Add optional parameter to list merge requests

Add an optional parameter to list merge requests to restrict the
returned merge requests to those that are "opened", "merged" or
"closed". By default all merge requests are returned. Note that
"all" can be given to explicitly request all merge requests.

doc/api/merge_requests.md

 ## List merge requests
 
-Get all merge requests for this project. This function takes pagination parameters
-`page` and `per_page` to restrict the list of merge requests.
+Get all merge requests for this project.
+The `state` parameter can be used to get only merge requests with a
+given state (`opened`, `closed`, or `merged`) or all of them (`all`).
+The pagination parameters `page` and `per_page` can be used to restrict the
+list of merge requests.
 
 ```
 GET /projects/:id/merge_requests
+GET /projects/:id/merge_requests?state=opened
+GET /projects/:id/merge_requests?state=all
 ```
 
 Parameters:
 
 + `id` (required) - The ID of a project
++ `state` (optional) - Return `all` requests or just those that are `merged`, `opened` or `closed`
 
 ```json
 [

lib/api/merge_requests.rb

@@ -19,14 +19,24 @@ module API
       #
       # Parameters:
       #   id (required) - The ID of a project
+      #   state (optional) - Return requests "merged", "opened" or "closed"
       #
       # Example:
       #   GET /projects/:id/merge_requests
+      #   GET /projects/:id/merge_requests?state=opened
+      #   GET /projects/:id/merge_requests?state=closed
       #
       get ":id/merge_requests" do
         authorize! :read_merge_request, user_project
 
-        present paginate(user_project.merge_requests), with: Entities::MergeRequest
+        mrs = case params["state"]
+              when "opened" then user_project.merge_requests.opened
+              when "closed" then user_project.merge_requests.closed
+              when "merged" then user_project.merge_requests.merged
+              else user_project.merge_requests
+        end
+
+        present paginate(mrs), with: Entities::MergeRequest
       end
 
       # Show MR

spec/requests/api/merge_requests_spec.rb

@@ -7,6 +7,8 @@ describe API::API do
   let(:user) { create(:user) }
   let!(:project) {create(:project, creator_id: user.id, namespace: user.namespace) }
   let!(:merge_request) { create(:merge_request, :simple, author: user, assignee: user, source_project: project, target_project: project, title: "Test") }
+  let!(:merge_request_closed) { create(:merge_request, state: "closed", author: user, assignee: user, source_project: project, target_project: project, title: "Closed test") }
+  let!(:merge_request_merged) { create(:merge_request, state: "merged", author: user, assignee: user, source_project: project, target_project: project, title: "Merged test") }
   let!(:note) { create(:note_on_merge_request, author: user, project: project, noteable: merge_request, note: "a comment on a MR") }
   before {
     project.team << [user, :reporters]
@@ -21,12 +23,42 @@ describe API::API do
     end
 
     context "when authenticated" do
-      it "should return an array of merge_requests" do
+      it "should return an array of all merge_requests" do
         get api("/projects/#{project.id}/merge_requests", user)
         response.status.should == 200
         json_response.should be_an Array
+        json_response.length.should == 3
         json_response.first['title'].should == merge_request.title
       end
+      it "should return an array of all merge_requests" do
+        get api("/projects/#{project.id}/merge_requests?state", user)
+        response.status.should == 200
+        json_response.should be_an Array
+        json_response.length.should == 3
+        json_response.first['title'].should == merge_request.title
+      end
+      it "should return an array of open merge_requests" do
+        get api("/projects/#{project.id}/merge_requests?state=opened", user)
+        response.status.should == 200
+        json_response.should be_an Array
+        json_response.length.should == 1
+        json_response.first['title'].should == merge_request.title
+      end
+      it "should return an array of closed merge_requests" do
+        get api("/projects/#{project.id}/merge_requests?state=closed", user)
+        response.status.should == 200
+        json_response.should be_an Array
+        json_response.length.should == 2
+        json_response.first['title'].should == merge_request_closed.title
+        json_response.second['title'].should == merge_request_merged.title
+      end
+      it "should return an array of merged merge_requests" do
+        get api("/projects/#{project.id}/merge_requests?state=merged", user)
+        response.status.should == 200
+        json_response.should be_an Array
+        json_response.length.should == 1
+        json_response.first['title'].should == merge_request_merged.title
+      end
     end
   end