allow multiple labels in project owner rule

Author: yasunariw

documentation/config_docs.md

@@ -251,7 +251,7 @@ You can optionally provide a **status condition** to specify additional requirem
 
 In GitHub, ["code owners"](https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners) are the users/teams whose review is automatically requested when a PR modifying code in a given directory is opened. **Project owners** behave similarly, with two differences.
 
-- Owners are defined _per PR label_, instead of _per directory_ (or directory pattern)
+- Owners are defined _per PR label (or set of labels)_, instead of _per directory_ (or directory pattern)
 - Definitions should be placed in the per-repo Monorobot configuration file, instead of a `CODEOWNERS` file
 
 Draft PR behavior is similar to code owners. From GitHub documentation:
@@ -272,7 +272,7 @@ Note that the owner of the personal access token cannot be a project owner, as G
                 "owners": ["user1", "user2", "org/team1"]
             },
             {
-                "label": "Label 2",
+                "labels": ["Label 2", "Label 3"],  # rule matches if PR has all labels in the list
                 "owners": ["org/team2", "user3"]
             }
         ]

lib/github.ml

@@ -163,7 +163,7 @@ let gh_link_of_string url_str =
   | _ | (exception Re2.Exceptions.Regex_match_failed _) -> None
 
 let get_project_owners (pr : pull_request) ({ rules } : Config_t.project_owners) =
-  List.fold_left pr.labels ~init:[] ~f:(fun acc l -> List.rev_append (Rule.Project_owners.match_rules l ~rules) acc)
+  Rule.Project_owners.match_rules pr.labels rules
   |> List.dedup_and_sort ~compare:String.compare
   |> List.partition_map ~f:(fun reviewer ->
        try

lib/rule.atd

@@ -86,6 +86,7 @@ type label_rule = {
    - teams: "org/team"
 *)
 type project_owners_rule = {
-  label: string;
+  ?label: string option;
+  ~labels <ocaml default="[]">: string list;
   owners: string list;
 }

lib/rule.ml

@@ -127,8 +127,26 @@ module Label = struct
 end
 
 module Project_owners = struct
-  let match_rules (l : Github_t.label) ~rules =
-    match List.find rules ~f:(fun { label; _ } -> String.equal label l.name) with
-    | Some { owners = []; _ } | None -> []
-    | Some { owners; _ } -> owners
+  module SS = Caml.Set.Make (String)
+
+  let match_rules pr_labels rules =
+    match pr_labels with
+    | [] -> []
+    | _ :: _ ->
+      let pr_labels_set = List.map ~f:(fun (l : Github_t.label) -> l.name) pr_labels |> SS.of_list in
+      let do_match { label; labels; owners } =
+        let labels =
+          match labels with
+          | [] -> Option.value_map label ~f:(fun l -> [ l ]) ~default:[]
+          | labels -> labels
+        in
+        match owners with
+        | [] -> false
+        | _ :: _ ->
+        match labels with
+        | [] -> false
+        | [ label ] -> SS.mem label pr_labels_set
+        | labels -> SS.subset (SS.of_list labels) pr_labels_set
+      in
+      List.find ~f:do_match rules |> Option.value_map ~default:[] ~f:(fun l -> l.owners)
 end