distro_info: match changelog suite names with their series

Debian packages conventionally target 'unstable' in their
debian/changelog distribution field, but the series data (the
distro-info CSVs) only knows codenames: the suite is the alias
'unstable' of the series 'sid', a mapping the debian-distro-info tool
resolves internally without exposing it in its data.

Add a per-dist suite_aliases reference-data key (debian: unstable ->
sid), with two helpers on top: resolve_suite_alias, identifying a
changelog suite name with its series codename and the dist that
codename belongs to, and series_suite_alias, the inverse direction.
The two names identify the same series.

data/distro_info.yml

@@ -28,6 +28,12 @@
 ##                   series (`<series>-updates`, ...). Deliberately not the
 ##                   `pockets` key: that one is the *search order* of pull,
 ##                   where backports must not fold in.
+##   suite_aliases:  the changelog suite names that alias a series
+##                   codename: Debian packages conventionally target
+##                   'unstable' where the series data carries 'sid'.
+##                   Mapped suite name -> series codename; the two
+##                   names identify the same series, and the selector
+##                   offers the aliased entry as '<suite> (<series>)'.
 ##   build_profiles: the vendor's default DEB_BUILD_PROFILES (Ubuntu
 ##                   activates derivative.ubuntu noudeb, Debian none),
 ##                   mirroring what Dpkg::BuildProfiles resolves when the
@@ -47,6 +53,10 @@ dist:
       - updates
       - security
       - proposed-updates
+    # Debian changelogs conventionally target 'unstable'; the series data
+    # knows the same series as 'sid'.
+    suite_aliases:
+      unstable: sid
     sections:
       # Valid Section values for debian/control: the Debian policy section
       # list unioned with the sections observed in the live Ubuntu archive.

src/distro_info.rs

@@ -87,6 +87,11 @@ struct DistData {
     cross_pockets: Vec<String>,
     #[serde(default)]
     build_profiles: Vec<String>,
+    /// Changelog suite names aliasing a distro-info series codename
+    /// ('unstable' for Debian's 'sid'): the two names identify the same
+    /// series ([`series_suite_alias`], [`resolve_suite_alias`])
+    #[serde(default)]
+    suite_aliases: HashMap<String, String>,
     series: SeriesInfo,
 }
 
@@ -413,6 +418,30 @@ pub async fn get_dist_from_series(series: &str) -> Result<String, Box<dyn Error>
     Err(format!("Unknown series: {}", series).into())
 }
 
+/// The changelog suite name that aliases the series codename of `dist`
+/// (Debian's 'unstable' for 'sid'): the two names identify the same
+/// series. `None` when the series carries no suite alias.
+pub fn series_suite_alias(dist: &str, series: &str) -> Option<String> {
+    dist_data(dist)
+        .ok()?
+        .suite_aliases
+        .iter()
+        .find(|(_suite, codename)| codename.as_str() == series)
+        .map(|(suite, _)| suite.clone())
+}
+
+/// Identify a changelog suite name with the distro-info series codename
+/// it aliases (Debian's 'unstable' is 'sid'), and the dist that codename
+/// belongs to. `None` when `suite` is not a known alias of any dist.
+pub fn resolve_suite_alias(suite: &str) -> Option<(String, String)> {
+    for (dist, data) in DATA.dist.iter() {
+        if let Some(codename) = data.suite_aliases.get(suite) {
+            return Some((dist.clone(), codename.clone()));
+        }
+    }
+    None
+}
+
 /// Get the package pockets available for a given distribution, in search order
 ///
 /// The main archive ('') comes first so that a search without an explicit
@@ -1035,6 +1064,41 @@ mod tests {
         assert!(series.contains(&"jammy".to_string()));
     }
 
+    /// Suite aliases identify a changelog suite name with the series
+    /// codename of the same series: Debian's 'unstable' is 'sid'
+    #[test]
+    fn test_suite_aliases() {
+        assert_eq!(
+            resolve_suite_alias("unstable"),
+            Some(("debian".to_string(), "sid".to_string()))
+        );
+        // A series codename or unknown suite is not an alias
+        assert_eq!(resolve_suite_alias("sid"), None);
+        assert_eq!(resolve_suite_alias("noble"), None);
+        assert_eq!(
+            series_suite_alias("debian", "sid"),
+            Some("unstable".to_string())
+        );
+        assert_eq!(series_suite_alias("debian", "trixie"), None);
+        assert_eq!(series_suite_alias("ubuntu", "noble"), None);
+    }
+
+    /// Every suite alias must map to a real series of its dist, or the
+    /// selector would offer a phantom entry
+    #[tokio::test]
+    async fn test_suite_aliases_target_real_series() {
+        for (dist, data) in DATA.dist.iter() {
+            for (suite, codename) in &data.suite_aliases {
+                let series = get_ordered_series_name(dist).await.unwrap_or_default();
+                assert!(
+                    series.contains(codename),
+                    "suite alias '{suite}' of {dist} maps to '{codename}', \
+                     which is not a known series"
+                );
+            }
+        }
+    }
+
     #[tokio::test]
     async fn test_get_dist_from_series() {
         assert_eq!(get_dist_from_series("sid").await.unwrap(), "debian");