fix: clone QueryOptions before modifying LastStatement field

conn.go

@@ -639,9 +639,10 @@ func (c *conn) runDMLBatch(ctx context.Context) (SpannerResult, error) {
 
 	statements := c.batch.statements
 	options := c.batch.options
-	options.QueryOptions.LastStatement = true
+	localOptions := *options
+	localOptions.QueryOptions.LastStatement = true
 	c.batch = nil
-	return c.execBatchDML(ctx, statements, options)
+	return c.execBatchDML(ctx, statements, &localOptions)
 }
 
 func (c *conn) abortBatch() (driver.Result, error) {
@@ -1785,13 +1786,14 @@ func (c *conn) executeAutoPartitionedQuery(ctx context.Context, cancel context.C
 
 func queryInNewRWTransaction(ctx context.Context, c *spanner.Client, statement spanner.Statement, statementInfo *parser.StatementInfo, options *ExecOptions) (rowIterator, *spanner.CommitResponse, error) {
 	var result *wrappedRowIterator
-	options.QueryOptions.LastStatement = true
+	queryOptions := options.QueryOptions
+	queryOptions.LastStatement = true
 	fn := func(ctx context.Context, tx *spanner.ReadWriteTransaction) error {
 		if result != nil {
 			// in case of a retry
 			result.Stop()
 		}
-		it := tx.QueryWithOptions(ctx, statement, options.QueryOptions)
+		it := tx.QueryWithOptions(ctx, statement, queryOptions)
 		row, err := it.Next()
 		if err == iterator.Done {
 			result = &wrappedRowIterator{
@@ -1825,10 +1827,11 @@ var errInvalidDmlForExecContext = spanner.ToSpannerError(status.Error(codes.Fail
 
 func execInNewRWTransaction(ctx context.Context, c *spanner.Client, statement spanner.Statement, statementInfo *parser.StatementInfo, options *ExecOptions) (*result, *spanner.CommitResponse, error) {
 	var res *result
-	options.QueryOptions.LastStatement = true
+	queryOptions := options.QueryOptions
+	queryOptions.LastStatement = true
 	fn := func(ctx context.Context, tx *spanner.ReadWriteTransaction) error {
 		var err error
-		res, err = execTransactionalDML(ctx, tx, statement, statementInfo, options.QueryOptions)
+		res, err = execTransactionalDML(ctx, tx, statement, statementInfo, queryOptions)
 		if err != nil {
 			return err
 		}

stmt_with_mockserver_test.go

@@ -943,3 +943,83 @@ func executeParamTest(t *testing.T, test paramTest, server *testutil.MockedSpann
 		}
 	}
 }
+
+func TestPrepareStmtGORMSharedOptionsBug(t *testing.T) {
+	t.Parallel()
+
+	db, server, teardown := setupTestDBConnection(t)
+	defer teardown()
+	ctx := context.Background()
+
+	// Mock the update query.
+	query := "update test set value = ? where id = ?"
+	if err := server.TestSpanner.PutStatementResult(
+		"update test set value = @p1 where id = @p2",
+		&testutil.StatementResult{
+			Type:        testutil.StatementResultUpdateCount,
+			UpdateCount: 1,
+		},
+	); err != nil {
+		t.Fatal(err)
+	}
+
+	// 1. Prepare statement.
+	stmt, err := db.PrepareContext(ctx, query)
+	if err != nil {
+		t.Fatalf("failed to prepare query: %v", err)
+	}
+	defer stmt.Close()
+
+	// 2. Execute statement outside transaction (auto-commit).
+	_, err = stmt.ExecContext(ctx, "val1", int64(1))
+	if err != nil {
+		t.Fatalf("failed auto-commit execution: %v", err)
+	}
+
+	// 3. Start explicit transaction.
+	tx, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		t.Fatalf("failed to begin transaction: %v", err)
+	}
+
+	// 4. Execute the cached statement inside transaction using tx.Stmt().
+	txStmt := tx.Stmt(stmt)
+	_, err = txStmt.ExecContext(ctx, "val2", int64(1))
+	if err != nil {
+		_ = tx.Rollback()
+		t.Fatalf("failed in-transaction statement execution: %v", err)
+	}
+
+	// 5. Execute another statement in the same transaction.
+	_, err = tx.ExecContext(ctx, "update test set value = ? where id = ?", "val3", int64(2))
+	if err != nil {
+		_ = tx.Rollback()
+		t.Fatalf("failed second in-transaction execution: %v", err)
+	}
+
+	// 6. Commit transaction.
+	if err := tx.Commit(); err != nil {
+		t.Fatalf("failed to commit: %v", err)
+	}
+
+	// 7. Verify mock server requests.
+	requests := server.TestSpanner.DrainRequestsFromServer()
+	executeRequests := testutil.RequestsOfType(requests, reflect.TypeOf(&spannerpb.ExecuteSqlRequest{}))
+	if g, w := len(executeRequests), 3; g != w {
+		t.Fatalf("number of execute requests mismatch\n Got: %v\nWant: %v", g, w)
+	}
+
+	req1 := executeRequests[0].(*spannerpb.ExecuteSqlRequest) // auto-commit outside transaction
+	req2 := executeRequests[1].(*spannerpb.ExecuteSqlRequest) // first DML in transaction (prepared statement)
+	req3 := executeRequests[2].(*spannerpb.ExecuteSqlRequest) // second DML in transaction
+
+	if !req1.LastStatement {
+		t.Error("Expected LastStatement=true for auto-commit execution, got false")
+	}
+	if req2.LastStatement {
+		t.Error("Expected LastStatement=false for first in-transaction statement, got true")
+	}
+	if req3.LastStatement {
+		t.Error("Expected LastStatement=false for second in-transaction statement, got true")
+	}
+}