Add merge pull request method

github4s/src/main/scala/github4s/Decoders.scala

@@ -368,6 +368,14 @@ object Decoders {
     val issue = deriveDecoder[CreatePullRequestIssue]
     data.widen[CreatePullRequest] or issue.widen[CreatePullRequest]
   }
+  implicit val decoderPullRequestMergeMethod: Decoder[PullRequestMergeMethod] =
+    Decoder[String].emap {
+      case PRMergeMethodMerge.value  => PRMergeMethodMerge.asRight
+      case PRMergeMethodRebase.value => PRMergeMethodRebase.asRight
+      case PRMergeMethodSquash.value => PRMergeMethodSquash.asRight
+      case other                     => s"Unknown pull request merge method: $other".asLeft
+    }
+  implicit val decoderPullRequestMergeResponse: Decoder[PullRequestMergeResponse] = deriveDecoder[PullRequestMergeResponse]
   implicit val decoderCreateReferenceRequest: Decoder[CreateReferenceRequest] =
     deriveDecoder[CreateReferenceRequest]
   implicit val decoderDeleteFileRequest: Decoder[DeleteFileRequest] =

github4s/src/main/scala/github4s/Encoders.scala

@@ -42,12 +42,18 @@ object Encoders {
     }
   }
 
+  implicit val encoderPullRequestMergeRequest: Encoder[PullRequestMergeRequest] =
+    deriveEncoder[PullRequestMergeRequest]
+
   implicit val encodePrrStatus: Encoder[PullRequestReviewState] =
     Encoder.encodeString.contramap(_.value)
 
   implicit val encodePrrEvent: Encoder[PullRequestReviewEvent] =
     Encoder.encodeString.contramap(_.value)
 
+  implicit val encodePrMergeMethod: Encoder[PullRequestMergeMethod] =
+    Encoder.encodeString.contramap(_.value)
+
   implicit val encodeEditGistFile: Encoder[EditGistFile] = {
     deriveEncoder[EditGistFile].mapJsonObject(
       _.filter(e => !(e._1.equals("filename") && e._2.isNull))

github4s/src/main/scala/github4s/GHError.scala

@@ -141,6 +141,30 @@ object GHError {
       deriveDecoder[NotFoundError]
   }
 
+  /**
+   * Corresponds to a 405 status code
+   * @param message that was given in the response body
+   */
+  final case class MethodNotAllowed(message: String) extends GHError(message) {
+    override def toString: String = s"MethodNotAllowed($message)"
+  }
+  object MethodNotAllowed {
+    private[github4s] implicit val methodNotAllowedDecoder: Decoder[MethodNotAllowed] =
+      deriveDecoder[MethodNotAllowed]
+  }
+
+  /**
+   * Corresponds to a 409 status code
+   * @param message that was given in the response body
+   */
+  final case class Conflict(message: String) extends GHError(message) {
+    override def toString: String = s"Conflict($message)"
+  }
+  object Conflict {
+    private[github4s] implicit val conflictDecoder: Decoder[Conflict] =
+      deriveDecoder[Conflict]
+  }
+
   sealed trait ErrorCode
   object ErrorCode {
     case object MissingResource       extends ErrorCode

github4s/src/main/scala/github4s/algebras/PullRequests.scala

@@ -104,6 +104,29 @@ trait PullRequests[F[_]] {
       headers: Map[String, String] = Map()
   ): F[GHResponse[PullRequest]]
 
+  /**
+   * Merge a pull request
+   *
+   * @param owner Owner of the repo
+   * @param repo Name of the repo
+   * @param number of the pull request for which we want to merge
+   * @param commitTitle Title for the automatic commit message
+   * @param commitMessage Extra detail to append to automatic commit message
+   * @param sha SHA that pull request head must match to allow merge
+   * @param mergeMethod Merge method to use. Possible values are merge, squash or rebase. Default is merge.
+   * @param headers Optional user headers to include in the request
+   */
+  def mergePullRequest(
+      owner: String,
+      repo: String,
+      number: Long,
+      commitTitle: Option[String] = None,
+      commitMessage: Option[String] = None,
+      sha: Option[String] = None,
+      mergeMethod: Option[PullRequestMergeMethod] = None,
+      headers: Map[String, String] = Map()
+  ): F[GHResponse[PullRequestMergeResponse]]
+
   /**
    * List pull request reviews.
    *

github4s/src/main/scala/github4s/domain/PullRequest.scala

@@ -78,6 +78,15 @@ final case class CreatePullRequestIssue(
     maintainer_can_modify: Option[Boolean] = Some(true)
 ) extends CreatePullRequest
 
+final case class PullRequestMergeRequest(
+    commit_title: Option[String],
+    commit_message: Option[String],
+    sha: Option[String],
+    merge_method: Option[PullRequestMergeMethod]
+)
+
+final case class PullRequestMergeResponse(sha: String, merged: Boolean, message: String)
+
 sealed abstract class PRFilter(val name: String, val value: String)
     extends Product
     with Serializable {
@@ -154,3 +163,9 @@ final case class ReviewersResponse(
 
 final case class BranchUpdateRequest(expected_head_sha: Option[String])
 final case class BranchUpdateResponse(message: String, url: String)
+
+sealed abstract class PullRequestMergeMethod(val value: String) extends Product with Serializable
+
+case object PRMergeMethodMerge  extends PullRequestMergeMethod("merge")
+case object PRMergeMethodSquash extends PullRequestMergeMethod("squash")
+case object PRMergeMethodRebase extends PullRequestMergeMethod("rebase")

github4s/src/main/scala/github4s/http/HttpClient.scala

@@ -208,6 +208,8 @@ object HttpClient {
       case 401 => response.attemptAs[UnauthorizedError].map(_.asLeft)
       case 403 => response.attemptAs[ForbiddenError].map(_.asLeft)
       case 404 => response.attemptAs[GHError](notFoundEntityDecoder).map(_.asLeft)
+      case 405 => response.attemptAs[MethodNotAllowed].map(_.asLeft)
+      case 409 => response.attemptAs[Conflict].map(_.asLeft)
       case 422 => response.attemptAs[UnprocessableEntityError].map(_.asLeft)
       case 423 => response.attemptAs[RateLimitExceededError].map(_.asLeft)
       case _ =>

github4s/src/main/scala/github4s/interpreters/PullRequestsInterpreter.scala

@@ -81,6 +81,30 @@ class PullRequestsInterpreter[F[_]](implicit client: HttpClient[F]) extends Pull
       .post[CreatePullRequest, PullRequest](s"repos/$owner/$repo/pulls", headers, data)
   }
 
+  override def mergePullRequest(
+      owner: String,
+      repo: String,
+      number: Long,
+      commitTitle: Option[String],
+      commitMessage: Option[String],
+      sha: Option[String],
+      mergeMethod: Option[PullRequestMergeMethod],
+      headers: Map[String, String]
+  ) = {
+    val request = PullRequestMergeRequest(
+      commitTitle,
+      commitMessage,
+      sha,
+      mergeMethod
+    )
+    client
+      .put[PullRequestMergeRequest, PullRequestMergeResponse](
+        s"/repos/$owner/$repo/pulls/$number/merge",
+        headers,
+        request
+      )
+  }
+
   override def listReviews(
       owner: String,
       repo: String,