update-nixpkgs: more notifications

src/update_nixpkgs/update.py

@@ -93,7 +93,8 @@ def rebase_nixpkgs(
     branch_to_rebase: str,
     integration_branch: str,
     last_day_integration_branch: str,
-    force: bool
+    force: bool,
+        matrix_hookshot: MatrixHookshot
 ) -> NixpkgsRebaseResult | None:
     logging.info("Trying to rebase nixpkgs repository.")
     if nixpkgs_repo.is_dirty():
@@ -125,6 +126,18 @@ def rebase_nixpkgs(
             nixpkgs_repo.git.rebase(f"upstream/{branch_to_rebase}")
         except GitCommandError:
             logging.exception("nixpkgs rebase failed")
+            matrix_hookshot.send_notification(f"""\
+update-nixpkgs: ERROR nixpkgs rebase failed for {branch_to_rebase}. Please resolve the conflict manually with the following commands:
+
+```
+cd nixpkgs
+git fetch upstream
+git fetch origin
+git checkout -b {integration_branch} origin/{branch_to_rebase}
+git rebase upstream/{branch_to_rebase}
+git push origin {integration_branch}
+```
+""")
             sys.exit(1)
 
         # Check if there are new commits compared to the last day's integration branch.