fix(indexer): Ineffective or missing break statements in kv package. …

…(backport cometbft#3557) (cometbft#3564)

Closes cometbft#3544.

### Changes
- Adds missing `for` loop labels in the kv indexer 
- Previously ineffective `break` statements now point to their enclosing
`for` loop labels to exit upon reception on the `ctx.Done()` channel.

---

#### PR checklist

~- [ ] Tests written/updated~
- [x] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
~- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments~
- [x] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec
<hr>This is an automatic backport of pull request cometbft#3557 done by
[Mergify](https://mergify.com).

---------

Co-authored-by: Alessandro <[email protected]>

.changelog/unreleased/bug-fixes/3544-indexer-break-statement.md

@@ -0,0 +1,3 @@
+- `[indexer]` Fixed ineffective select break statements; they now
+  point to their enclosing for loop label to exit
+  ([\#3544](https://github.com/cometbft/cometbft/issues/3544))

state/indexer/block/kv/kv.go

@@ -222,6 +222,8 @@ func (idx *BlockerIndexer) Search(ctx context.Context, q *query.Query) ([]int64,
 	// fetch matching heights
 	results = make([]int64, 0, len(filteredHeights))
 	resultMap := make(map[int64]struct{})
+
+FOR_LOOP:
 	for _, hBz := range filteredHeights {
 		h := int64FromBytes(hBz)
 
@@ -238,7 +240,7 @@ func (idx *BlockerIndexer) Search(ctx context.Context, q *query.Query) ([]int64,
 
 		select {
 		case <-ctx.Done():
-			break
+			break FOR_LOOP
 
 		default:
 		}
@@ -314,8 +316,7 @@ LOOP:
 
 		select {
 		case <-ctx.Done():
-			break
-
+			break LOOP
 		default:
 		}
 	}
@@ -337,6 +338,7 @@ LOOP:
 
 	// Remove/reduce matches in filteredHashes that were not found in this
 	// match (tmpHashes).
+FOR_LOOP:
 	for k, v := range filteredHeights {
 		tmpHeight := tmpHeights[k]
 
@@ -347,8 +349,7 @@ LOOP:
 
 			select {
 			case <-ctx.Done():
-				break
-
+				break FOR_LOOP
 			default:
 			}
 		}
@@ -442,6 +443,7 @@ func (idx *BlockerIndexer) match(
 		}
 		defer it.Close()
 
+	LOOP_EXISTS:
 		for ; it.Valid(); it.Next() {
 			keyHeight, err := parseHeightFromEventKey(it.Key())
 			if err != nil || !checkHeightConditions(heightInfo, keyHeight) {
@@ -451,7 +453,7 @@ func (idx *BlockerIndexer) match(
 
 			select {
 			case <-ctx.Done():
-				break
+				break LOOP_EXISTS
 
 			default:
 			}
@@ -473,6 +475,7 @@ func (idx *BlockerIndexer) match(
 		}
 		defer it.Close()
 
+	LOOP_CONTAINS:
 		for ; it.Valid(); it.Next() {
 			eventValue, err := parseValueFromEventKey(it.Key())
 			if err != nil {
@@ -489,7 +492,7 @@ func (idx *BlockerIndexer) match(
 
 			select {
 			case <-ctx.Done():
-				break
+				break LOOP_CONTAINS
 
 			default:
 			}
@@ -515,14 +518,15 @@ func (idx *BlockerIndexer) match(
 
 	// Remove/reduce matches in filteredHeights that were not found in this
 	// match (tmpHeights).
+FOR_LOOP:
 	for k, v := range filteredHeights {
 		tmpHeight := tmpHeights[k]
 		if tmpHeight == nil || !bytes.Equal(tmpHeight, v) {
 			delete(filteredHeights, k)
 
 			select {
 			case <-ctx.Done():
-				break
+				break FOR_LOOP
 
 			default:
 			}