[12.x] Display previous exceptions in error renderer

[imhayatunnabi]

Summary

• Adds display of previous exceptions in the exception renderer
• Shows exception chains in a collapsible section similar to the trace
• Includes previous exceptions in markdown export
• Fully addresses issue Exception render does not expose previous exceptions #57366

Problem

When exceptions are wrapped with previous exceptions using the $previous parameter, the error page only shows the top-level exception. This makes debugging difficult as developers cannot see the full exception chain without diving into code, turning a simple one-minute debug into an hour-long investigation.

As requested in #57366:

"When the exception is rendered by Laravel as a response, there is no way to know the previous exception or track the previous exceptions from there."

Solution

1. Exception Chain Traversal (Exception.php:277-301)

Added two new methods to the Exception class:

• previousExceptions() - Traverses the entire exception chain using $exception->getPrevious() until it returns null, collecting class, message, and code for each
• hasPreviousExceptions() - Checks if any previous exceptions exist

2. New UI Component (previous-exceptions.blade.php)

Created a new Blade component that displays all previous exceptions in a section styled like the Exception Trace:

• Shows exception class name (monospaced font)
• Displays exception message
• Shows exception code when present
• Numbered badges (ReflectionException #1, Fix Fatal error on Class 'Illuminate\Filesystem' load #2, etc.) to indicate order in the chain
• Only renders when previous exceptions exist

3. Template Integration

• Updated show.blade.php to include the previous exceptions section between trace and queries
• Updated markdown.blade.php to include previous exceptions in markdown exports for sharing/documentation

4. Test Coverage

Added testItCanRenderPreviousExceptions() that verifies:

• A chain of 3 nested exceptions is properly rendered
• All exception messages appear in the output
• The "Previous exceptions" section header is displayed

Test Plan

• Added test for rendering exception chains with 3 nested exceptions
• All existing renderer tests pass (8/8 tests)
• Verified traversal works until getPrevious() returns null
• Confirmed UI matches Exception Trace styling
• Verified previous exceptions included in markdown export

What This Fixes

Resolves #57366 - Exceptions rendering do not expose previous exceptions