Alerting: Add MissingSeriesEvalsToResolve to the APIs (#102150)

What is this feature?

A follow-up for #101184, adds AlertRule.MissingSeriesEvalsToResolve to the APIs.

missing_series_evals_to_resolve must be specified too and it must be > 0.

POST /api/ruler/grafana/api/v1/rules/{folderUID} works in the following way:

    If missing_series_evals_to_resolve is not sent or null, the rule keeps its existing value
    If missing_series_evals_to_resolve > 0: updates to that value
    If missing_series_evals_to_resolve = 0: resets to default (nil).
    AlertRule.MissingSeriesEvalsToResolve can't be 0, so I used it to reset

In the Provisioning API, the value is just set if present and > 0. Otherwise it's reset:

PUT to /api/v1/provisioning/alert-rules/{UID}:

    If missing_series_evals_to_resolve is nil, it's reset to the default value
    If missing_series_evals_to_resolve > 0, it's updated

pkg/services/ngalert/api/validation/api_ruler_validation.go

@@ -13,6 +13,7 @@ import (
 	ngmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
 	"github.com/grafana/grafana/pkg/services/ngalert/store"
 	"github.com/grafana/grafana/pkg/setting"
+	"github.com/grafana/grafana/pkg/util"
 	prommodels "github.com/prometheus/common/model"
 )
 
@@ -65,14 +66,15 @@ func ValidateRuleNode(
 	queries := AlertQueriesFromApiAlertQueries(ruleNode.GrafanaManagedAlert.Data)
 
 	newAlertRule := ngmodels.AlertRule{
-		OrgID:           orgId,
-		Title:           ruleNode.GrafanaManagedAlert.Title,
-		Condition:       ruleNode.GrafanaManagedAlert.Condition,
-		Data:            queries,
-		UID:             ruleNode.GrafanaManagedAlert.UID,
-		IntervalSeconds: intervalSeconds,
-		NamespaceUID:    namespaceUID,
-		RuleGroup:       groupName,
+		OrgID:                       orgId,
+		Title:                       ruleNode.GrafanaManagedAlert.Title,
+		Condition:                   ruleNode.GrafanaManagedAlert.Condition,
+		Data:                        queries,
+		UID:                         ruleNode.GrafanaManagedAlert.UID,
+		IntervalSeconds:             intervalSeconds,
+		NamespaceUID:                namespaceUID,
+		RuleGroup:                   groupName,
+		MissingSeriesEvalsToResolve: ruleNode.GrafanaManagedAlert.MissingSeriesEvalsToResolve,
 	}
 
 	if isRecordingRule {
@@ -152,6 +154,11 @@ func validateAlertingRuleFields(in *apimodels.PostableExtendedRuleNode, newRule
 		}
 	}
 
+	newRule.MissingSeriesEvalsToResolve, err = validateMissingSeriesEvalsToResolve(in)
+	if err != nil {
+		return ngmodels.AlertRule{}, err
+	}
+
 	newRule.For, err = validateForInterval(in)
 	if err != nil {
 		return ngmodels.AlertRule{}, err
@@ -293,6 +300,29 @@ func validateKeepFiringForInterval(ruleNode *apimodels.PostableExtendedRuleNode)
 	return duration, nil
 }
 
+// validateMissingSeriesEvalsToResolve validates MissingSeriesEvalsToResolve and converts it to *int.
+// If the ruleNode.GrafanaManagedAlert.MissingSeriesEvalsToResolve is:
+//   - == 0, returns nil (reset to default)
+//   - == nil && UID == "", returns nil (new rule)
+//   - == nil && UID != "", returns -1 (existing rule)
+func validateMissingSeriesEvalsToResolve(ruleNode *apimodels.PostableExtendedRuleNode) (*int, error) {
+	if ruleNode.GrafanaManagedAlert.MissingSeriesEvalsToResolve == nil {
+		if ruleNode.GrafanaManagedAlert.UID != "" {
+			return util.Pointer(-1), nil // will be patched later with the real value of the current version of the rule
+		}
+		return nil, nil // if it's a new rule, use nil as the default
+	}
+
+	v := ruleNode.GrafanaManagedAlert.MissingSeriesEvalsToResolve
+	if *v == 0 {
+		return nil, nil // allow to reset the value to default when 0 is sent
+	} else if *v < 0 {
+		return nil, fmt.Errorf("field `missing_series_evals_to_resolve` cannot be negative [%v]. 0 or any positive number are allowed", *v)
+	}
+
+	return v, nil
+}
+
 // ValidateRuleGroup validates API model (definitions.PostableRuleGroupConfig) and converts it to a collection of models.AlertRule.
 // Returns a slice that contains all rules described by API model or error if either group specification or an alert definition is not valid.
 // It also returns a map containing current existing alerts that don't contain the is_paused field in the body of the call.