slack: distinguish PR merge vs close

"If the action is closed and the merged key is false, the pull
request was closed with unmerged commits. If the action is
closed and the merged key is true, the pull request was merged."

https://docs.github.com/en/[email protected]/developers/webhooks-and-events/webhooks/webhook-events-and-payloads#pull_request

Author: yasunariw

lib/slack.ml

@@ -36,11 +36,11 @@ let pluralize name num suffix = if num = 1 then sprintf "%s" name else String.co
 
 let generate_pull_request_notification notification channel =
   let { action; number; sender; pull_request; repository } = notification in
-  let ({ body; title; html_url; labels; _ } : pull_request) = pull_request in
+  let ({ body; title; html_url; labels; merged; _ } : pull_request) = pull_request in
   let action, body =
     match action with
     | Opened -> "opened", Some body
-    | Closed -> "closed", None
+    | Closed -> (if merged then "merged" else "closed"), None
     | Reopened -> "reopened", None
     | Labeled -> "labeled", show_labels labels
     | _ ->

test/slack_payloads.expected

@@ -286,11 +286,11 @@ will notify #default
   "attachments": [
     {
       "fallback":
-        "<https://github.com/xinyuluo/monorepo|[xinyuluo/monorepo]> Pull request #2 <https://github.com/xinyuluo/monorepo/pull/2|Update README.md> closed by *xinyuluo*",
+        "<https://github.com/xinyuluo/monorepo|[xinyuluo/monorepo]> Pull request #2 <https://github.com/xinyuluo/monorepo/pull/2|Update README.md> merged by *xinyuluo*",
       "mrkdwn_in": [ "text" ],
       "color": "#ccc",
       "pretext":
-        "<https://github.com/xinyuluo/monorepo|[xinyuluo/monorepo]> Pull request #2 <https://github.com/xinyuluo/monorepo/pull/2|Update README.md> closed by *xinyuluo*"
+        "<https://github.com/xinyuluo/monorepo|[xinyuluo/monorepo]> Pull request #2 <https://github.com/xinyuluo/monorepo/pull/2|Update README.md> merged by *xinyuluo*"
     }
   ]
 }