                       true,
+		{Name: "examplepb", Path: "cloud.google.com/go/example/apiv1/examplepb"}: true,
+	}
+
+	g.genIteratorsGo123()
+
+	if diff := cmp.Diff(g.imports, wantImports); diff != "" {
+		t.Errorf("imports got(-),want(+):\n%s", diff)
+	}
+
+	txtdiff.Diff(t, g.pt.String(), filepath.Join("testdata", "gen_iterators_go123.want"))
 }
 
 func TestSortOperationWrapperMap(t *testing.T) {

internal/gengapic/generator.go

@@ -214,12 +214,19 @@ func (g *generator) printf(s string, a ...interface{}) {
 
 // TODO(chrisdsmith): Add generator_test.go with TestCommit
 
+func (g *generator) commit(fileName, pkgName string) int {
+	return g.commitWithBuildTag(fileName, pkgName, "")
+}
+
 // commit adds header, etc to current pt and returns the line length of the
 // final file output.
-func (g *generator) commit(fileName, pkgName string) int {
+func (g *generator) commitWithBuildTag(fileName, pkgName, buildTag string) int {
 	var header strings.Builder
 	fmt.Fprintf(&header, license.Apache, time.Now().Year())
 	header.WriteString(g.headerComments.String() + "\n")
+	if buildTag != "" {
+		fmt.Fprintf(&header, "//go:build %s\n\n", buildTag)
+	}
 	fmt.Fprintf(&header, "package %s\n\n", pkgName)
 
 	var imps []pbinfo.ImportSpec

internal/gengapic/paging.go

@@ -389,3 +389,20 @@ func (g *generator) pagingIter(pt *iterType) {
 		g.imports[spec] = true
 	}
 }
+
+func (g *generator) pagingIterGo123(pt *iterType) {
+	p := g.printf
+
+	p("// All returns an iterator. If an error is returned by the iterator, the")
+	p("// iterator will stop after that iteration.")
+	p("func (it *%s) All() iter.Seq2[%s, error] {", pt.iterTypeName, pt.elemTypeName)
+	p("  return iterator.RangeAdapter[%s](it.Next)", pt.elemTypeName)
+	p("}")
+	p("")
+
+	g.imports[pbinfo.ImportSpec{Path: "iter"}] = true
+	g.imports[pbinfo.ImportSpec{Path: "github.com/googleapis/gax-go/v2/iterator"}] = true
+	for _, spec := range pt.elemImports {
+		g.imports[spec] = true
+	}
+}

internal/gengapic/testdata/gen_iterators_go123.want

@@ -0,0 +1,6 @@
+// All returns an iterator. If an error is returned by the iterator, the
+// iterator will stop after that iteration.
+func (it *FooIterator) All() iter.Seq2[*examplepb.Foo, error] {
+	return iterator.RangeAdapter[*examplepb.Foo](it.Next)
+}
+