Throw MalformedRegex for malformed regex pattern

ReadMe.md

@@ -19,6 +19,7 @@ extracted from [T-Regx](https://github.com/T-Regx/T-Regx) library, waste removed
 
 ## Examples
 
+Testing string subject against regex pattern:
 ```php
 re_test('[a-z]+', 'word');
 // bool (true)
@@ -28,3 +29,12 @@ re_test('[a-z]+', 'word');
 re_test('[a-z]+', 'WORD', modifiers:'i');
 // bool (true)
 ```
+
+Helpful error message for syntax errors in regex patterns:
+```php
+try {
+    re_test('[a-z', 'word');
+} catch (\Regex\MalformedRegex $exception) {
+    // 'missing terminating ] for character class'
+}
+```

composer.json

@@ -1,5 +1,8 @@
 {
   "autoload": {
+    "psr-4": {
+      "Regex\\": "src/Regex/"
+    },
     "files": [
       "src/functions.php"
     ]

src/Regex/MalformedRegex.php

@@ -0,0 +1,4 @@
+<?php
+namespace Regex;
+
+class MalformedRegex extends \RuntimeException {}

src/functions.php

@@ -1,5 +1,16 @@
 <?php
 
+use Regex\MalformedRegex;
+
 function re_test(string $pattern, string $subject, string $modifiers = null): bool {
-    return \preg_match("/$pattern/$modifiers", $subject);
+    $pregMatch = \preg_match("/$pattern/$modifiers", $subject);
+    $error = \error_get_last();
+    if ($error) {
+        $message = $error['message'];
+        $prefix = 'preg_match(): Compilation failed: ';
+        if (str_starts_with($message, $prefix)) {
+            throw new MalformedRegex(\subStr($message, \strLen($prefix)));
+        }
+    }
+    return $pregMatch;
 }

test/FunctionsTest.php

@@ -3,6 +3,7 @@
 
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
+use Regex\MalformedRegex;
 
 class FunctionsTest extends TestCase
 {
@@ -20,4 +21,16 @@ public function unmatchedSubject_testsFalse() {
     public function matchingCaseInsensitive_testsTrue() {
         $this->assertTrue(re_test('[a-z]', 'WORD', modifiers:'i'));
     }
+
+    #[Test]
+    public function malformedPatternException(): void {
+        $this->expectException(MalformedRegex::class);
+        re_test('[a-z', 'word');
+    }
+
+    #[Test]
+    public function malformedPatternExceptionMessage(): void {
+        $this->expectExceptionMessage('missing terminating ] for character class');
+        re_test('[a-z', 'word');
+    }
 }