dgit: Enforce a syntax for nominal distros

These appear in various interchange output like tags.  They should be
sane.  They're going to appear in Dgit: too where people will need to
use them.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

1 files changed, 4 insertions, 1 deletions

diff --git a/dgit b/dgit
index 54b0e6f..de7b4de 100755
--- a/dgit
+++ b/dgit
@@ -727,7 +727,10 @@ sub access_basedistro () {
 
 sub access_nomdistro () {
     my $base = access_basedistro();
-    return cfg("dgit-distro.$base.nominal-distro",'RETURN-UNDEF') // $base;
+    my $r = cfg("dgit-distro.$base.nominal-distro",'RETURN-UNDEF') // $base;
+    $r =~ m/^$distro_re$/ or badcfg
+ "bad syntax for (nominal) distro \`$r' (does not match /^$distro_re$/)";
+    return $r;
 }
 
 sub access_quirk () {