From 5056859ea8de7ab2920b628982764d246d81f827 Mon Sep 17 00:00:00 2001
From: TSUYUSATO Kitsune <make.just.on@gmail.com>
Date: Wed, 4 Apr 2018 02:33:07 +0900
Subject: [PATCH] Pass an unhandled exception to at_exit block as second
 argument (#5906)

* Pass an unhandled exception to at_exit block as second argument

Follow up #1921

It is better in some ways:

  - it does not need a new exception like `SystemExit`.
  - it does not break compatibility in most cases because block fill up lacking arguments.

* Add documentation for at_exit block arguments

* Update `at_exit` block arguments description

https://github.com/crystal-lang/crystal/pull/5906#discussion_r178840967
Thank you @jhass.
---
 spec/std/kernel_spec.cr | 16 ++++++++++++++++
 src/kernel.cr           | 12 +++++++++---
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/spec/std/kernel_spec.cr b/spec/std/kernel_spec.cr
index 04a6aa28d666..95f4eac96692 100644
--- a/spec/std/kernel_spec.cr
+++ b/spec/std/kernel_spec.cr
@@ -225,4 +225,20 @@ describe "at_exit" do
                            Unhandled exception: Kaboom!
                            OUTPUT
   end
+
+  it "can get unhandled exception in at_exit handler" do
+    status, _, error = build_and_run <<-CODE
+      at_exit do |_, ex|
+        STDERR.puts ex.try &.message
+      end
+
+      raise "Kaboom!"
+    CODE
+
+    status.success?.should be_false
+    error.should contain <<-OUTPUT
+                           Kaboom!
+                           Unhandled exception: Kaboom!
+                           OUTPUT
+  end
 end
diff --git a/src/kernel.cr b/src/kernel.cr
index 0bdc22637b50..78c0384adb0c 100644
--- a/src/kernel.cr
+++ b/src/kernel.cr
@@ -127,7 +127,7 @@ module AtExitHandlers
 
   class_property exception : Exception?
 
-  private class_getter(handlers) { [] of Int32 -> }
+  private class_getter(handlers) { [] of Int32, Exception? -> }
 
   def self.add(handler)
     raise "Cannot use at_exit from an at_exit handler" if @@running
@@ -142,7 +142,7 @@ module AtExitHandlers
       # Run the registered handlers in reverse order
       while handler = handlers.pop?
         begin
-          handler.call status
+          handler.call status, exception
         rescue handler_ex
           STDERR.puts "Error running at_exit handler: #{handler_ex}"
           status = 1 if status.zero?
@@ -180,7 +180,13 @@ end
 # ```text
 # goodbye cruel world
 # ```
-def at_exit(&handler : Int32 ->) : Nil
+#
+# The exit status code that will be returned by this program is passed to
+# the block as its first argument. In case of any unhandled exception, it is
+# passed as the second argument to the block, if the program terminates
+# normally or `exit(status)` is called explicitly, then the second argument
+# will be nil.
+def at_exit(&handler : Int32, Exception? ->) : Nil
   AtExitHandlers.add(handler)
 end