[SIP-15] Making client time use UTC as the local time (#8450)

* [fix] Making client time UTC

* Update UPDATING.md

UPDATING.md

@@ -23,6 +23,9 @@ assists people when migrating to a new version.
 
 ## Next Version
 
+* [8450](https://github.com/apache/incubator-superset/pull/8450): The time ranger picker
+now uses UTC for the tooltips and default placeholder timestamps (sans timezone).
+
 * [8370](https://github.com/apache/incubator-superset/pull/8370): Deprecates
   the `HTTP_HEADERS` variable in favor of `DEFAULT_HTTP_HEADERS` and
   `OVERRIDE_HTTP_HEADERS`. To retain the same behavior you should use

superset/assets/src/explore/components/controls/DateFilterControl.jsx

@@ -67,8 +67,15 @@ const COMMON_TIME_FRAMES = [
 const TIME_GRAIN_OPTIONS = ['seconds', 'minutes', 'hours', 'days', 'weeks', 'months', 'years'];
 
 const MOMENT_FORMAT = 'YYYY-MM-DD[T]HH:mm:ss';
-const DEFAULT_SINCE = moment().startOf('day').subtract(7, 'days').format(MOMENT_FORMAT);
-const DEFAULT_UNTIL = moment().startOf('day').format(MOMENT_FORMAT);
+const DEFAULT_SINCE = moment()
+  .utc()
+  .startOf('day')
+  .subtract(7, 'days')
+  .format(MOMENT_FORMAT);
+const DEFAULT_UNTIL = moment()
+  .utc()
+  .startOf('day')
+  .format(MOMENT_FORMAT);
 const SEPARATOR = ' : ';
 const FREEFORM_TOOLTIP = t(
   'Superset supports smart date parsing. Strings like `last sunday` or ' +
@@ -116,8 +123,12 @@ function getStateFromCommonTimeFrame(value) {
     tab: TABS.DEFAULTS,
     type: TYPES.DEFAULTS,
     common: value,
-    since: moment().startOf('day').subtract(1, units).format(MOMENT_FORMAT),
-    until: moment().startOf('day').format(MOMENT_FORMAT),
+    since: moment()
+      .utc()
+      .startOf('day')
+      .subtract(1, units)
+      .format(MOMENT_FORMAT),
+    until: moment().utc().startOf('day').format(MOMENT_FORMAT),
   };
 }
 
@@ -126,13 +137,15 @@ function getStateFromCustomRange(value) {
   let since;
   let until;
   if (rel === RELATIVE_TIME_OPTIONS.LAST) {
-    until = moment().startOf('day').format(MOMENT_FORMAT);
+    until = moment().utc().startOf('day').format(MOMENT_FORMAT);
     since = moment()
+      .utc()
       .startOf('day')
       .subtract(num, grain)
       .format(MOMENT_FORMAT);
   } else {
     until = moment()
+      .utc()
       .startOf('day')
       .add(num, grain)
       .format(MOMENT_FORMAT);

superset/assets/src/explore/controls.jsx

@@ -951,6 +951,14 @@ export const controls = {
     freeForm: true,
     label: t('Time range'),
     default: t('Last week'),
+    description: t(
+      'The time range for the visualization. All relative times, e.g. "Last month", ' +
+      '"Last 7 days", "now", etc. are evaluated on the server using the server\'s ' +
+      'local time (sans timezone). All tooltips and placeholder times are expressed ' +
+      'in UTC (sans timezone). The timestamps are then evaluated by the database ' +
+      'using the engine\'s local timezone. Note one can explicitly set the timezone ' +
+      'per the ISO 8601 format if specifying either the start and/or end time.',
+    ),
   },
 
   max_bubble_size: {