Support IRB.conf[:BACKTRACE_FILTER]`

This config allows users to customize the backtrace of exceptions raised
and displayed in IRB sessions. This is useful for filtering out library
frames from the backtrace.

IRB expects the given value to response to `filter` method and return
the filtered backtrace.

lib/irb.rb

@@ -1222,27 +1222,33 @@ def handle_exception(exc)
         irb_bug = true
       else
         irb_bug = false
-        # This is mostly to make IRB work nicely with Rails console's backtrace filtering, which patches WorkSpace#filter_backtrace
-        # In such use case, we want to filter the exception's backtrace before its displayed through Exception#full_message
-        # And we clone the exception object in order to avoid mutating the original exception
-        # TODO: introduce better API to expose exception backtrace externally
-        backtrace = exc.backtrace.map { |l| @context.workspace.filter_backtrace(l) }.compact
+        # To support backtrace filtering while utilizing Exception#full_message, we need to clone
+        # the exception to avoid modifying the original exception's backtrace.
         exc = exc.clone
-        exc.set_backtrace(backtrace)
-      end
+        filtered_backtrace = exc.backtrace.map { |l| @context.workspace.filter_backtrace(l) }.compact
+        backtrace_filter = IRB.conf[:BACKTRACE_FILTER]
 
-      if RUBY_VERSION < '3.0.0'
-        if STDOUT.tty?
-          message = exc.full_message(order: :bottom)
-          order = :bottom
-        else
-          message = exc.full_message(order: :top)
-          order = :top
+        if backtrace_filter
+          if backtrace_filter.respond_to?(:filter)
+            filtered_backtrace = backtrace_filter.filter(filtered_backtrace)
+          else
+            warn "IRB.conf[:BACKTRACE_FILTER] #{backtrace_filter} should respond to `filter` method"
+          end
         end
-      else # '3.0.0' <= RUBY_VERSION
-        message = exc.full_message(order: :top)
-        order = :top
+
+        exc.set_backtrace(filtered_backtrace)
       end
+
+      highlight = Color.colorable?
+
+      order =
+        if RUBY_VERSION < '3.0.0'
+          STDOUT.tty? ? :bottom : :top
+        else # '3.0.0' <= RUBY_VERSION
+          :top
+        end
+
+      message = exc.full_message(order: order, highlight: highlight)
       message = convert_invalid_byte_sequence(message, exc.message.encoding)
       message = encode_with_invalid_byte_sequence(message, IRB.conf[:LC_MESSAGES].encoding) unless message.encoding.to_s.casecmp?(IRB.conf[:LC_MESSAGES].encoding.to_s)
       message = message.gsub(/((?:^\t.+$\n)+)/) { |m|

test/irb/test_irb.rb

@@ -753,4 +753,91 @@ def build_irb
       IRB::Irb.new(workspace, TestInputMethod.new)
     end
   end
+
+  class BacktraceFilteringTest < TestIRB::IntegrationTestCase
+    def test_backtrace_filtering
+      write_ruby <<~'RUBY'
+        def foo
+          raise "error"
+        end
+
+        def bar
+          foo
+        end
+
+        binding.irb
+      RUBY
+
+      output = run_ruby_file do
+        type "bar"
+        type "exit"
+      end
+
+      assert_match(/irbtest-.*\.rb:2:in (`|'Object#)foo': error \(RuntimeError\)/, output)
+      frame_traces = output.split("\n").select { |line| line.strip.start_with?(/from /) }.map(&:strip)
+
+      expected_traces = if RUBY_VERSION >= "3.3.0"
+        [
+          /from .*\/irbtest-.*.rb:6:in (`|'Object#)bar'/,
+          /from .*\/irbtest-.*.rb\(irb\):1:in [`']<main>'/,
+          /from <internal:kernel>:\d+:in (`|'Kernel#)loop'/,
+          /from <internal:prelude>:\d+:in (`|'Binding#)irb'/,
+          /from .*\/irbtest-.*.rb:9:in [`']<main>'/
+        ]
+      else
+        [
+          /from .*\/irbtest-.*.rb:6:in (`|'Object#)bar'/,
+          /from .*\/irbtest-.*.rb\(irb\):1:in [`']<main>'/,
+          /from <internal:prelude>:\d+:in (`|'Binding#)irb'/,
+          /from .*\/irbtest-.*.rb:9:in [`']<main>'/
+        ]
+      end
+
+      expected_traces.each_with_index do |expected_trace, index|
+        assert_match(expected_trace, frame_traces[index])
+      end
+    end
+
+    def test_backtrace_filtering_with_backtrace_filter
+      write_rc <<~'RUBY'
+        class TestBacktraceFilter
+          def self.filter(backtrace)
+            backtrace.reject { |line| line.include?("internal") }
+          end
+        end
+
+        IRB.conf[:BACKTRACE_FILTER] = TestBacktraceFilter
+      RUBY
+
+      write_ruby <<~'RUBY'
+        def foo
+          raise "error"
+        end
+
+        def bar
+          foo
+        end
+
+        binding.irb
+      RUBY
+
+      output = run_ruby_file do
+        type "bar"
+        type "exit"
+      end
+
+      assert_match(/irbtest-.*\.rb:2:in (`|'Object#)foo': error \(RuntimeError\)/, output)
+      frame_traces = output.split("\n").select { |line| line.strip.start_with?(/from /) }.map(&:strip)
+
+      expected_traces = [
+        /from .*\/irbtest-.*.rb:6:in (`|'Object#)bar'/,
+        /from .*\/irbtest-.*.rb\(irb\):1:in [`']<main>'/,
+        /from .*\/irbtest-.*.rb:9:in [`']<main>'/
+      ]
+
+      expected_traces.each_with_index do |expected_trace, index|
+        assert_match(expected_trace, frame_traces[index])
+      end
+    end
+  end
 end