Enable Session.ExecuteBatchCAS() to return underlying scan errors

The patch enables Session.ExecuteBatchCAS() to return an error which may happen
during rows scanning.

Patch by Bohdan Siryk; reviewed by <> for CASSGO-47

Author: worryg0d

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Retry policy now takes into account query idempotency (CASSGO-27)
 - Don't return error to caller with RetryType Ignore (CASSGO-28)
+- Enable Session.ExecuteBatchCAS() to return underlying scan errors (CASSGO-47)
 
 ## [1.7.0] - 2024-09-23
 

cassandra_test.go

@@ -503,6 +503,18 @@ func TestCAS(t *testing.T) {
 			t.Fatal("scan:", err)
 		}
 	}
+
+	notAppliedBatch := session.Batch(LoggedBatch)
+	notAppliedBatch.Query("INSERT INTO cas_table (title, revid, last_modified) VALUES (?, ?, ?) IF NOT EXISTS", title, revid, modified)
+	// This record is already inserted into the table so C* should return [applied] = false and previous record state,
+	// but we didn't provide any destination variables to handle result, so it should return an error
+	if applied, _, err := session.ExecuteBatchCAS(successBatch); err == nil {
+		t.Fatal("should fail because of lacking of destination variables")
+	} else if applied {
+		t.Fatalf("insert should have not been applied")
+	} else if !strings.Contains(err.Error(), "gocql: not enough columns to scan into") {
+		t.Fatalf("should have failed because of invalid destination variables, but failed because: %v", err)
+	}
 }
 
 func TestDurationType(t *testing.T) {

session.go

@@ -769,7 +769,7 @@ func (s *Session) ExecuteBatch(batch *Batch) error {
 // ExecuteBatchCAS executes a batch operation and returns true if successful and
 // an iterator (to scan additional rows if more than one conditional statement)
 // was sent.
-// Further scans on the interator must also remember to include
+// Further scans on the iterator must also remember to include
 // the applied boolean as the first argument to *Iter.Scan
 func (s *Session) ExecuteBatchCAS(batch *Batch, dest ...interface{}) (applied bool, iter *Iter, err error) {
 	iter = s.executeBatch(batch)
@@ -785,7 +785,7 @@ func (s *Session) ExecuteBatchCAS(batch *Batch, dest ...interface{}) (applied bo
 		iter.Scan(&applied)
 	}
 
-	return applied, iter, nil
+	return applied, iter, iter.err
 }
 
 // MapExecuteBatchCAS executes a batch operation much like ExecuteBatchCAS,