automatically cancel outdated builds

buildbot_nix/__init__.py

@@ -865,6 +865,30 @@ class GerritNixConfigurator(ConfiguratorBase):
 
         )
 
+        def gerritBranchKey(b):
+            ref = b['branch']
+            if not ref.startswith('refs/changes/'):
+                return ref
+            return ref.rsplit('/', 1)[0]
+        config["services"].append(
+            util.OldBuildCanceller(
+                "lix_build_canceller",
+                filters=[
+                    (
+                        [
+                            f"lix/nix-{kind}"
+                            for kind in [ "eval" ] + [
+                                    f"build/{arch}"
+                                    for arch in self.nix_supported_systems + [ "other" ]
+                            ]
+                        ],
+                        util.SourceStampFilter(project_eq=["lix"])
+                     )
+                ],
+                branch_key=gerritBranchKey
+            )
+        )
+
         systemd_secrets = secrets.SecretInAFile(
             dirname=os.environ["CREDENTIALS_DIRECTORY"],
         )