Render exception class PHPDoc description in HTML debug output

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 5.0.0 under development
 
+- Enh #104: Render exception class PHPDoc description with safe markdown links in HTML debug output (@dbuhonov)
 - Chg #162: Replace deprecated `ThrowableResponseFactory` class usage to new one, and remove it (@vjik)
 - Enh #163: Explicitly import classes, functions, and constants in "use" section (@mspirkov)
 - Bug #164: Fix missing items in stack trace HTML output when handling a PHP error (@vjik)

src/Renderer/HtmlRenderer.php

@@ -16,6 +16,7 @@
 use Yiisoft\ErrorHandler\ThrowableRendererInterface;
 use Yiisoft\FriendlyException\FriendlyExceptionInterface;
 use Yiisoft\Http\Header;
+use ReflectionClass;
 use ReflectionException;
 use ReflectionFunction;
 use ReflectionMethod;
@@ -45,15 +46,22 @@
 use function ob_implicit_flush;
 use function ob_start;
 use function realpath;
+use function preg_match;
+use function preg_replace;
+use function preg_replace_callback;
+use function preg_split;
 use function str_replace;
+use function str_starts_with;
 use function stripos;
 use function strlen;
 use function count;
 use function function_exists;
+use function trim;
 
 use const DIRECTORY_SEPARATOR;
 use const ENT_QUOTES;
 use const EXTR_OVERWRITE;
+use const PREG_SPLIT_DELIM_CAPTURE;
 
 /**
  * Formats throwable into HTML string.
@@ -204,10 +212,29 @@ public function render(Throwable $t, ?ServerRequestInterface $request = null): E
 
     public function renderVerbose(Throwable $t, ?ServerRequestInterface $request = null): ErrorData
     {
+        $solution = null;
+        $exceptionDescription = null;
+        $displayThrowable = $t;
+
+        if ($t instanceof CompositeException) {
+            $displayThrowable = $t->getFirstException();
+        }
+
+        if ($displayThrowable instanceof FriendlyExceptionInterface) {
+            $solution = $displayThrowable->getSolution();
+        } else {
+            $exceptionDescription = $this->getThrowableDescription($displayThrowable);
+        }
+
         return new ErrorData(
             $this->renderTemplate($this->verboseTemplate, [
                 'request' => $request,
                 'throwable' => $t,
+                'displayThrowable' => $displayThrowable,
+                'solution' => $solution,
+                'exceptionClass' => $displayThrowable::class,
+                'exceptionMessage' => $displayThrowable->getMessage(),
+                'exceptionDescription' => $exceptionDescription,
             ]),
             [Header::CONTENT_TYPE => self::CONTENT_TYPE],
         );
@@ -541,6 +568,111 @@ public function removeAnonymous(string $value): string
         return $anonymousPosition !== false ? substr($value, 0, $anonymousPosition) : $value;
     }
 
+    /**
+     * Extracts a user-facing description from throwable class PHPDoc.
+     *
+     * Takes only descriptive text before block tags, normalizes unsafe markup
+     * into safe markdown/plain text and converts it into an HTML fragment
+     * suitable for direct inclusion in the error template.
+     * Inline {@see ...}/{@link ...} annotations are rendered as markdown links.
+     *
+     * The returned value is an HTML snippet (for example, containing <p>, <a>,
+     * <code> elements) and is intended to be inserted into the template as-is,
+     * without additional HTML-escaping.
+     *
+     * @return string|null HTML fragment describing the throwable, or null if no description is available.
+     */
+    private function getThrowableDescription(Throwable $throwable): ?string
+    {
+        $docComment = (new ReflectionClass($throwable))->getDocComment();
+        if ($docComment === false) {
+            return null;
+        }
+
+        $descriptionLines = [];
+        foreach (preg_split('/\R/', $docComment) ?: [] as $line) {
+            $line = trim($line);
+            $line = preg_replace(
+                ['/^\/\*\*?/', '/\*\/$/', '/^\*\s?/'],
+                '',
+                $line,
+            ) ?? $line;
+            $line = trim($line);
+
+            if ($line !== '' && str_starts_with($line, '@')) {
+                break;
+            }
+
+            $descriptionLines[] = $line;
+        }
+
+        $description = trim(implode("\n", $descriptionLines));
+        if ($description === '') {
+            return null;
+        }
+
+        $description = preg_replace_callback(
+            '/\{@(?:see|link)\s+(?<target>[^\s}]+)(?:\s+(?<label>[^}]+))?}/i',
+            static function (array $matches): string {
+                $target = $matches['target'];
+                $label = trim($matches['label'] ?? '');
+
+                if (preg_match('/^https?:\/\//i', $target) === 1) {
+                    $text = $label !== '' ? $label : $target;
+                    return '[' . $text . '](' . $target . ')';
+                }
+
+                if ($label !== '') {
+                    return $label . ' (`' . $target . '`)';
+                }
+
+                return '`' . $target . '`';
+            },
+            $description,
+        ) ?? $description;
+
+        $tokenPattern = '/^(?:`(?<code>[^`]+)`|(?<image>!)?\[(?<label>[^\]]+)]\((?<target>[^)]+)\))$/';
+        $parts = preg_split(
+            '/(!?\[[^]]+]\([^)]+\)|`[^`]+`)/',
+            $description,
+            -1,
+            PREG_SPLIT_DELIM_CAPTURE,
+        ) ?: [];
+
+        $normalized = [];
+
+        foreach ($parts as $part) {
+            if ($part === '') {
+                continue;
+            }
+
+            if (preg_match($tokenPattern, $part, $matches) !== 1) {
+                $normalized[] = $this->htmlEncode($part);
+                continue;
+            }
+
+            if (($matches['code'] ?? '') !== '') {
+                $normalized[] = '<code>' . $this->htmlEncode($matches['code']) . '</code>';
+                continue;
+            }
+
+            $label = $this->htmlEncode($matches['label']);
+            $target = $matches['target'];
+            $imageMarker = $matches['image'] ?? '';
+
+            if ($imageMarker === '' && preg_match('/^https?:\/\//i', $target) === 1) {
+                $normalized[] = '[' . $label . '](' . $target . ')';
+                continue;
+            }
+
+            $normalized[] = $imageMarker . $label . ' (<code>' . $this->htmlEncode($target) . '</code>)';
+        }
+
+        $normalized = trim(implode('', $normalized));
+
+        return $this->parseMarkdown($normalized);
+    }
+
     /**
      * Renders a template.
      *

