Toggle deprecation warnings on error level.

By using the error level to control deprecation warnings, we allow users
to have them enabled in production but go into log files. This is useful
for ensuring all the deprecation warnings have been caught/fixed.

Author: markstory

src/Core/functions.php

@@ -260,7 +260,7 @@ function env($key, $default = null)
      */
     function deprecationWarning($message, $stackFrame = 2)
     {
-        if (!Configure::read('debug')) {
+        if (!(error_reporting() & E_USER_DEPRECATED)) {
             return;
         }
         $trace = debug_backtrace();

tests/TestCase/Core/FunctionsTest.php

@@ -14,7 +14,6 @@
  */
 namespace Cake\Test\TestCase\Core;
 
-use Cake\Core\Configure;
 use Cake\TestSuite\TestCase;
 
 /**
@@ -50,9 +49,8 @@ public function testEnv()
      * @expectedException PHPUnit\Framework\Error\Deprecated
      * @expectedExceptionMessage This is going away - [internal], line: ??
      */
-    public function testDeprecationWarningDebugEnabled()
+    public function testDeprecationWarningEnabled()
     {
-        Configure::write('debug', true);
         error_reporting(E_ALL);
         deprecationWarning('This is going away', 1);
     }
@@ -63,9 +61,8 @@ public function testDeprecationWarningDebugEnabled()
      * @expectedException PHPUnit\Framework\Error\Deprecated
      * @expectedExceptionMessageRegExp /This is going away - (.*?)\/TestCase.php, line\: \d+/
      */
-    public function testDeprecationWarningDebugEnabledDefaultFrame()
+    public function testDeprecationWarningEnabledDefaultFrame()
     {
-        Configure::write('debug', true);
         error_reporting(E_ALL);
         deprecationWarning('This is going away');
     }
@@ -75,10 +72,9 @@ public function testDeprecationWarningDebugEnabledDefaultFrame()
      *
      * @return void
      */
-    public function testDeprecationWarningDebugDisabled()
+    public function testDeprecationWarningLevelDisabled()
     {
-        Configure::write('debug', false);
-        error_reporting(E_ALL);
+        error_reporting(E_ALL ^ E_USER_DEPRECATED);
         $this->assertNull(deprecationWarning('This is going away'));
     }
 }