Workaround empty REGEXP pattern support for MySQL 5.x

src/Persistence/Sql/Mysql/Query.php

@@ -61,7 +61,7 @@ protected function _renderConditionRegexpOperator(bool $negated, string $sqlLeft
 
         return $sqlLeft . ($negated ? ' not' : '') . ' regexp ' . (
             $isMysql5x
-                ? $sqlRight
+                ? 'concat(' . $this->escapeStringLiteral('@?') . ', ' . $sqlRight . ')' // https://dbfiddle.uk/diAepf8V
                 : 'concat(' . $this->escapeStringLiteral('(?s)') . ', ' . $sqlRight . ')'
         );
     }

tests/ConditionSqlTest.php

@@ -833,15 +833,6 @@ public function testRegexpCondition(string $type, bool $isBinary): void
     #[DataProvider('provideNullLikeRegexpConditionCases')]
     public function testNullLikeRegexpCondition(string $operator, ?bool $expectedResult, ?string $value, ?string $pattern, bool $negated): void
     {
-        if ($this->getDatabasePlatform() instanceof MySQLPlatform
-            && !MysqlConnection::isServerMariaDb($this->getConnection())
-            && MysqlConnection::getServerMinorVersion($this->getConnection()) < 600
-            && $operator === 'regexp' && $pattern === ''
-        ) {
-            // https://dbfiddle.uk/diAepf8V
-            self::markTestIncomplete('MySQL 5.x does not support REGEXP with empty pattern');
-        }
-
         if ($this->getDatabasePlatform() instanceof SQLServerPlatform && $operator === 'regexp') {
             // https://devblogs.microsoft.com/azure-sql/introducing-regular-expression-regex-support-in-azure-sql-db/
             self::markTestIncomplete('MSSQL has no REGEXP support yet');

tests/Persistence/Sql/QueryTest.php

@@ -878,11 +878,15 @@ public function testWhereSpecialValues(): void
                     EOF,
             (new SqliteQuery('[where]'))->where($this->e('sum({})', ['a']), 'like', $this->e('sum({})', ['b']))->render()[0]
         );
-        foreach (['8.0.0', 'MariaDB-11.0.0'] as $serverVersion) {
+        foreach (['5.7.0', '8.0.0', 'MariaDB-11.0.0'] as $serverVersion) {
             self::assertSame(
-                <<<'EOF'
-                    where `name` like regexp_replace(:a, '\\\\\\\\|\\\\(?![_%])', '\\\\\\\\') escape '\\'
-                    EOF,
+                $serverVersion === '5.7.0'
+                    ? <<<'EOF'
+                        where `name` like replace(replace(replace(replace(replace(replace(replace(replace(:a, '\\\\', '\\\\*'), '\\_', '\\_*'), '\\%', '\\%*'), '\\', '\\\\'), '\\\\_*', '\\_'), '\\\\%*', '\\%'), '\\\\\\\\*', '\\\\'), '%\\', '%\\\\') escape '\\'
+                        EOF
+                    : <<<'EOF'
+                        where `name` like regexp_replace(:a, '\\\\\\\\|\\\\(?![_%])', '\\\\\\\\') escape '\\'
+                        EOF,
                 $this->createMysqlQuery($serverVersion, '[where]')->where('name', 'like', 'foo')->render()[0]
             );
         }
@@ -942,9 +946,11 @@ public function testWhereSpecialValues(): void
                     EOF,
             (new SqliteQuery('[where]'))->where($this->e('sum({})', ['a']), 'regexp', $this->e('sum({})', ['b']))->render()[0]
         );
-        foreach (['8.0.0', 'MariaDB-11.0.0'] as $serverVersion) {
+        foreach (['5.7.0', '8.0.0', 'MariaDB-11.0.0'] as $serverVersion) {
             self::assertSame(
-                'where `name` regexp concat(\'(?s)\', :a)',
+                $serverVersion === '5.7.0'
+                    ? 'where `name` regexp concat(\'@?\', :a)'
+                    : 'where `name` regexp concat(\'(?s)\', :a)',
                 $this->createMysqlQuery($serverVersion, '[where]')->where('name', 'regexp', 'foo')->render()[0]
             );
         }
@@ -1646,7 +1652,7 @@ public function testWith(): void
         self::assertSame('with recursive "q11" ("foo", "qwe""ry") as (select "salary" from "salaries"),' . "\n"
             . '"q12" ("bar", "baz") as (select "salary" from "salaries")' . "\n" . 'select * from "q11", "q12"', $q2->render()[0]);
 
-        // now test some more useful reql life query
+        // now test some more useful real life query
         $quotes = $this->q()
             ->table('quotes')
             ->field('emp_id')