fix(team): merge team edit --unit into the current unit policy

Gitea replaces a team's whole unit policy on edit, so
`tea team edit 5 --unit repo.wiki=write` revoked code, issue and pull
request access. team edit now merges --unit into the current policy;
--unit-replace keeps the old replacing behavior.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/teams.go

@@ -35,7 +35,7 @@ func (a *application) teamCommand() *cobra.Command {
 	group.AddCommand(list)
 	for _, verb := range []string{"view", "create", "edit", "delete"} {
 		var name, description, permission string
-		var createRepo, allRepos, force bool
+		var createRepo, allRepos, force, replaceUnits bool
 		var units map[string]string
 		command := &cobra.Command{Use: verb + " <id>", Short: titleCase(verb) + " an organization team", Args: argsExact(1)}
 		switch verb {
@@ -49,7 +49,12 @@ func (a *application) teamCommand() *cobra.Command {
 			command.Flags().StringVar(&name, "name", "", "Team name")
 			command.Flags().StringVar(&description, "description", "", "Team description")
 			command.Flags().StringVar(&permission, "permission", "read", "Default access: read, write, admin")
-			command.Flags().StringToStringVar(&units, "unit", nil, "Unit permissions, for example repo.code=write,repo.issues=read (replaces unit policy)")
+			unitUsage := "Unit permissions, for example repo.code=write,repo.issues=read"
+			if verb == "edit" {
+				unitUsage = "Unit permissions to change, for example repo.wiki=write; merged into the current policy"
+				command.Flags().BoolVar(&replaceUnits, "unit-replace", false, "Replace the whole unit policy with --unit; omitted units lose access")
+			}
+			command.Flags().StringToStringVar(&units, "unit", nil, unitUsage)
 			command.Flags().BoolVar(&createRepo, "can-create-repo", false, "Allow creating organization repositories")
 			command.Flags().BoolVar(&allRepos, "all-repositories", false, "Access every organization repository")
 		}
@@ -68,6 +73,9 @@ func (a *application) teamCommand() *cobra.Command {
 				if err := oneOf("permission", permission, "read", "write", "admin"); err != nil {
 					return err
 				}
+				if replaceUnits && !cmd.Flags().Changed("unit") {
+					return clierr.Wrap(clierr.Usage, errors.New("--unit-replace requires --unit"))
+				}
 				if cmd.Flags().Changed("unit") && (len(units) == 0 || permission == "admin") {
 					return clierr.Wrap(clierr.Usage, errors.New("--unit needs a nonempty policy and cannot restrict administrator access"))
 				}
@@ -106,6 +114,7 @@ func (a *application) teamCommand() *cobra.Command {
 				}
 				if cmd.Flags().Changed("unit") {
 					opts.Units = units
+					opts.ReplaceUnits = replaceUnits
 				}
 				if cmd.Flags().Changed("can-create-repo") {
 					opts.CanCreateRepo = &createRepo