Support for nested multiline comments

src/Parsers/Lexer.cpp

@@ -253,15 +253,27 @@ Token Lexer::nextTokenImpl()
                 else
                 {
                     ++pos;
+
+                    /// Nested multiline comments are supported according to the SQL standard.
+                    size_t nesting_level = 1;
+
                     while (pos + 2 <= end)
                     {
-                        /// This means that nested multiline comments are not supported.
-                        if (pos[0] == '*' && pos[1] == '/')
+                        if (pos[0] == '/' && pos[1] == '*')
                         {
                             pos += 2;
-                            return Token(TokenType::Comment, token_begin, pos);
+                            ++nesting_level;
                         }
-                        ++pos;
+                        else if (pos[0] == '*' && pos[1] == '/')
+                        {
+                            pos += 2;
+                            --nesting_level;
+
+                            if (nesting_level == 0)
+                                return Token(TokenType::Comment, token_begin, pos);
+                        }
+                        else
+                            ++pos;
                     }
                     return Token(TokenType::ErrorMultilineCommentIsNotClosed, token_begin, end);
                 }

tests/queries/0_stateless/01491_nested_multiline_comments.reference

+1
+1
+1

tests/queries/0_stateless/01491_nested_multiline_comments.sql

+SELECT /*/**/*/ 1;
+SELECT /*a/*b*/c*/ 1;
+SELECT /*ab/*cd*/ef*/ 1;