Introduce RegexSyntaxValidator

composer.json

@@ -5,7 +5,7 @@
   "homepage": "https://github.com/Icinga/ipl-validator",
   "license": "MIT",
   "require": {
-    "php": ">=7.2",
+    "php": ">=8.0",
     "ext-mbstring": "*",
     "ext-openssl": "*",
     "ipl/stdlib": ">=0.12.0",

src/RegexSyntaxValidator.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace ipl\Validator;
+
+/**
+ * Validate a PHP regular expression, syntax: /PATTERN/MODIFIERS
+ */
+class RegexSyntaxValidator extends BaseValidator
+{
+    /**
+     * @param string $value
+     *
+     * @return bool
+     */
+    public function isValid($value): bool
+    {
+        $this->clearMessages();
+
+        if (! is_string($value)) {
+            $this->addMessage($this->translate('Invalid regex given, must be a string'));
+
+            return false;
+        }
+
+        if (@preg_match($value, '') === false) {
+            $this->addMessage(sprintf(
+                $this->translate('Regex "%s" failed to compile: %s'),
+                $value,
+                preg_last_error_msg()
+            ));
+
+            return false;
+        }
+
+        return true;
+    }
+}

tests/RegexSyntaxValidatorTest.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace ipl\Tests\Validator;
+
+use ipl\I18n\NoopTranslator;
+use ipl\I18n\StaticTranslator;
+use ipl\Validator\RegexSyntaxValidator;
+
+class RegexSyntaxValidatorTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        StaticTranslator::$instance = new NoopTranslator();
+    }
+
+    public function testBadType()
+    {
+        $validator = new RegexSyntaxValidator();
+
+        $this->assertFalse($validator->isValid(null));
+        $this->assertFalse($validator->isValid(false));
+        $this->assertFalse($validator->isValid(true));
+        $this->assertFalse($validator->isValid(42));
+        $this->assertFalse($validator->isValid(3.14));
+        $this->assertFalse($validator->isValid([]));
+        $this->assertFalse($validator->isValid((object) []));
+    }
+
+    public function testInvalidRegex()
+    {
+        $validator = new RegexSyntaxValidator();
+
+        $this->assertFalse($validator->isValid('no_delimiters'));
+        $this->assertFalse($validator->isValid('/unclosed_pattern'));
+        $this->assertFalse($validator->isValid('/pattern/invalid-modifier!'));
+        $this->assertFalse($validator->isValid('/invalid[pattern/'));
+        $this->assertFalse($validator->isValid('/(unbalanced_parentheses/'));
+    }
+
+    public function testValidRegex()
+    {
+        $validator = new RegexSyntaxValidator();
+
+        $this->assertTrue($validator->isValid('/simple_pattern/'));
+        $this->assertTrue($validator->isValid('/pattern_with_modifiers/i'));
+        $this->assertTrue($validator->isValid('/complex[pattern](with){various}+elements?$/m'));
+    }
+}