templates/development.php

@@ -1,26 +1,22 @@
 <?php
 
 use Psr\Http\Message\ServerRequestInterface;
-use Yiisoft\ErrorHandler\CompositeException;
 use Yiisoft\ErrorHandler\Exception\ErrorException;
 use Yiisoft\ErrorHandler\Renderer\HtmlRenderer;
 use Yiisoft\FriendlyException\FriendlyExceptionInterface;
 
 /**
  * @var ServerRequestInterface|null $request
  * @var Throwable $throwable
+ * @var Throwable $displayThrowable
+ * @var string|null $solution
+ * @var string $exceptionClass
+ * @var string $exceptionMessage
+ * @var string|null $exceptionDescription
  */
 
 $theme = $_COOKIE['yii-exception-theme'] ?? '';
 
-$originalException = $throwable;
-if ($throwable instanceof CompositeException) {
-    $throwable = $throwable->getFirstException();
-}
-$solution = $throwable instanceof FriendlyExceptionInterface ? $throwable->getSolution() : null;
-$exceptionClass = get_class($throwable);
-$exceptionMessage = $throwable->getMessage();
-
 /**
  * @var HtmlRenderer $this
  */
@@ -32,7 +28,7 @@
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <title>
-        <?= $this->htmlEncode($this->getThrowableName($throwable)) ?>
+        <?= $this->htmlEncode($this->getThrowableName($displayThrowable)) ?>
     </title>
     <style>
         <?= file_get_contents(__DIR__ . '/development.css') ?>
@@ -79,25 +75,29 @@
     <div class="exception-card">
         <div class="exception-class">
             <?php
-            if ($throwable instanceof FriendlyExceptionInterface): ?>
-                <span><?= $this->htmlEncode($throwable->getName())?></span>
+            if ($displayThrowable instanceof FriendlyExceptionInterface): ?>
+                <span><?= $this->htmlEncode($displayThrowable->getName())?></span>
                 &mdash;
                 <?= $exceptionClass ?>
             <?php else: ?>
                 <span><?= $exceptionClass ?></span>
             <?php endif ?>
-            (Code #<?= $throwable->getCode() ?>)
+            (Code #<?= $displayThrowable->getCode() ?>)
         </div>
 
         <div class="exception-message">
             <?= nl2br($this->htmlEncode($exceptionMessage)) ?>
         </div>
 
+        <?php if ($exceptionDescription !== null): ?>
+            <div class="exception-description solution"><?= $exceptionDescription ?></div>
+        <?php endif ?>
+
         <?php if ($solution !== null): ?>
             <div class="solution"><?= $this->parseMarkdown($solution) ?></div>
         <?php endif ?>
 
-        <?= $this->renderPreviousExceptions($originalException) ?>
+        <?= $this->renderPreviousExceptions($throwable) ?>
 
         <textarea id="clipboard"><?= $this->htmlEncode((string) $throwable) ?></textarea>
         <span id="copied">Copied!</span>
@@ -117,10 +117,10 @@ class="copy-clipboard"
 <main>
     <div class="call-stack">
         <?= $this->renderCallStack(
-            $throwable,
-            $originalException === $throwable && $originalException instanceof ErrorException
-                ? $originalException->getBacktrace()
-                : $throwable->getTrace()
+            $displayThrowable,
+            $displayThrowable === $throwable && $throwable instanceof ErrorException
+                ? $throwable->getBacktrace()
+                : $displayThrowable->getTrace(),
         ) ?>
     </div>
     <?php if ($request && ($requestInfo = $this->renderRequest($request)) !== ''): ?>