Explore: jump to explore from panels with mixed datasources

- extends handlers for panel menu and keypress 'x'
- in a mixed-datasource panel finds first datasource that supports
  explore and collects its targets
- passes those targets to the found datasource to be serialized for
  explore state
- removed `supportMetrics` and `supportsExplore`
- use datasource metadata instead (set in plugin.json)
- Use angular timeout to wrap url change for explore jump
- Extract getExploreUrl into core/utils/explore

public/app/features/panel/metrics_panel_ctrl.ts

@@ -6,7 +6,7 @@ import kbn from 'app/core/utils/kbn';
 import { PanelCtrl } from 'app/features/panel/panel_ctrl';
 import * as rangeUtil from 'app/core/utils/rangeutil';
 import * as dateMath from 'app/core/utils/datemath';
-import { renderUrl } from 'app/core/utils/url';
+import { getExploreUrl } from 'app/core/utils/explore';
 
 import { metricsTabDirective } from './metrics_tab';
 
@@ -314,7 +314,12 @@ class MetricsPanelCtrl extends PanelCtrl {
 
   getAdditionalMenuItems() {
     const items = [];
-    if (config.exploreEnabled && this.contextSrv.isEditor && this.datasource && this.datasource.supportsExplore) {
+    if (
+      config.exploreEnabled &&
+      this.contextSrv.isEditor &&
+      this.datasource &&
+      (this.datasource.meta.explore || this.datasource.meta.id === 'mixed')
+    ) {
       items.push({
         text: 'Explore',
         click: 'ctrl.explore();',
@@ -325,14 +330,11 @@ class MetricsPanelCtrl extends PanelCtrl {
     return items;
   }
 
-  explore() {
-    const range = this.timeSrv.timeRangeForUrl();
-    const state = {
-      ...this.datasource.getExploreState(this.panel),
-      range,
-    };
-    const exploreState = JSON.stringify(state);
-    this.$location.url(renderUrl('/explore', { state: exploreState }));
+  async explore() {
+    const url = await getExploreUrl(this.panel, this.panel.targets, this.datasource, this.datasourceSrv, this.timeSrv);
+    if (url) {
+      this.$timeout(() => this.$location.url(url));
+    }
   }
 
   addQuery(target) {

public/app/features/panel/specs/metrics_panel_ctrl.test.ts

@@ -38,7 +38,7 @@ describe('MetricsPanelCtrl', () => {
     describe('and has datasource set that supports explore and user has powers', () => {
       beforeEach(() => {
         ctrl.contextSrv = { isEditor: true };
-        ctrl.datasource = { supportsExplore: true };
+        ctrl.datasource = { meta: { explore: true } };
         additionalItems = ctrl.getAdditionalMenuItems();
       });