Improve error message

Author: markus-moser

src/QueryLanguage/Pql/Parser.php

@@ -175,7 +175,13 @@ private function parseComparison(array &$subQueries): array|ParseResultSubQuery
         $this->validateCurrentTokenNotEmpty();
 
         if (!$this->currentToken() || !$this->currentToken()->isA(...self::FIELD_NAME_TOKENS)) {
-            $this->throwParsingException('a field name', '`' . ($this->currentToken()['value'] ?? 'null') . '`');
+            $tokenValue = $this->currentToken()['value'] ?? 'null';
+            $message = null;
+            if (in_arrayi($tokenValue, ['like', 'not like', 'null', 'empty'])) {
+                $message = sprintf('Expected %s, found %s.', 'a field name', '`' . $tokenValue . '`')
+                    . ' Reserved keywords cannot be used as field name.';
+            }
+            $this->throwParsingException('a field name', '`' . $tokenValue . '`', $message);
         }
 
         /** @var Token $fieldToken */

tests/Unit/QueryLanguage/Pql/ParserTest.php

@@ -494,14 +494,14 @@ public function testParseError9(): void
     public function testParseError10(): void
     {
         $this->expectException(ParsingException::class);
-        $this->expectExceptionMessage('Expected a field name, found `null`');
+        $this->expectExceptionMessage('Expected a field name, found `null`. Reserved keywords cannot be used as field name.');
         $this->parseQuery('color="red" or null = "foo"');
     }
 
     public function testParseError11(): void
     {
         $this->expectException(ParsingException::class);
-        $this->expectExceptionMessage('Expected a field name, found `like`');
+        $this->expectExceptionMessage('Expected a field name, found `like`. Reserved keywords cannot be used as field name.');
         $this->parseQuery('color="red" or like = "foo"');
     }