Improve SQL context loading

- add fallback in case there is no version match
- do not zero one by one, byt by two to match version parts
- better handle corner cases

Fixes phpmyadmin/phpmyadmin#13728

Signed-off-by: Michal Čihař <michal@cihar.com>

Author: nijel

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## [Unreleased]
 
 * Fix parsing of CREATE TABLE with per field COLLATE.
+* Improved Context::loadClosest to better deal with corner cases.
 
 ## [4.2.3] - 2017-10-10
 

src/Context.php

@@ -486,37 +486,31 @@ public static function load($context = '')
      */
     public static function loadClosest($context = '')
     {
-        /**
-         * The number of replaces done by `preg_replace`.
-         * This actually represents whether a new context was generated or not.
-         *
-         * @var int
-         */
-        $count = 0;
-
-        // As long as a new context can be generated, we try to load it.
-        do {
+        $length = strlen($context);
+        for ($i = $length; $i > 0;) {
             try {
-                // Trying to load the new context.
+                /* Trying to load the new context */
                 static::load($context);
+                return $context;
             } catch (LoaderException $e) {
-                // If it didn't work, we are looking for a new one and skipping
-                // over to the next generation that will try the new context.
-                $context = preg_replace(
-                    '/[1-9](0*)$/',
-                    '0$1',
-                    $context,
-                    -1,
-                    $count
-                );
-                continue;
+                /* Replace last two non zero digits by zeroes */
+                do {
+                    $i -= 2;
+                    $part = substr($context, $i, 2);
+                    /* No more numeric parts to strip */
+                    if (! is_numeric($part)) {
+                        break 2;
+                    }
+                } while (intval($part) === 0 && $i > 0);
+                $context = substr($context, 0, $i) . '00' . substr($context, $i + 2);
             }
-
-            // Last generated context was valid (did not throw any exceptions).
-            // So we return it, to let the user know what context was loaded.
-            return $context;
-        } while ($count !== 0);
-
+        }
+        /* Fallback to loading at least matching engine */
+        if (strncmp($context, 'MariaDb', 7) === 0) {
+            return static::loadClosest('MariaDb100300');
+        } elseif (strncmp($context, 'MySql', 5) === 0) {
+            return static::loadClosest('MySql50700');
+        }
         return null;
     }
 

tests/Lexer/ContextTest.php

@@ -14,23 +14,43 @@ public function testLoad()
         $this->assertTrue(isset(Context::$KEYWORDS['STORED']));
         $this->assertFalse(isset(Context::$KEYWORDS['AUTHORS']));
 
-        Context::load('MySql50600');
-        $this->assertEquals('\\PhpMyAdmin\\SqlParser\\Contexts\\ContextMySql50600', Context::$loadedContext);
-        $this->assertFalse(isset(Context::$KEYWORDS['STORED']));
-        $this->assertTrue(isset(Context::$KEYWORDS['AUTHORS']));
-
-        Context::loadClosest('MySql50712');
-        $this->assertEquals('\\PhpMyAdmin\\SqlParser\\Contexts\\ContextMySql50700', Context::$loadedContext);
-
-        $this->assertEquals(null, Context::loadClosest('Sql'));
-
         // Restoring context.
         Context::load('');
         $this->assertEquals('\\PhpMyAdmin\\SqlParser\\Contexts\\ContextMySql50700', Context::$defaultContext);
         $this->assertTrue(isset(Context::$KEYWORDS['STORED']));
         $this->assertFalse(isset(Context::$KEYWORDS['AUTHORS']));
     }
 
+    /**
+     * Test for loading closest SQL context
+     *
+     * @dataProvider contextLoading
+     */
+    public function testLoadClosest($context, $expected)
+    {
+        $this->assertEquals($expected, Context::loadClosest($context));
+        if (! is_null($expected)) {
+            $this->assertEquals('\\PhpMyAdmin\\SqlParser\\Contexts\\Context' . $expected, Context::$loadedContext);
+            $this->assertTrue(class_exists(Context::$loadedContext));
+        }
+
+        // Restoring context.
+        Context::load('');
+    }
+
+    public function contextLoading()
+    {
+        return [
+            'MySQL match' => ['MySql50500', 'MySql50500'],
+            'MySQL strip' => ['MySql50712', 'MySql50700'],
+            'MySQL fallback' => ['MySql99999', 'MySql50700'],
+            'MariaDB match' => ['MariaDb100000', 'MariaDb100000'],
+            'MariaDB strip' => ['MariaDb109900', 'MariaDb100000'],
+            'MariaDB fallback' => ['MariaDb990000', 'MariaDb100300'],
+            'Invalid' => ['Sql', null],
+        ];
+    }
+
     /**
      * @dataProvider contextNames
      *