Ruler: Move inner eval function (#15688)

Refactoring in prevision of https://github.com/prometheus/prometheus/pull/15681

By moving the `eval` function outside of the for loop, we can modify the rule execution order more easily (without huge git changes)

Signed-off-by: Julien Duchesne <julien.duchesne@grafana.com>

rules/group.go

@@ -23,6 +23,9 @@ import (
 	"sync"
 	"time"
 
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
 	"go.uber.org/atomic"
 
 	"github.com/prometheus/prometheus/promql/parser"
@@ -30,9 +33,6 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/common/promslog"
-	"go.opentelemetry.io/otel"
-	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/codes"
 
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/model/timestamp"
@@ -512,18 +512,8 @@ func (g *Group) CopyState(from *Group) {
 func (g *Group) Eval(ctx context.Context, ts time.Time) {
 	var (
 		samplesTotal    atomic.Float64
-		wg           sync.WaitGroup
+		ruleQueryOffset = g.QueryOffset()
 	)
-
-	ruleQueryOffset := g.QueryOffset()
-
-	for i, rule := range g.rules {
-		select {
-		case <-g.done:
-			return
-		default:
-		}
-
 	eval := func(i int, rule Rule, cleanup func()) {
 		if cleanup != nil {
 			defer cleanup()
@@ -656,6 +646,14 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 		}
 	}
 
+	var wg sync.WaitGroup
+	for i, rule := range g.rules {
+		select {
+		case <-g.done:
+			return
+		default:
+		}
+
 		if ctrl := g.concurrencyController; ctrl.Allow(ctx, g, rule) {
 			wg.Add(1)
 
@@ -667,7 +665,6 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 			eval(i, rule, nil)
 		}
 	}
-
 	wg.Wait()
 
 	g.metrics.GroupSamples.WithLabelValues(GroupKey(g.File(), g.Name())).Set(samplesTotal.Load())