PromQL: Promote negative offset and @ modifer to stable

Following the argument that breaking the invariant that PromQL does
not look ahead of the evaluation time implies a breaking change, we
still need to keep the feature flag around, but at least we can
communicate that the feature is considered stable, and that the
feature flags will be ignored from v3 on.

Signed-off-by: beorn7 <beorn@grafana.com>

cmd/prometheus/main.go

@@ -168,10 +168,10 @@ func (c *flagConfig) setFeatureListOptions(logger log.Logger) error {
 			switch o {
 			case "promql-at-modifier":
 				c.enablePromQLAtModifier = true
-				level.Info(logger).Log("msg", "Experimental promql-at-modifier enabled")
+				level.Info(logger).Log("msg", "promql-at-modifier enabled")
 			case "promql-negative-offset":
 				c.enablePromQLNegativeOffset = true
-				level.Info(logger).Log("msg", "Experimental promql-negative-offset enabled")
+				level.Info(logger).Log("msg", "promql-negative-offset enabled")
 			case "remote-write-receiver":
 				c.web.RemoteWriteReceiver = true
 				level.Info(logger).Log("msg", "Experimental remote-write-receiver enabled")

docs/feature_flags.md

@@ -18,6 +18,11 @@ They may be enabled by default in future versions.
 The `@` modifier lets you specify the evaluation time for instant vector selectors,
 range vector selectors, and subqueries. More details can be found [here](querying/basics.md#modifier).
 
+This feature is considered stable, but since it breaks the invariant that
+PromQL does not look ahead of the evaluation time, it still needs to be enabled
+via this feature flag. The feature will be permanently enabled (and the feature
+flag ignored) upon major release v3.
+
 ## Expand environment variables in external labels
 
 `--enable-feature=expand-external-labels`
@@ -40,6 +45,11 @@ with more recent data.
 
 More details can be found [here](querying/basics.md#offset-modifier).
 
+This feature is considered stable, but since it breaks the invariant that
+PromQL does not look ahead of the evaluation time, it still needs to be enabled
+via this feature flag. The feature will be permanently enabled (and the feature
+flag ignored) upon major release v3.
+
 ## Remote Write Receiver
 
 `--enable-feature=remote-write-receiver`