[PATCH RFC v2 02/25] review: do not clear fields a re-adding caller does not know

add_series_to_db()'s UPSERT arm writes pw_series_id and fingerprint
straight from the excluded row, so every re-add clears whatever the
caller did not happen to know.

The callers do not all know both.  The Patchwork tracker re-adds a series
to attach its pw id and has no fingerprint.  rescan_branches() replays a
branch and has neither.  A CLI re-track has the fingerprint and no pw id.
Each one dropped what the others had recorded, leaving a series that no
longer matched by content, or one that lost its Patchwork link.

Passing None means "not known here", not "clear it".  Use COALESCE.

Signed-off-by: Christian Brauner (Amutable) <[email protected]>
---
 src/b4/review/tracking.py | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/b4/review/tracking.py b/src/b4/review/tracking.py
index a0c4ca4f..52b9a897 100644
--- a/src/b4/review/tracking.py
+++ b/src/b4/review/tracking.py
@@ -449,7 +449,15 @@ def add_series_to_db(
     added_at: Optional[str] = None,
     is_rethreaded: bool = False,
 ) -> int:
-    """Add a series to the tracking database. Returns the track_id."""
+    """Add a series to the tracking database. Returns the track_id.
+
+    On conflict the identity fields converge instead of overwriting: a
+    caller that does not know the Patchwork id or the fingerprint leaves
+    an existing one in place.  Re-adds come from callers that never
+    learned those fields -- the Patchwork tracker attaching its id,
+    rescan_branches replaying a branch -- and each used to wipe whatever
+    the others had recorded.
+    """
     if added_at is None:
         added_at = datetime.datetime.now(datetime.timezone.utc).isoformat()
     cursor = conn.execute(
@@ -466,8 +474,8 @@ def add_series_to_db(
             added_at = COALESCE(series.added_at, excluded.added_at),
             message_id = excluded.message_id,
             num_patches = excluded.num_patches,
-            pw_series_id = excluded.pw_series_id,
-            fingerprint = excluded.fingerprint,
+            pw_series_id = COALESCE(excluded.pw_series_id, series.pw_series_id),
+            fingerprint = COALESCE(excluded.fingerprint, series.fingerprint),
             is_rethreaded = excluded.is_rethreaded
         RETURNING track_id
     """,

-- 
2.53.0