policer: Do not mutate slice under iteration

Nothing wrong with it, besides being difficult to read.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/services/policer/check.go

@@ -110,6 +110,7 @@ func (p *Policer) processRepNodes(ctx context.Context, requirements *placementRe
 
 	// Number of copies that are stored on maintenance nodes.
 	var uncheckedCopies int
+	var candidates []netmap.NodeInfo
 	for i := 0; shortage > 0 && i < len(nodes); i++ {
 		select {
 		case <-ctx.Done():
@@ -125,9 +126,9 @@ func (p *Policer) processRepNodes(ctx context.Context, requirements *placementRe
 			checkedNodes.set(nodes[i], st)
 			if st == nodeDoesNotHoldObject {
 				// 1. The node does not hold object (`st == nodeDoesNotHoldObject`).
-				// 2. This is the first time the node is encountered (`!cached``).
-				// So we leave the node in the list and skip its removal
-				// at the end of the loop body.
+				// 2. This is the first time the node is encountered (`!cached`).
+				// So we need to try to put an object to it.
+				candidates = append(candidates, nodes[i])
 				continue
 			}
 		}
@@ -153,12 +154,9 @@ func (p *Policer) processRepNodes(ctx context.Context, requirements *placementRe
 		default:
 			panic("unreachable")
 		}
-
-		nodes = append(nodes[:i], nodes[i+1:]...)
-		i--
 	}
 
-	p.handleProcessNodesResult(ctx, addr, requirements, nodes, checkedNodes, shortage, uncheckedCopies)
+	p.handleProcessNodesResult(ctx, addr, requirements, candidates, checkedNodes, shortage, uncheckedCopies)
 }
 
 func (p *Policer) checkStatus(ctx context.Context, addr oid.Address, node netmap.NodeInfo) (nodeProcessStatus, error) {