fix: end block comments at the first */ for dialects that do not nest

consumeBlockCommentBody honoured nested block comments under every
dialect, so a /* inside a comment opened another level and the comment
ran on to a later */. MySQL, MariaDB, SQLite, Oracle, BigQuery and
Spanner end a block comment at the first */ and run what follows it,
so with Dialect.MYSQL the parser returned SELECT 1 for
SELECT 1 /* a /* b */ + 2 -- */, which the server evaluates as
SELECT 1 + 2.

Dialect gains isNestedBlockComments(), false for those six dialects,
and the token manager nests only when the configured dialect does.
Without a dialect, and for PostgreSQL, SQL Server, H2 and the other
dialects, nesting is unchanged.

Author: tanjiroK-coder

src/main/java/net/sf/jsqlparser/parser/AbstractJSqlParser.java

@@ -51,6 +51,11 @@ public enum Dialect {
                                                         Feature.allowBackslashEscapeCharacter), SNOWFLAKE(
                                                                 Feature.allowBackslashEscapeCharacter), INFORMIX, SPANNER, DORIS, COCKROACHDB, TERADATA, SQLITE;
 
+        // MySQL, MariaDB, SQLite, Oracle, BigQuery and Spanner document that block comments do
+        // not nest: the first closing delimiter ends the comment.
+        private static final Set<Dialect> FLAT_BLOCK_COMMENT_DIALECTS =
+                EnumSet.of(MYSQL, MARIADB, ORACLE, SQLITE, BIGQUERY, SPANNER);
+
         private final Set<Feature> lexerFeatures;
         private final AdjacentStringLiterals adjacentStringLiterals;
 
@@ -72,6 +77,15 @@ public Set<Feature> getLexerFeatures() {
         public AdjacentStringLiterals getAdjacentStringLiterals() {
             return adjacentStringLiterals;
         }
+
+        /**
+         * Whether a {@code /*} inside a block comment opens a nested comment that needs its own
+         * closing {@code *}{@code /}, as in the SQL standard, PostgreSQL, SQL Server or H2. The
+         * other dialects end the comment at the first closing delimiter.
+         */
+        public boolean isNestedBlockComments() {
+            return !FLAT_BLOCK_COMMENT_DIALECTS.contains(this);
+        }
     }
 
     public P withSquareBracketQuotation() {

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -3918,17 +3918,18 @@ TOKEN_MGR_DECLS : {
 
     /**
      * Consumes the body of a block comment after the opening delimiter has been matched,
-     * honouring nesting, up to and including the outermost closing delimiter. Then backs
-     * up 2 characters so the MULTI_LINE_COMMENT rule matches the closing delimiter and
-     * terminates the MORE chain.
+     * honouring nesting where the dialect nests, up to and including the outermost closing
+     * delimiter. Then backs up 2 characters so the MULTI_LINE_COMMENT rule matches the
+     * closing delimiter and terminates the MORE chain.
      */
     void consumeBlockCommentBody() {
+        boolean nested = isNestedBlockCommentDialect();
         int nesting = 1;
         char prev = 0;
         try {
             while (nesting > 0) {
                 char c = input_stream.readChar();
-                if (prev == '/' && c == '*') {
+                if (nested && prev == '/' && c == '*') {
                     nesting++;
                     prev = 0;
                 } else if (prev == '*' && c == '/') {
@@ -3944,6 +3945,18 @@ TOKEN_MGR_DECLS : {
             // manager raise the lexical error from IN_BLOCK_COMMENT.
         }
     }
+
+    // Without a dialect block comments nest as in the SQL standard. A dialect whose server ends
+    // the comment at the first closing delimiter must not hide the SQL that follows it.
+    private boolean isNestedBlockCommentDialect() {
+        Object dialect = configuration.getValue(Feature.dialect);
+        for (AbstractJSqlParser.Dialect candidate : AbstractJSqlParser.Dialect.values()) {
+            if (candidate.name().equals(dialect)) {
+                return candidate.isNestedBlockComments();
+            }
+        }
+        return true;
+    }
 }
 
 SKIP:

src/test/java/net/sf/jsqlparser/statement/select/NestedCommentTest.java

@@ -9,9 +9,13 @@
  */
 package net.sf.jsqlparser.statement.select;
 
+import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.parser.AbstractJSqlParser.Dialect;
 import net.sf.jsqlparser.parser.CCJSqlParserUtil;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
 
 import static org.junit.jupiter.api.Assertions.*;
 
@@ -102,4 +106,36 @@ void testMultilineNestedComment() {
     void testOracleHintPreserved() {
         assertParses("SELECT /*+ FULL(t) */ * FROM t");
     }
+
+    private static String parse(String sql, Dialect dialect) throws JSQLParserException {
+        return CCJSqlParserUtil.parse(sql, p -> p.withDialect(dialect)).toString();
+    }
+
+    @ParameterizedTest
+    @EnumSource(value = Dialect.class,
+            names = {"MYSQL", "MARIADB", "ORACLE", "SQLITE", "BIGQUERY", "SPANNER"})
+    void testBlockCommentEndsAtFirstDelimiterWhereTheServerDoes(Dialect dialect)
+            throws JSQLParserException {
+        assertFalse(dialect.isNestedBlockComments());
+        assertEquals("SELECT 1 + 2", parse("SELECT 1 /* a /* b */ + 2 -- */", dialect));
+        assertEquals("SELECT 1 + 2", parse("SELECT 1 /* a /* b */ + 2", dialect));
+        assertEquals("SELECT 1", parse("SELECT 1 /* a /* b */ /* c */", dialect));
+        assertThrows(JSQLParserException.class, () -> parse("SELECT 1 /* a /* b */ */", dialect));
+        assertThrows(JSQLParserException.class, () -> parse("SELECT 1 /* a /* b", dialect));
+    }
+
+    @ParameterizedTest
+    @EnumSource(value = Dialect.class, names = {"ANSI_SQL", "POSTGRESQL", "SQLSERVER", "H2"})
+    void testBlockCommentNestsWhereTheServerDoes(Dialect dialect) throws JSQLParserException {
+        assertTrue(dialect.isNestedBlockComments());
+        assertEquals("SELECT 1", parse("SELECT 1 /* a /* b */ + 2 -- */", dialect));
+        assertEquals("SELECT 1 + 2", parse("SELECT 1 /* a /* b */ c */ + 2", dialect));
+        assertThrows(JSQLParserException.class, () -> parse("SELECT 1 /* a /* b */", dialect));
+    }
+
+    @Test
+    void testBlockCommentNestsWithoutDialect() throws JSQLParserException {
+        assertEquals("SELECT 1",
+                CCJSqlParserUtil.parse("SELECT 1 /* a /* b */ + 2 -- */").toString());
+    }
 }