avoid quadratic string concatenation in FullTextSearch.toString (#2859)

Author: tanjiroK-coder

src/main/java/net/sf/jsqlparser/expression/operators/relational/FullTextSearch.java

@@ -75,13 +75,13 @@ public <T, S> T accept(ExpressionVisitor<T> expressionVisitor, S context) {
     @Override
     public String toString() {
         // Build a list of matched columns
-        String columnsListCommaSeperated = "";
+        StringBuilder columnsListCommaSeperated = new StringBuilder();
         Iterator<Column> iterator = this._matchColumns.iterator();
         while (iterator.hasNext()) {
             Column col = iterator.next();
-            columnsListCommaSeperated += col.getFullyQualifiedName();
+            columnsListCommaSeperated.append(col.getFullyQualifiedName());
             if (iterator.hasNext()) {
-                columnsListCommaSeperated += ",";
+                columnsListCommaSeperated.append(",");
             }
         }
 

src/test/java/net/sf/jsqlparser/expression/operators/relational/FullTextSearchExpressionTest.java

@@ -9,7 +9,15 @@
  */
 package net.sf.jsqlparser.expression.operators.relational;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;
+
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.List;
 import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.expression.StringValue;
+import net.sf.jsqlparser.schema.Column;
 import net.sf.jsqlparser.test.TestUtils;
 import org.junit.jupiter.api.Test;
 
@@ -35,4 +43,18 @@ public void testIssue1223() throws JSQLParserException {
                 + "full_text desc",
                 true);
     }
+
+    @Test
+    public void testToStringIsLinearInMatchColumns() {
+        List<Column> columns = new ArrayList<>();
+        for (int i = 0; i < 200_000; i++) {
+            columns.add(new Column("c" + i));
+        }
+        FullTextSearch fullTextSearch = new FullTextSearch()
+                .withMatchColumns(new ExpressionList<>(columns))
+                .withAgainstValue(new StringValue("x"));
+
+        String sql = assertTimeoutPreemptively(Duration.ofSeconds(2), fullTextSearch::toString);
+        assertThat(sql).startsWith("MATCH (c0,c1,").endsWith(",c199999) AGAINST ('x')");
+    }
 }