chlog: drop a trailing buildN before appending ubuntu1

An Ubuntu upload of a package sitting at X-2build1 produced
X-2build1ubuntu1: the blind append misrepresents the lineage and,
sorting below the proper X-2ubuntu1, could never supersede it. A real
change on top of a rebuild replaces the marker instead, so the
trailing buildN is now stripped before the ubuntu counter is appended
or incremented: X-2build1 becomes X-2ubuntu1, X-2ubuntu1build1
becomes X-2ubuntu2.

src/changelog.rs

@@ -137,7 +137,9 @@ pub async fn generate_entry(
 enum Bump {
     /// Regular upload: increment the trailing number
     Normal,
-    /// Ubuntu upload: `1.0-9` becomes `1.0-9ubuntu1`
+    /// Ubuntu upload: `1.0-9` becomes `1.0-9ubuntu1`; a trailing
+    /// no-change-rebuild marker is dropped first (`1.0-9build1` becomes
+    /// `1.0-9ubuntu1`)
     Ubuntu,
     /// Non-maintainer upload: `1.0-1` becomes `1.0-1.1`, native `1.0`
     /// becomes `1.0+nmu1`
@@ -158,7 +160,7 @@ fn compute_new_version(
     bump: Bump,
 ) -> Result<String, Box<dyn std::error::Error>> {
     match bump {
-        Bump::Ubuntu => increment_suffix(old_version, "ubuntu"),
+        Bump::Ubuntu => increment_suffix(strip_build_suffix(old_version), "ubuntu"),
         Bump::Rebuild => increment_suffix(old_version, "build"),
         Bump::Nmu => {
             if old_version.contains('-') {
@@ -177,6 +179,19 @@ fn compute_new_version(
     }
 }
 
+/// The version an Ubuntu upload is numbered from: a trailing
+/// no-change-rebuild marker is dropped, because a real change on top of a
+/// rebuild replaces the marker rather than appending to it — `X-2build1`
+/// becomes `X-2ubuntu1`, where an appended `X-2build1ubuntu1` would
+/// misrepresent the lineage and sort below `X-2ubuntu1`
+fn strip_build_suffix(version: &str) -> &str {
+    let stem = version.trim_end_matches(|c: char| c.is_ascii_digit());
+    match stem.strip_suffix("build") {
+        Some(base) if stem.len() < version.len() => &version[..base.len()],
+        _ => version,
+    }
+}
+
 /// The version bump a regular ([`EntryKind::Normal`]) upload gets, derived
 /// from the vendor of the target series: Ubuntu series number their uploads
 /// the Ubuntu way (`1.0-1` becomes `1.0-1ubuntu1`), everything else —
@@ -1139,6 +1154,22 @@ mod tests {
             compute_new_version("15.2.0-9ubuntu1", Bump::Ubuntu).unwrap(),
             "15.2.0-9ubuntu2"
         );
+        // Ubuntu upload on top of a rebuild drops the buildN marker:
+        // appending would give 15.2.0-9build1ubuntu1, which sorts below
+        // the proper 15.2.0-9ubuntu1
+        assert_eq!(
+            compute_new_version("15.2.0-9build1", Bump::Ubuntu).unwrap(),
+            "15.2.0-9ubuntu1"
+        );
+        assert_eq!(
+            compute_new_version("15.2.0-9ubuntu1build1", Bump::Ubuntu).unwrap(),
+            "15.2.0-9ubuntu2"
+        );
+        // Native packages
+        assert_eq!(
+            compute_new_version("15.2.0build1", Bump::Ubuntu).unwrap(),
+            "15.2.0ubuntu1"
+        );
 
         // No change rebuild
         assert_eq!(
@@ -1395,6 +1426,38 @@ mod tests {
         assert_eq!(entry.new_version, "1.0-1ubuntu2");
     }
 
+    /// An Ubuntu upload of a package whose changelog carries a rebuild
+    /// version drops the buildN marker: 1.0-1build1 numbers the next entry
+    /// 1.0-1ubuntu1 (1.0-1build1ubuntu1 would sort below 1.0-1ubuntu1).
+    /// Relies on the host distro-info data listing noble (see the
+    /// distro_info tests). The git repo provides the maintainer identity:
+    /// DEBFULLNAME/DEBEMAIL are process-global and other tests mutate them
+    /// in parallel.
+    #[tokio::test]
+    async fn test_generate_entry_ubuntu_series_numbering_after_rebuild() {
+        let temp_dir = TempDir::new().unwrap();
+        let repo_dir = temp_dir.path();
+        setup_repo(repo_dir);
+        let changelog_path = repo_dir.join("debian/changelog");
+        std::fs::create_dir_all(repo_dir.join("debian")).unwrap();
+        std::fs::write(
+            &changelog_path,
+            "mypackage (1.0-1build1) noble; urgency=medium\n\n  * Initial release\n\n -- Maintainer <m@e.com>  Wed, 01 Jan 2020 00:00:00 +0000\n",
+        )
+        .unwrap();
+
+        let entry = generate_entry(
+            "debian/changelog",
+            Some(repo_dir),
+            None,
+            Some("noble"),
+            EntryKind::Normal,
+        )
+        .await
+        .unwrap();
+        assert_eq!(entry.new_version, "1.0-1ubuntu1");
+    }
+
     #[test]
     fn test_get_maintainer_info() {
         let _identity = IDENTITY_LOCK.blocking_lock();