Add merge request popover with details

- Show pipeline status, title, MR Status and project path
- Popover attached to gitlab flavored markdown everywhere, including:
  + MR/Issue Title
  + MR/Issue description
  + MR/Issue comments
  + Rendered markdown files

4 files changed, 196 insertions, 0 deletions

diff --git a/app/assets/javascripts/mr_popover/components/mr_popover.vue b/app/assets/javascripts/mr_popover/components/mr_popover.vue
new file mode 100644
index 00000000000..8e2d8fa816a
--- /dev/null
+++ b/app/assets/javascripts/mr_popover/components/mr_popover.vue
@@ -0,0 +1,110 @@
+<script>
+import { GlPopover, GlSkeletonLoading } from '@gitlab/ui';
+import Icon from '../../vue_shared/components/icon.vue';
+import CiIcon from '../../vue_shared/components/ci_icon.vue';
+import timeagoMixin from '../../vue_shared/mixins/timeago';
+import query from '../queries/merge_request.graphql';
+import { mrStates, humanMRStates } from '../constants';
+
+export default {
+  name: 'MRPopover',
+  components: {
+    GlPopover,
+    GlSkeletonLoading,
+    Icon,
+    CiIcon,
+  },
+  mixins: [timeagoMixin],
+  props: {
+    target: {
+      type: HTMLAnchorElement,
+      required: true,
+    },
+    projectPath: {
+      type: String,
+      required: true,
+    },
+    mergeRequestIID: {
+      type: String,
+      required: true,
+    },
+    mergeRequestTitle: {
+      type: String,
+      required: true,
+    },
+  },
+  data() {
+    return {
+      mergeRequest: {},
+    };
+  },
+  computed: {
+    detailedStatus() {
+      return this.mergeRequest.headPipeline && this.mergeRequest.headPipeline.detailedStatus;
+    },
+    formattedTime() {
+      return this.timeFormated(this.mergeRequest.createdAt);
+    },
+    statusBoxClass() {
+      switch (this.mergeRequest.state) {
+        case mrStates.merged:
+          return 'status-box-mr-merged';
+        case mrStates.closed:
+          return 'status-box-closed';
+        default:
+          return 'status-box-open';
+      }
+    },
+    stateHumanName() {
+      switch (this.mergeRequest.state) {
+        case mrStates.merged:
+          return humanMRStates.merged;
+        case mrStates.closed:
+          return humanMRStates.closed;
+        default:
+          return humanMRStates.open;
+      }
+    },
+    showDetails() {
+      return Object.keys(this.mergeRequest).length > 0;
+    },
+  },
+  apollo: {
+    mergeRequest: {
+      query,
+      update: data => data.project.mergeRequest,
+      variables() {
+        const { projectPath, mergeRequestIID } = this;
+
+        return {
+          projectPath,
+          mergeRequestIID,
+        };
+      },
+    },
+  },
+};
+</script>
+
+<template>
+  <gl-popover :target="target" boundary="viewport" placement="top" show>
+    <div class="mr-popover">
+      <div v-if="$apollo.loading">
+        <gl-skeleton-loading :lines="1" class="animation-container-small mt-1" />
+      </div>
+      <div v-else-if="showDetails" class="d-flex align-items-center justify-content-between">
+        <div class="d-inline-flex align-items-center">
+          <div :class="`issuable-status-box status-box ${statusBoxClass}`">
+            {{ stateHumanName }}
+          </div>
+          <span class="text-secondary">Opened <time v-text="formattedTime"></time></span>
+        </div>
+        <ci-icon v-if="detailedStatus" :status="detailedStatus" />
+      </div>
+      <h5 class="my-2">{{ mergeRequestTitle }}</h5>
+      <div class="text-secondary">
+        {{ `${projectPath}!${mergeRequestIID}` }}
+      </div>
+    </div>
+  </gl-popover>
+</template>
diff --git a/app/assets/javascripts/mr_popover/constants.js b/app/assets/javascripts/mr_popover/constants.js
new file mode 100644
index 00000000000..433df844c80
--- /dev/null
+++ b/app/assets/javascripts/mr_popover/constants.js
@@ -0,0 +1,10 @@
+export const mrStates = {
+  merged: 'merged',
+  closed: 'closed',
+};
+
+export const humanMRStates = {
+  merged: 'Merged',
+  closed: 'Closed',
+  open: 'Open',
+};
diff --git a/app/assets/javascripts/mr_popover/index.js b/app/assets/javascripts/mr_popover/index.js
new file mode 100644
index 00000000000..cc686b401d2
--- /dev/null
+++ b/app/assets/javascripts/mr_popover/index.js
@@ -0,0 +1,62 @@
+import Vue from 'vue';
+import VueApollo from 'vue-apollo';
+import MRPopover from './components/mr_popover.vue';
+import createDefaultClient from '~/lib/graphql';
+
+let renderedPopover;
+let renderFn;
+
+const handleUserPopoverMouseOut = ({ target }) => {
+  target.removeEventListener('mouseleave', handleUserPopoverMouseOut);
+
+  if (renderFn) {
+    clearTimeout(renderFn);
+  }
+  if (renderedPopover) {
+    renderedPopover.$destroy();
+    renderedPopover = null;
+  }
+};
+
+/**
+ * Adds a MergeRequestPopover component to the body, hands over as much data as the target element has in data attributes.
+ * loads based on data-project-path and data-iid more data about an MR from the API and sets it on the popover
+ */
+const handleMRPopoverMount = apolloProvider => ({ target }) => {
+  // Add listener to actually remove it again
+  target.addEventListener('mouseleave', handleUserPopoverMouseOut);
+
+  const { projectPath, mrTitle, iid } = target.dataset;
+  const mergeRequest = {};
+
+  renderFn = setTimeout(() => {
+    const MRPopoverComponent = Vue.extend(MRPopover);
+    renderedPopover = new MRPopoverComponent({
+      propsData: {
+        target,
+        projectPath,
+        mergeRequestIID: iid,
+        mergeRequest,
+        mergeRequestTitle: mrTitle,
+      },
+      apolloProvider,
+    });
+
+    renderedPopover.$mount();
+  }, 200); // 200ms delay so not every mouseover triggers Popover + API Call
+};
+
+export default elements => {
+  const mrLinks = elements || [...document.querySelectorAll('.gfm-merge_request')];
+  if (mrLinks.length > 0) {
+    Vue.use(VueApollo);
+
+    const apolloProvider = new VueApollo({
+      defaultClient: createDefaultClient(),
+    });
+
+    mrLinks.forEach(el => {
+      el.addEventListener('mouseenter', handleMRPopoverMount(apolloProvider));
+    });
+  }
+};
diff --git a/app/assets/javascripts/mr_popover/queries/merge_request.graphql b/app/assets/javascripts/mr_popover/queries/merge_request.graphql
new file mode 100644
index 00000000000..0bb9bc03bc7
--- /dev/null
+++ b/app/assets/javascripts/mr_popover/queries/merge_request.graphql
@@ -0,0 +1,14 @@
+query mergeRequest($projectPath: ID!, $mergeRequestIID: ID!) {
+  project(fullPath: $projectPath) {
+    mergeRequest(iid: $mergeRequestIID) {
+      createdAt
+      state
+      headPipeline {
+        detailedStatus {
+          icon
+          group
+        }
+      }
+    }
+  }
+}