Add support for $__range_s (#12883)

Fixes #12882

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

docs/sources/features/datasources/prometheus.md

@@ -78,9 +78,9 @@ For details of *metric names*, *label names* and *label values* are please refer
 
 #### Using interval and range variables
 
-> Support for `$__range` and `$__range_ms` only available from Grafana v5.3
+> Support for `$__range`, `$__range_s` and `$__range_ms` only available from Grafana v5.3
 
-It's possible to use some global built-in variables in query variables; `$__interval`, `$__interval_ms`, `$__range` and `$__range_ms`, see [Global built-in variables](/reference/templating/#global-built-in-variables) for more information. These can be convenient to use in conjunction with the `query_result` function when you need to filter variable queries since
+It's possible to use some global built-in variables in query variables; `$__interval`, `$__interval_ms`, `$__range`, `$__range_s` and `$__range_ms`, see [Global built-in variables](/reference/templating/#global-built-in-variables) for more information. These can be convenient to use in conjunction with the `query_result` function when you need to filter variable queries since
 `label_values` function doesn't support queries.
 
 Make sure to set the variable's `refresh` trigger to be `On Time Range Change` to get the correct instances when changing the time range on the dashboard.
@@ -94,10 +94,10 @@ Query: query_result(topk(5, sum(rate(http_requests_total[$__range])) by (instanc
 Regex: /"([^"]+)"/
 ```
 
-Populate a variable with the instances having a certain state over the time range shown in the dashboard:
+Populate a variable with the instances having a certain state over the time range shown in the dashboard, using the more precise `$__range_s`:
 
 ```
-Query: query_result(max_over_time(<metric>[$__range]) != <state>)
+Query: query_result(max_over_time(<metric>[${__range_s}s]) != <state>)
 Regex:
 ```
 

docs/sources/reference/templating.md

@@ -277,7 +277,7 @@ This variable is only available in the Singlestat panel and can be used in the p
 
 > Only available in Grafana v5.3+
 
-Currently only supported for Prometheus data sources. This variable represents the range for the current dashboard. It is calculated by `to - from`. It has a millisecond representation called `$__range_ms`.
+Currently only supported for Prometheus data sources. This variable represents the range for the current dashboard. It is calculated by `to - from`. It has a millisecond and a second representation called `$__range_ms` and `$__range_s`.
 
 ## Repeating Panels
 

public/app/plugins/datasource/prometheus/datasource.ts

@@ -489,9 +489,11 @@ export class PrometheusDatasource {
   getRangeScopedVars() {
     let range = this.timeSrv.timeRange();
     let msRange = range.to.diff(range.from);
+    let sRange = Math.round(msRange / 1000);
     let regularRange = kbn.secondsToHms(msRange / 1000);
     return {
       __range_ms: { text: msRange, value: msRange },
+      __range_s: { text: sRange, value: sRange },
       __range: { text: regularRange, value: regularRange },
     };
   }

public/app/plugins/datasource/prometheus/specs/datasource.jest.ts

@@ -321,8 +321,10 @@ describe('PrometheusDatasource', () => {
     it('should have the correct range and range_ms', () => {
       let range = ctx.templateSrvMock.replace.mock.calls[0][1].__range;
       let rangeMs = ctx.templateSrvMock.replace.mock.calls[0][1].__range_ms;
+      let rangeS = ctx.templateSrvMock.replace.mock.calls[0][1].__range_s;
       expect(range).toEqual({ text: '21s', value: '21s' });
       expect(rangeMs).toEqual({ text: 21031, value: 21031 });
+      expect(rangeS).toEqual({ text: 21, value: 21 });
     });
 
     it('should pass the default interval value', () => {