From 1bca6cbc29d57dda859323826fa9e534fc461700 Mon Sep 17 00:00:00 2001
From: Julien Portalier <julien@portalier.com>
Date: Fri, 25 Apr 2025 09:57:58 +0200
Subject: [PATCH] Workaround for #15705: slow compilation of
 `Crystal.bufferer_message`

Inlines the inspect of exceptions into the `Crystal.buffered_message`
method to avoid call(s) to `Exception#inspect_with_backtrace(IO)` that
causes a dramatic impact on performance when compiling the crystal
compiler (and potentially other applications).
---
 src/crystal/print_buffered.cr | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/crystal/print_buffered.cr b/src/crystal/print_buffered.cr
index e58423f0f08b..5208394c83a6 100644
--- a/src/crystal/print_buffered.cr
+++ b/src/crystal/print_buffered.cr
@@ -31,7 +31,29 @@ module Crystal
 
     if exception
       buf << ": "
-      exception.inspect_with_backtrace(buf)
+
+      # FIXME: calling `Exception#inspect_with_backtrace` sometimes dramatically
+      # slows down compilation times, we thus manually print the backtrace
+      # instead of calling the method.
+      #
+      # See https://github.com/crystal-lang/crystal/issues/15705
+      #
+      # exception.inspect_with_backtrace(buf)
+      loop do
+        buf << exception.message << " (" << exception.class << ")\n"
+
+        if backtrace = exception.backtrace?
+          backtrace.each { |line| buf << "  from " << line << '\n' }
+        end
+
+        if ex = exception.@cause
+          buf << "Caused by: "
+          exception = ex
+          next
+        end
+
+        break
+      end
     else
       buf.puts
       backtrace.try(&.each { |line| buf << "  from " << line << '\n' })