version: reject an empty debian revision

DebianVersion::parse accepted '1.0-' (empty revision after rsplit on
the last hyphen), where dpkg rejects it with 'revision number is
empty'; downstream filename construction produced garbage like
'foo_1.0-.dsc'. Keep the start-digit warning-only semantics of dpkg
(no new check there) and the accepted '1.0--1' split.

src/debian/version.rs

@@ -48,6 +48,12 @@ impl DebianVersion {
             }
         }
         if let Some(rev) = &debian_revision {
+            if rev.is_empty() {
+                // dpkg rejects a trailing hyphen: "bad syntax: revision
+                // number is empty". Native versions (no `-` at all) are
+                // handled above and stay valid.
+                return Err(format!("empty debian revision in '{}'", raw));
+            }
             for c in rev.chars() {
                 if !(c.is_ascii_alphanumeric() || matches!(c, '.' | '+' | '~') || !c.is_ascii()) {
                     return Err(format!(
@@ -329,6 +335,27 @@ mod tests {
         assert!(DebianVersion::parse("1.0~rc1-2").is_ok());
     }
 
+    /// dpkg rejects a trailing `-` ("bad syntax: revision number is
+    /// empty") but accepts `1.0--1`, where the revision is the text after
+    /// the *last* hyphen (upstream `1.0-` + revision `1`).
+    #[test]
+    fn version_empty_revision() {
+        let err = DebianVersion::parse("1.0-").unwrap_err();
+        assert!(err.contains("empty"), "unexpected message: {err}");
+
+        assert!(DebianVersion::parse("1.0-").is_err());
+        // Epoch variants take the same path.
+        assert!(DebianVersion::parse("3:1.0-").is_err());
+        assert!(DebianVersion::parse("1.0-1").is_ok());
+        // Native versions (no revision at all) are still fine.
+        assert!(DebianVersion::parse("1.0").is_ok());
+        assert!(DebianVersion::parse("3:1.0").is_ok());
+
+        let v = DebianVersion::parse("1.0--1").unwrap();
+        assert_eq!(v.upstream, "1.0-");
+        assert_eq!(v.debian_revision.as_deref(), Some("1"));
+    }
+
     fn cmp_sign(a: &DebianVersion, b: &DebianVersion) -> i32 {
         match a.cmp(b) {
             std::cmp::Ordering::Less => -1,