Fix jdbc-v2: nest /* */ block comments in the ANTLR4 lexer

CHANGELOG.md

@@ -96,6 +96,13 @@
 
 ### Bug Fixes 
 
+- **[jdbc-v2]** Fixed the ANTLR4 lexer not nesting `/* */` block comments. ClickHouse (and the JavaCC parser backend)
+  raise the nesting level on an inner `/*` and close the comment only at the matching `*/`, while the ANTLR4 lexer ended
+  the comment at the first `*/` and lexed the rest of it as SQL. With the `ANTLR4` / `ANTLR4_PARAMS_PARSER` backends this
+  made statements the server accepts (e.g. `SELECT 1 /* ) /* ) */ ) */, 2`) report syntax errors, and made
+  `ANTLR4_PARAMS_PARSER` count a `?` inside the nested part of a comment as a bind parameter. Comments that do not nest
+  are unaffected; an unterminated block comment is now skipped to the end of the statement instead of being lexed as
+  stray tokens. (https://github.com/ClickHouse/clickhouse-java/issues/3021)
 - **[client-v2]** Fixed reading a `SimpleAggregateFunction(func, T)` value held in a `Dynamic` column. The binary type
   encoding of such a value (`0x2E <function_name> <parameters> <arguments> <argument_type_encodings>`) was not consumed
   at all, so the read failed with `IndexOutOfBoundsException`, and the unconsumed encoding bytes would otherwise have

jdbc-v2/src/main/antlr4/com/clickhouse/jdbc/internal/parser/antlr4/ClickHouseLexer.g4

@@ -507,6 +507,14 @@ UNDERSCORE   : '_';
 
 // Comments and whitespace
 
-MULTI_LINE_COMMENT  : '/*' .*? '*/'                            -> skip;
+MULTI_LINE_COMMENT  : '/*'                                     -> skip, pushMode(IN_MULTI_LINE_COMMENT);
 SINGLE_LINE_COMMENT : ('--' | '//' | '#!' | '#') ~('\n' | '\r')* ('\n' | '\r' | EOF) -> skip;
-WHITESPACE          : [ \u000B\u000C\t\r\n]                    -> skip; // '\n' can be part of multiline single query
+WHITESPACE          : [ \u000B\u000C\t\r\n]                    -> skip; // '\n' can be part of multiline single query
+
+// Block comments nest, as they do on the server: the mode stack holds the nesting level, so only the
+// closer matching the outermost '/*' ends the comment.
+mode IN_MULTI_LINE_COMMENT;
+
+NESTED_MULTI_LINE_COMMENT : '/*' -> skip, pushMode(IN_MULTI_LINE_COMMENT);
+MULTI_LINE_COMMENT_END    : '*/' -> skip, popMode;
+MULTI_LINE_COMMENT_BODY   : .    -> skip;

jdbc-v2/src/test/java/com/clickhouse/jdbc/internal/BaseSqlParserFacadeTest.java

@@ -12,6 +12,7 @@
 import java.io.InputStreamReader;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Properties;
 import java.util.stream.Collectors;
@@ -1029,6 +1030,52 @@ public static Object[][] testStatementWithoutResultSetDP() {
         };
     }
 
+    @Test(dataProvider = "testBlockCommentNestingDP")
+    public void testBlockCommentNesting(String sql, int[] paramPositions, boolean insert, boolean hasResultSet) {
+        ParsedPreparedStatement stmt = parser.parsePreparedStatement(sql);
+        Assert.assertFalse(stmt.isHasErrors(), "Statement has errors: " + sql);
+        assertEquals(stmt.getArgCount(), paramPositions.length, "Args do not match for: " + sql);
+        assertEquals(Arrays.copyOf(stmt.getParamPositions(), stmt.getArgCount()), paramPositions,
+                "Parameter positions do not match for: " + sql);
+        assertEquals(stmt.isInsert(), insert, "Insert type does not match for: " + sql);
+        assertEquals(stmt.isHasResultSet(), hasResultSet, "Result set expectation does not match for: " + sql);
+    }
+
+    @DataProvider
+    public static Object[][] testBlockCommentNestingDP() {
+        StringBuilder deeplyNested = new StringBuilder("SELECT ");
+        for (int i = 0; i < 64; i++) {
+            deeplyNested.append("/*");
+        }
+        deeplyNested.append(" x ");
+        for (int i = 0; i < 64; i++) {
+            deeplyNested.append("*/");
+        }
+        deeplyNested.append(" ?");
+
+        return new Object[][]{
+                // nested block comments
+                {"SELECT 1 /* ) /* ) */ ) */, ?", new int[]{28}, false, true},
+                {"SELECT /* a /* b */ c */ ?", new int[]{25}, false, true},
+                {"SELECT /* ? /* ? */ ? */ ?", new int[]{25}, false, true},
+                {"SELECT /* a\n/* b\n*/ c\n*/ ?", new int[]{25}, false, true},
+                {"SELECT /* /* /* x */ */ */ ?", new int[]{27}, false, true},
+                {"SELECT 1 /* ; /* ; */ ; */, ?", new int[]{28}, false, true},
+                {"/* a /* ? */ b */ SELECT ? /* c /* ? */ d */", new int[]{25}, false, true},
+                {"SELECT ? FROM t WHERE a = /* x /* ? */ y */ ? AND b = 1", new int[]{7, 44}, false, true},
+                {deeplyNested.toString(), new int[]{deeplyNested.length() - 1}, false, true},
+                {"INSERT INTO t (a, b) VALUES (1 /* ) /* ) */ ) */, ?)", new int[]{50}, true, false},
+                {"INSERT INTO t /* c1 /* c2 */ c3 */ (a) VALUES (?)", new int[]{47}, true, false},
+
+                // not nested - existing behaviour that must stay unchanged
+                {"SELECT /* plain comment ? */ ?", new int[]{29}, false, true},
+                {"SELECT /**/ ?", new int[]{12}, false, true},
+                {"SELECT 1 /*/ 2 */, ?", new int[]{19}, false, true},
+                {"SELECT '/* not a comment */' AS a, ?", new int[]{35}, false, true},
+                {"INSERT INTO t (a, b) VALUES (1 /* plain */, ?)", new int[]{44}, true, false},
+        };
+    }
+
     /**
      * Reads SQL keywords from the resource file.
      * Keywords are listed one per line, comments start with #.