distro_info: add UNRELEASED series handling, use it in deb and chlog

src/distro_info.rs

@@ -169,6 +169,16 @@ pub fn supported_dists() -> Vec<String> {
     DATA.dist.keys().cloned().collect()
 }
 
+/// Special changelog distribution marking an entry that has not been
+/// released to any archive series yet
+pub const UNRELEASED: &str = "UNRELEASED";
+
+/// Whether `series` is the special [`UNRELEASED`] distribution rather than
+/// a real archive series
+pub fn is_unreleased(series: &str) -> bool {
+    series == UNRELEASED
+}
+
 /// Get time-ordered list of series information for a distribution, development series first
 pub async fn get_ordered_series(dist: &str) -> Result<Vec<SeriesInformation>, Box<dyn Error>> {
     let dist_data = DATA.dist.get(dist).ok_or_else(|| {
@@ -206,6 +216,24 @@ pub async fn get_ordered_series_name(dist: &str) -> Result<Vec<String>, Box<dyn
     Ok(series.iter().map(|info| info.series.clone()).collect())
 }
 
+/// The series to actually target when the changelog says [`UNRELEASED`]:
+/// the development series of `dist`, i.e. the first entry of
+/// [`get_ordered_series_name`] (which is documented "development series
+/// first"). UNRELEASED work conventionally targets the next release, not
+/// the last stable one. Any other `series` is returned unchanged. Errors
+/// when `dist` is unknown or has no series list.
+pub async fn effective_series(series: &str, dist: &str) -> Result<String, Box<dyn Error>> {
+    if !is_unreleased(series) {
+        return Ok(series.to_string());
+    }
+
+    get_ordered_series_name(dist)
+        .await?
+        .into_iter()
+        .next()
+        .ok_or_else(|| format!("Distribution '{}' has no series to target", dist).into())
+}
+
 /// Get the latest released series for a dist (excluding future releases and special cases like sid)
 pub async fn get_latest_released_series(dist: &str) -> Result<String, Box<dyn Error>> {
     let latest = get_n_latest_released_series(dist, 1).await?;
@@ -523,6 +551,52 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_is_unreleased() {
+        // Matching is exact: UNRELEASED is uppercase by Debian convention
+        assert!(is_unreleased("UNRELEASED"));
+        assert!(!is_unreleased("unreleased"));
+        assert!(!is_unreleased("noble"));
+        assert!(!is_unreleased(""));
+    }
+
+    #[tokio::test]
+    async fn test_effective_series_passthrough() {
+        // A real series is returned unchanged, and the dist is not even
+        // looked up (an unknown dist only matters for UNRELEASED)
+        assert_eq!(effective_series("noble", "ubuntu").await.unwrap(), "noble");
+        assert_eq!(effective_series("sid", "debian").await.unwrap(), "sid");
+        assert_eq!(
+            effective_series("noble", "unknown-distro").await.unwrap(),
+            "noble"
+        );
+    }
+
+    #[tokio::test]
+    async fn test_effective_series_unreleased() {
+        // UNRELEASED resolves to the development series of the dist, i.e.
+        // the first entry of the time-ordered list. On current distro-info
+        // data this is the next Ubuntu release, while Debian's list starts
+        // with 'experimental' (sid comes second), so assert against the
+        // data itself rather than a hardcoded name.
+        for dist in ["ubuntu", "debian"] {
+            let ordered = get_ordered_series_name(dist).await.unwrap();
+            let resolved = effective_series(UNRELEASED, dist).await.unwrap();
+            assert_eq!(resolved, ordered[0]);
+            assert_ne!(resolved, UNRELEASED);
+        }
+    }
+
+    #[tokio::test]
+    async fn test_effective_series_unknown_dist() {
+        // UNRELEASED on an unknown distribution cannot be resolved
+        assert!(
+            effective_series(UNRELEASED, "unknown-distro")
+                .await
+                .is_err()
+        );
+    }
+
     #[tokio::test]
     async fn test_get_debian_series() {
         let series = get_ordered_series_name("debian").await.unwrap();