MDL-79974 core: Add Whoops when debugging

Whoops will only be used under the following conditions:

- Not an AJAX request
- Not a CLI usage
- debugdisplay is set
- composer dependencies are installed
- Whoops is available
- The configuration setting is enabled

composer.json

@@ -14,7 +14,8 @@
         "symfony/http-client": "^4.4 || ^5.0 || ^6.0",
         "symfony/mime": "^4.4 || ^5.0 || ^6.0",
         "behat/behat": "3.13.*",
-        "oleg-andreyev/mink-phpwebdriver": "1.2.*"
+        "oleg-andreyev/mink-phpwebdriver": "1.2.*",
+        "filp/whoops": "^2.15"
     },
     "autoload-dev": {
         "psr-0": {

config-dist.php

@@ -780,6 +780,23 @@
 // $CFG->debug = (E_ALL | E_STRICT);   // === DEBUG_DEVELOPER - NOT FOR PRODUCTION SERVERS!
 // $CFG->debugdisplay = 1;             // NOT FOR PRODUCTION SERVERS!
 //
+// Display exceptions using the 'pretty' Whoops! utility.
+// This is only used when the following conditions are met:
+// - Composer dependencies are installed
+// - $CFG->debug and $CFG->debugdisplay are set
+// - the request is not a CLI, or AJAX request
+//
+// To further control this, the debug_developer_use_pretty_exceptions setting can be set to false.
+// $CFG->debug_developer_use_pretty_exceptions = true;
+//
+// The Whoops! UI can also provide a link to open files in  your preferred editor.
+// You can set your preferred editor by setting:
+// $CFG->debug_developer_editor = 'vscode';
+//
+// See https://github.com/filp/whoops/blob/master/docs/Open%20Files%20In%20An%20Editor.md for more information on
+// supported editors.
+// If your editor is not listed you can provide a callback as documented.
+//
 // You can specify a comma separated list of user ids that that always see
 // debug messages, this overrides the debug flag in $CFG->debug and $CFG->debugdisplay
 // for these users only.

lib/setup.php

@@ -706,6 +706,12 @@
 }
 $CFG->debugdeveloper = (($CFG->debug & DEBUG_DEVELOPER) === DEBUG_DEVELOPER);
 
+// Set a default value for whether to show exceptions in a pretty format.
+if (!property_exists($CFG, 'debug_developer_use_pretty_exceptions')) {
+    $CFG->debug_developer_use_pretty_exceptions = true;
+
+}
+
 // Find out if PHP configured to display warnings,
 // this is a security problem because some moodle scripts may
 // disclose sensitive information.

lib/setuplib.php

@@ -343,6 +343,67 @@ function __construct($debuginfo = NULL) {
     }
 }
 
+/**
+ * Get the Whoops! handler.
+ *
+ * @return \Whoops\Run|null
+ */
+function get_whoops(): ?\Whoops\Run {
+    global $CFG;
+
+    if (CLI_SCRIPT || AJAX_SCRIPT) {
+        return null;
+    }
+
+    if (defined('PHPUNIT_TEST') && PHPUNIT_TEST) {
+        return null;
+    }
+
+    if (defined('BEHAT_TEST') && BEHAT_TEST) {
+        return null;
+    }
+
+    if (!$CFG->debugdisplay) {
+        return null;
+    }
+
+    if (!$CFG->debug_developer_use_pretty_exceptions) {
+        return null;
+    }
+
+    $composerautoload = "{$CFG->dirroot}/vendor/autoload.php";
+    if (file_exists($composerautoload)) {
+        require_once($composerautoload);
+    }
+
+    if (!class_exists(\Whoops\Run::class)) {
+        return null;
+    }
+
+    // We have Whoops available, use it.
+    $whoops = new \Whoops\Run();
+
+    // Append a custom handler to add some more information to the frames.
+    $whoops->appendHandler(function ($exception, $inspector, $run) {
+        // Moodle exceptions often have a link to the Moodle docs pages for them.
+        // Add that to the first frame in the stack.
+        $info = get_exception_info($exception);
+        if ($info->moreinfourl) {
+            $collection = $inspector->getFrames();
+            $collection[0]->addComment("{$info->moreinfourl}", 'More info');
+        }
+    });
+
+    // Add the Pretty page handler. It's the bee's knees.
+    $handler = new \Whoops\Handler\PrettyPageHandler();
+    if (isset($CFG->debug_developer_editor)) {
+        $handler->setEditor($CFG->debug_developer_editor ?: null);
+    }
+    $whoops->appendHandler($handler);
+
+    return $whoops;
+}
+
 /**
  * Default exception handler.
  *
@@ -366,6 +427,11 @@ function default_exception_handler($ex) {
     // should be either empty or the length of the error page.
     @header_remove('Content-Length');
 
+    if ($whoops = get_whoops()) {
+        // If whoops is available we will use it. The get_whoops() function checks whether all conditions are met.
+        $whoops->handleException($ex);
+    }
+
     if (is_early_init($info->backtrace)) {
         echo bootstrap_renderer::early_error($info->message, $info->moreinfourl, $info->link, $info->backtrace, $info->debuginfo, $info->errorcode);
     } else {
@@ -422,6 +488,10 @@ function default_exception_handler($ex) {
  * @return bool false means use default error handler
  */
 function default_error_handler($errno, $errstr, $errfile, $errline) {
+    if ($whoops = get_whoops()) {
+        // If whoops is available we will use it. The get_whoops() function checks whether all conditions are met.
+        $whoops->handleError($errno, $errstr, $errfile, $errline);
+    }
     if ($errno == 4096) {
         //fatal catchable error
         throw new coding_exception('PHP catchable fatal error', $errstr);