+#---------- tag format handling ----------
+
+sub access_cfg_tagformats () {
+ split /\,/, access_cfg('dgit-tag-format');
+}
+
+sub need_tagformat ($$) {
+ my ($fmt, $why) = @_;
+ fail "need to use tag format $fmt ($why) but also need".
+ " to use tag format $tagformat_want->[0] ($tagformat_want->[1])".
+ " - no way to proceed"
+ if $tagformat_want && $tagformat_want->[0] ne $fmt;
+ $tagformat_want = [$fmt, $why, $tagformat_want->[2] // 0];
+}
+
+sub select_tagformat () {
+ # sets $tagformatfn
+ return if $tagformatfn && !$tagformat_want;
+ die 'bug' if $tagformatfn && $tagformat_want;
+ # ... $tagformat_want assigned after previous select_tagformat
+
+ my (@supported) = access_cfg_tagformats();
+ printdebug "select_tagformat supported @supported\n";
+
+ $tagformat_want //= [ $supported[0], "distro access configuration", 0 ];
+ printdebug "select_tagformat specified @$tagformat_want\n";
+
+ my ($fmt,$why,$override) = @$tagformat_want;
+
+ fail "target distro supports tag formats @supported".
+ " but have to use $fmt ($why)"
+ unless $override
+ or grep { $_ eq $fmt } @supported;
+
+ $tagformat_want = undef;
+ $tagformat = $fmt;
+ $tagformatfn = ${*::}{"debiantag_$fmt"};
+
+ fail "trying to use unknown tag format \`$fmt' ($why) !"
+ unless $tagformatfn;
+}
+