Make the bot check contributors before sending greeting

Author: felixmulder

bot/src/dotty/tools/bot/PullRequestService.scala

@@ -103,6 +103,9 @@ trait PullRequestService {
   def reviewUrl(issueNbr: Int): String =
     withGithubSecret(s"$githubUrl/repos/lampepfl/dotty/pulls/$issueNbr/reviews")
 
+  def contributorsUrl: String =
+    withGithubSecret("https://api.github.com/repos/lampepfl/dotty/contributors")
+
   sealed trait CommitStatus {
     def commit: Commit
     def isValid: Boolean
@@ -183,6 +186,13 @@ trait PullRequestService {
       .headOption
   }
 
+  /** Get all contributors from GitHub */
+  def getContributors(implicit client: Client): Task[Set[String]] =
+    for {
+      authors <- client.expect(get(contributorsUrl))(jsonOf[List[Author]])
+      logins  =  authors.map(_.login).flatten
+    } yield logins.toSet
+
   /** Ordered from earliest to latest */
   def getCommits(issueNbr: Int)(implicit httpClient: Client): Task[List[Commit]] = {
     def makeRequest(url: String): Task[List[Commit]] =
@@ -299,10 +309,16 @@ trait PullRequestService {
           setStatus(statuses.last, httpClient)
       }
 
-      // Send positive comment:
-      _    <- sendInitialComment(issue.number, invalidUsers, commits, httpClient)
-      _    <- httpClient.shutdown
-      resp <- Ok("Fresh PR checked")
+      authors  =  commits.map(_.author.login).flatten.toSet
+      contribs <- getContributors
+      _        <- {
+        if (!authors.forall(contribs.contains))
+          sendInitialComment(issue.number, invalidUsers, commits, httpClient)
+        else
+          Task.now(())
+      }
+      _        <- httpClient.shutdown
+      resp     <- Ok("Fresh PR checked")
     } yield resp
 
   }