feat: Opt-in logging of deprecations

app/Config/Exceptions.php

@@ -3,6 +3,7 @@
 namespace Config;
 
 use CodeIgniter\Config\BaseConfig;
+use Psr\Log\LogLevel;
 
 /**
  * Setup how the exception handler works.
@@ -49,4 +50,28 @@ class Exceptions extends BaseConfig
      * ex. ['server', 'setup/password', 'secret_token']
      */
     public array $sensitiveDataInTrace = [];
+
+    /**
+     * --------------------------------------------------------------------------
+     * LOG DEPRECATIONS INSTEAD OF THROWING?
+     * --------------------------------------------------------------------------
+     * By default, CodeIgniter converts deprecations into exceptions. Also,
+     * starting in PHP 8.1 will cause a lot of deprecated usage warnings.
+     * Use this option to temporarily cease the warnings and instead log those.
+     * This option also works for user deprecations.
+     */
+    public bool $logDeprecationsOnly = false;
+
+    /**
+     * --------------------------------------------------------------------------
+     * LOG LEVEL THRESHOLD FOR DEPRECATIONS
+     * --------------------------------------------------------------------------
+     * If `$logDeprecationsOnly` is set to `true`, this sets the log level
+     * to which the deprecation will be logged. This should be one of the log
+     * levels recognized by PSR-3.
+     *
+     * The related `Config\Logger::$threshold` should be adjusted, if needed,
+     * to capture logging the deprecations.
+     */
+    public string $deprecationLogLevel = LogLevel::WARNING;
 }

system/Debug/Exceptions.php

@@ -22,6 +22,7 @@
 use Config\Exceptions as ExceptionsConfig;
 use Config\Paths;
 use ErrorException;
+use Psr\Log\LogLevel;
 use Throwable;
 
 /**
@@ -82,6 +83,10 @@ public function __construct(ExceptionsConfig $config, $request, ResponseInterfac
         if (! isset($this->config->sensitiveDataInTrace)) {
             $this->config->sensitiveDataInTrace = [];
         }
+        if (! isset($this->config->logDeprecationsOnly, $this->config->deprecationLogLevel)) {
+            $this->config->logDeprecationsOnly = false;
+            $this->config->deprecationLogLevel = LogLevel::WARNING;
+        }
     }
 
     /**
@@ -155,6 +160,10 @@ public function exceptionHandler(Throwable $exception)
      */
     public function errorHandler(int $severity, string $message, ?string $file = null, ?int $line = null)
     {
+        if ($this->isDeprecationError($severity) && $this->config->logDeprecationsOnly) {
+            return $this->handleDeprecationError($message, $file, $line);
+        }
+
         if (! (error_reporting() & $severity)) {
             return;
         }
@@ -328,6 +337,35 @@ protected function determineCodes(Throwable $exception): array
         return [$statusCode, $exitStatus];
     }
 
+    private function isDeprecationError(int $error): bool
+    {
+        $deprecations = E_DEPRECATED | E_USER_DEPRECATED;
+
+        return ($error & $deprecations) !== 0;
+    }
+
+    /**
+     * @return true
+     */
+    private function handleDeprecationError(string $message, ?string $file = null, ?int $line = null): bool
+    {
+        // Remove the trace of the error handler.
+        $trace = array_slice(debug_backtrace(), 2);
+
+        log_message(
+            $this->config->deprecationLogLevel,
+            "[DEPRECATED] {message} in {errFile} on line {errLine}.\n{trace}",
+            [
+                'message' => $message,
+                'errFile' => clean_path($file ?? ''),
+                'errLine' => $line ?? 0,
+                'trace'   => self::renderBacktrace($trace),
+            ]
+        );
+
+        return true;
+    }
+
     // --------------------------------------------------------------------
     // Display Methods
     // --------------------------------------------------------------------

tests/system/Debug/ExceptionsTest.php

@@ -19,6 +19,7 @@
 use CodeIgniter\Test\ReflectionHelper;
 use Config\Exceptions as ExceptionsConfig;
 use Config\Services;
+use ErrorException;
 use RuntimeException;
 
 /**
@@ -32,9 +33,55 @@ final class ExceptionsTest extends CIUnitTestCase
 
     protected function setUp(): void
     {
+        parent::setUp();
+
         $this->exception = new Exceptions(new ExceptionsConfig(), Services::request(), Services::response());
     }
 
+    /**
+     * @requires PHP >= 8.1
+     */
+    public function testDeprecationsDoNotThrow(): void
+    {
+        $config = new ExceptionsConfig();
+
+        $config->logDeprecationsOnly = true;
+        $config->deprecationLogLevel = 'error';
+
+        $this->exception = new Exceptions($config, Services::request(), Services::response());
+        $this->exception->initialize();
+
+        // this is only needed for IDEs not to complain that strlen does not accept explicit null
+        $maybeNull = PHP_VERSION_ID >= 80100 ? null : 'random string';
+
+        try {
+            strlen($maybeNull);
+            $this->assertLogContains('error', '[DEPRECATED] strlen(): ');
+        } catch (ErrorException $e) {
+            $this->fail('The catch block should not be reached.');
+        } finally {
+            restore_error_handler();
+            restore_exception_handler();
+        }
+    }
+
+    public function testSuppressedDeprecationsDoNotThrow(): void
+    {
+        $config = new ExceptionsConfig();
+
+        $config->logDeprecationsOnly = true;
+        $config->deprecationLogLevel = 'error';
+
+        $this->exception = new Exceptions($config, Services::request(), Services::response());
+        $this->exception->initialize();
+
+        @trigger_error('Hello! I am a deprecation!', E_USER_DEPRECATED);
+        $this->assertLogContains('error', '[DEPRECATED] Hello! I am a deprecation!', false);
+
+        restore_error_handler();
+        restore_exception_handler();
+    }
+
     public function testDetermineViews(): void
     {
         $determineView = $this->getPrivateMethodInvoker($this->exception, 'determineView');