Extended Web IDE API to get MRs for a certain branch in a project

 New `Api.projectMergeRequests` allows:
 - to query for all MRs on a project without specifying `mergeRequestId`
 - to filter the returned MRs using parameters from
 https://bit.ly/2H7We4V

 The new API request is used for fetching information about MRs
 associated with a particular branch in Web IDE to have IdeSidebar
 behave consistently in both scenarios:
 - getting to a branch from and MR (where we already have info about
 relevant MR), or
 - getting to a branch somehow differently directly

For cases where there are several merge requests that the current branch
is associated with, mark the most recent one as 'current'

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/49663

4 files changed, 70 insertions, 11 deletions

diff --git a/app/assets/javascripts/api.js b/app/assets/javascripts/api.js
index 85eb08cc97d..8754c253881 100644
--- a/app/assets/javascripts/api.js
+++ b/app/assets/javascripts/api.js
@@ -12,6 +12,7 @@ const Api = {
   projectsPath: '/api/:version/projects.json',
   projectPath: '/api/:version/projects/:id',
   projectLabelsPath: '/:namespace_path/:project_path/labels',
+  projectMergeRequestsPath: '/api/:version/projects/:id/merge_requests',
   projectMergeRequestPath: '/api/:version/projects/:id/merge_requests/:mrid',
   projectMergeRequestChangesPath: '/api/:version/projects/:id/merge_requests/:mrid/changes',
   projectMergeRequestVersionsPath: '/api/:version/projects/:id/merge_requests/:mrid/versions',
@@ -111,6 +112,22 @@ const Api = {
     return axios.get(url);
   },
 
+  /**
+   * Get all Merge Requests for a project, eventually filtering based on
+   * supplied parameters
+   * @param projectPath
+   * @param params
+   * @returns {Promise}
+   */
+  projectMergeRequests(projectPath, params = {}) {
+    const url = Api.buildUrl(Api.projectMergeRequestsPath).replace(
+      ':id',
+      encodeURIComponent(projectPath),
+    );
+
+    return axios.get(url, { params });
+  },
+
   // Return Merge Request for project
   projectMergeRequest(projectPath, mergeRequestId, params = {}) {
     const url = Api.buildUrl(Api.projectMergeRequestPath)
diff --git a/app/assets/javascripts/ide/services/index.js b/app/assets/javascripts/ide/services/index.js
index 13449592e62..ba33b6826d6 100644
--- a/app/assets/javascripts/ide/services/index.js
+++ b/app/assets/javascripts/ide/services/index.js
@@ -40,6 +40,9 @@ export default {
   getProjectData(namespace, project) {
     return Api.project(`${namespace}/${project}`);
   },
+  getProjectMergeRequests(projectId, params = {}) {
+    return Api.projectMergeRequests(projectId, params);
+  },
   getProjectMergeRequestData(projectId, mergeRequestId, params = {}) {
     return Api.projectMergeRequest(projectId, mergeRequestId, params);
   },
diff --git a/app/assets/javascripts/ide/stores/actions/merge_request.js b/app/assets/javascripts/ide/stores/actions/merge_request.js
index 18c24369996..362ced248a1 100644
--- a/app/assets/javascripts/ide/stores/actions/merge_request.js
+++ b/app/assets/javascripts/ide/stores/actions/merge_request.js
@@ -4,6 +4,38 @@ import service from '../../services';
 import * as types from '../mutation_types';
 import { activityBarViews } from '../../constants';
 
+export const getMergeRequestsForBranch = ({ commit }, { projectId, branchId } = {}) =>
+  service
+    .getProjectMergeRequests(`${projectId}`, {
+      source_branch: branchId,
+      order_by: 'created_at',
+      per_page: 1,
+    })
+    .then(({ data }) => {
+      if (data.length > 0) {
+        const currentMR = data[0];
+
+        commit(types.SET_MERGE_REQUEST, {
+          projectPath: projectId,
+          mergeRequestId: currentMR.iid,
+          mergeRequest: currentMR,
+        });
+
+        commit(types.SET_CURRENT_MERGE_REQUEST, `${currentMR.iid}`);
+      }
+    })
+    .catch(e => {
+      flash(
+        __(`Error fetching merge requests for ${branchId}`),
+        'alert',
+        document,
+        null,
+        false,
+        true,
+      );
+      throw e;
+    });
+
 export const getMergeRequestData = (
   { commit, dispatch, state },
   { projectId, mergeRequestId, targetProjectId = null, force = false } = {},
diff --git a/app/assets/javascripts/ide/stores/actions/project.js b/app/assets/javascripts/ide/stores/actions/project.js
index b65f631c99c..06ed5c0b572 100644
--- a/app/assets/javascripts/ide/stores/actions/project.js
+++ b/app/assets/javascripts/ide/stores/actions/project.js
@@ -136,17 +136,24 @@ export const openBranch = ({ dispatch, state }, { projectId, branchId, basePath
   return dispatch('getFiles', {
     projectId,
     branchId,
-  }).then(() => {
-    if (basePath) {
-      const path = basePath.slice(-1) === '/' ? basePath.slice(0, -1) : basePath;
-      const treeEntryKey = Object.keys(state.entries).find(
-        key => key === path && !state.entries[key].pending,
-      );
-      const treeEntry = state.entries[treeEntryKey];
+  })
+    .then(() => {
+      if (basePath) {
+        const path = basePath.slice(-1) === '/' ? basePath.slice(0, -1) : basePath;
+        const treeEntryKey = Object.keys(state.entries).find(
+          key => key === path && !state.entries[key].pending,
+        );
+        const treeEntry = state.entries[treeEntryKey];
 
-      if (treeEntry) {
-        dispatch('handleTreeEntryAction', treeEntry);
+        if (treeEntry) {
+          dispatch('handleTreeEntryAction', treeEntry);
+        }
       }
-    }
-  });
+    })
+    .then(() => {
+      dispatch('getMergeRequestsForBranch', {
+        projectId,
+        branchId,
+      });
+    });
 };