rule: use keyword "any" for global filter override

Author: yasunariw

documentation/config_docs.md

@@ -110,7 +110,7 @@ A **label rule** specifies whether or not a Slack channel should be notified, ba
                 "backend/a5",
                 "backend/a4"
             ],
-            "branch_filters": [],
+            "branch_filters": "any",
             "channel": "backend"
         },
         {
@@ -132,13 +132,13 @@ A **prefix rule** specifies whether or not a Slack channel should be notified, b
 Default behavior is to apply each rule regardless of what branch is pushed, and when a rule is matched, show its `distinct` commits only.
 Branch filters limit rule application to selected branches, and shows _all_ commits on match.
 The filters can be declared globally with `filter_main_branch` (see above), or locally per rule with `branch_filters`, where the latter takes precedence.
-To ignore a globally declared filter for a single rule, declare one locally with an empty list, as shown in the example above.
+To ignore a globally declared filter for a single rule, declare one locally with value "any", as shown in the example above.
 
 | value | description | default |
 |-|-|-|
 | `match` | if commit files have any prefix in this list, they should be routed to the channel | all prefixes matched |
 | `ignore` | if commit files have any prefix in this list, they shouldn't be routed to the channel (even if they have any `match` prefixes) | fall back on `match` field behavior |
-| `branch_filters` | consider commits only if pushed ref branch is in this list | fall back on `filter_main_branch` field behavior (see above) |
+| `branch_filters` | consider commits only if pushed ref branch is in this list; set to "any" to ignore `filter_main_branch` for this rule | fall back on `filter_main_branch` field behavior (see above) |
 | `channel` | channel to notify if the rule is matched | required field |
 
 ## Status Options

lib/atd_adapters.ml

@@ -0,0 +1,48 @@
+module List_or_default_field = struct
+  open Atdgen_runtime.Json_adapter
+
+  module type Param = sig
+    (** the name of the field *)
+    val field_name : string
+
+    (** string alias a user can use to denote default value *)
+    val default_alias : string
+
+    (** Yojson representation of default value *)
+    val default_value : Yojson.Safe.t
+  end
+
+  module Make (P : Param) : S = struct
+    open P
+
+    let assoc_replace l k v = List.map (fun x -> if fst x = k then k, v else x) l
+
+    let normalize x =
+      match x with
+      | `Assoc fields ->
+        begin
+          match List.assoc field_name fields with
+          | `String s when String.equal s default_alias -> `Assoc (assoc_replace fields field_name default_value)
+          | _ | (exception Not_found) -> x
+        end
+      | malformed -> malformed
+
+    let restore x =
+      match x with
+      | `Assoc fields ->
+        begin
+          match List.assoc field_name fields with
+          | value when Yojson.Safe.equal value default_value -> `Assoc (assoc_replace fields field_name (`String "any"))
+          | _ | (exception Not_found) -> x
+        end
+      | malformed -> malformed
+  end
+end
+
+module Branch_filters_adapter = List_or_default_field.Make (struct
+  let field_name = "branch_filters"
+
+  let default_alias = "any"
+
+  let default_value = `List []
+end)

lib/rule.atd

@@ -68,7 +68,7 @@ type prefix_rule = {
   ?ignore : string list nullable;
   ?branch_filters : string list nullable;
   channel_name <json name="channel"> : string;
-}
+} <json adapter.ocaml="Atd_adapters.Branch_filters_adapter">
 
 (* A payload matches a label rule with a channel name if absent from the ignore list
    and present in the allow list. Both `allow` and `ignore` are optional. If `allow`

test/monorobot.json

@@ -46,7 +46,7 @@
                     "backend/branch-filter1"
                 ],
                 "channel": "backend1",
-                "branch_filters": []
+                "branch_filters": "any"
             },
             {
                 "match": [