feat: sort library state when writing to state.yaml (#2504)

Fixes #2475

Author: JoeWang1127

internal/librarian/state.go

@@ -24,6 +24,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"github.com/googleapis/librarian/internal/config"
@@ -186,15 +187,23 @@ func findServiceConfigIn(path string) (string, error) {
 }
 
 func saveLibrarianState(repoDir string, state *config.LibrarianState) error {
-	path := filepath.Join(repoDir, config.LibrarianDir, librarianStateFile)
+	sortByLibraryID(state)
+	stateFile := filepath.Join(repoDir, config.LibrarianDir, librarianStateFile)
 	var buffer bytes.Buffer
 	encoder := yaml.NewEncoder(&buffer)
 	encoder.SetIndent(2)
 	err := encoder.Encode(state)
 	if err != nil {
 		return err
 	}
-	return os.WriteFile(path, buffer.Bytes(), 0644)
+	return os.WriteFile(stateFile, buffer.Bytes(), 0644)
+}
+
+// sortByLibraryID sorts config.LibraryState with respect to ID.
+func sortByLibraryID(state *config.LibrarianState) {
+	sort.Slice(state.Libraries, func(i, j int) bool {
+		return state.Libraries[i].ID < state.Libraries[j].ID
+	})
 }
 
 // readLibraryState reads the library state from a container response, if it exists.

internal/librarian/state_test.go

@@ -493,3 +493,56 @@ func TestLoadRepoStateFromGitHub(t *testing.T) {
 		})
 	}
 }
+
+func TestSortByLibraryID(t *testing.T) {
+	t.Parallel()
+	for _, test := range []struct {
+		name  string
+		state *config.LibrarianState
+		want  *config.LibrarianState
+	}{
+		{
+			name: "sort_with_library_id",
+			state: &config.LibrarianState{
+				Image: "test-image",
+				Libraries: []*config.LibraryState{
+					{
+						ID: "b-library",
+					},
+					{
+						ID: "a-library",
+					},
+				},
+			},
+			want: &config.LibrarianState{
+				Image: "test-image",
+				Libraries: []*config.LibraryState{
+					{
+						ID: "a-library",
+					},
+					{
+						ID: "b-library",
+					},
+				},
+			},
+		},
+		{
+			name: "nil_libraries",
+			state: &config.LibrarianState{
+				Image:     "test-image",
+				Libraries: nil,
+			},
+			want: &config.LibrarianState{
+				Image:     "test-image",
+				Libraries: nil,
+			},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			sortByLibraryID(test.state)
+			if diff := cmp.Diff(test.want, test.state); diff != "" {
+				t.Errorf("sortByLibraryID mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}