Preserve bulk additions through the conflict column view

Author: minleejae

src/main/java/net/sf/jsqlparser/statement/insert/InsertConflictTarget.java

@@ -103,6 +103,21 @@ public void add(int index, String name) {
                         new Index.ColumnParams(name));
             }
 
+            @Override
+            public boolean addAll(Collection<? extends String> names) {
+                return addAll(size(), names);
+            }
+
+            @Override
+            public boolean addAll(int index, Collection<? extends String> names) {
+                int insertionIndex = index == size() ? indexElements.size() : elementIndex(index);
+                List<Index.ColumnParams> additions = new ArrayList<>();
+                for (String name : names) {
+                    additions.add(new Index.ColumnParams(name));
+                }
+                return indexElements.addAll(insertionIndex, additions);
+            }
+
             @Override
             public String remove(int index) {
                 return indexElements.remove(elementIndex(index)).getColumnName();

src/test/java/net/sf/jsqlparser/statement/insert/PostgreSQLConflictTargetTest.java

@@ -110,6 +110,19 @@ void retainsMutableLegacyColumnViewAndReplacementMethods() throws Exception {
         assertTrue(target.getIndexElements().isEmpty());
     }
 
+    @Test
+    void bulkColumnAdditionsSnapshotTheMutableView() {
+        InsertConflictTarget target = new InsertConflictTarget("id", null, null, null);
+        List<String> names = target.getIndexColumnNames();
+        assertTrue(target.addAllIndexColumnNames(names));
+        assertEquals(List.of("id", "id"), names);
+        assertTrue(names.addAll(names));
+        assertEquals(4, names.size());
+        assertTrue(names.addAll(1, names.subList(0, 2)));
+        assertEquals(6, names.size());
+        assertFalse(names.addAll(List.of()));
+    }
+
     @Test
     void statementVisitorTraversesTargetExpressions() throws Exception {
         Insert insert = (Insert) CCJSqlParserUtil.parse("INSERT INTO users VALUES (1) "