refactor[discovery, tsdb]: simplify error handling and remove redundant checks (prometheus#16328)

* refactor: simplify error handling and remove redundant checks

Signed-off-by: Ryan Wu <rongjun0821@gmail.com>

* Add the comment for return of reloading blocks failure

Co-authored-by: Ayoub Mrini <ayoubmrini424@gmail.com>
Signed-off-by: Ryan Wu <rongjun0821@gmail.com>

* Add the comment for return of reloading blocks failure

Signed-off-by: Ryan Wu <rongjun0821@gmail.com>

---------

Signed-off-by: Ryan Wu <rongjun0821@gmail.com>
Co-authored-by: Ayoub Mrini <ayoubmrini424@gmail.com>

Author: ryanwuer

discovery/openstack/loadbalancer.go

@@ -189,9 +189,5 @@ func (i *LoadBalancerDiscovery) refresh(ctx context.Context) ([]*targetgroup.Gro
 		tg.Targets = append(tg.Targets, labels)
 	}
 
-	if err != nil {
-		return nil, err
-	}
-
 	return []*targetgroup.Group{tg}, nil
 }

discovery/vultr/vultr.go

@@ -16,7 +16,6 @@ package vultr
 import (
 	"context"
 	"errors"
-	"fmt"
 	"log/slog"
 	"net"
 	"net/http"
@@ -137,10 +136,6 @@ func NewDiscovery(conf *SDConfig, logger *slog.Logger, metrics discovery.Discove
 
 	d.client.SetUserAgent(version.PrometheusUserAgent())
 
-	if err != nil {
-		return nil, fmt.Errorf("error setting up vultr agent: %w", err)
-	}
-
 	d.Discovery = refresh.NewDiscovery(
 		refresh.Options{
 			Logger:              logger,

tsdb/db.go

@@ -2280,10 +2280,9 @@ func (db *DB) CleanTombstones() (err error) {
 					db.logger.Error("failed to delete block after failed `CleanTombstones`", "dir", dir, "err", err)
 				}
 			}
-			if err != nil {
-				return fmt.Errorf("reload blocks: %w", err)
-			}
-			return nil
+
+			// This should only be reached if an error occurred.
+			return fmt.Errorf("reload blocks: %w", err)
 		}
 	}
 	return nil

tsdb/db_test.go

@@ -9104,7 +9104,7 @@ func compareSeries(t require.TestingT, expected, actual map[string][]chunks.Samp
 				require.Equal(t, eS.F(), aS.F(), "sample %d in series %q differs", i, key)
 			case chunkenc.ValHistogram:
 				eH, aH := eS.H(), aS.H()
-				if aH.CounterResetHint == histogram.UnknownCounterReset && aH.CounterResetHint != histogram.GaugeType {
+				if aH.CounterResetHint == histogram.UnknownCounterReset {
 					eH = eH.Copy()
 					// It is always safe to set the counter reset hint to UnknownCounterReset
 					eH.CounterResetHint = histogram.UnknownCounterReset
@@ -9114,7 +9114,7 @@ func compareSeries(t require.TestingT, expected, actual map[string][]chunks.Samp
 
 			case chunkenc.ValFloatHistogram:
 				eFH, aFH := eS.FH(), aS.FH()
-				if aFH.CounterResetHint == histogram.UnknownCounterReset && aFH.CounterResetHint != histogram.GaugeType {
+				if aFH.CounterResetHint == histogram.UnknownCounterReset {
 					eFH = eFH.Copy()
 					// It is always safe to set the counter reset hint to UnknownCounterReset
 					eFH.CounterResetHint = histogram.UnknownCounterReset