config: factor out exception_handler hook to a separate class

lib/pry.rb

@@ -21,6 +21,7 @@ require 'pry/syntax_highlighter'
 require 'pry/editor'
 require 'pry/history'
 require 'pry/color_printer'
+require 'pry/exception_handler'
 
 Pry::Commands = Pry::CommandSet.new unless defined?(Pry::Commands)
 

lib/pry/config.rb

@@ -7,7 +7,6 @@ class Pry
     # @return [Pry::Config]
     #   An object who implements the default configuration for all
     #   Pry sessions.
-    # rubocop:disable Metrics/AbcSize
     def self.defaults
       defaults = from_hash(
         input: Pry.lazy { lazy_readline(defaults) },
@@ -18,26 +17,7 @@ class Pry
         prompt_safe_contexts: Pry::Prompt::SAFE_CONTEXTS,
         print: Pry::ColorPrinter.method(:default),
         quiet: false,
-
-        # Will only show the first line of the backtrace
-        exception_handler: proc do |output, exception, _|
-          if exception.is_a?(UserError) && exception.is_a?(SyntaxError)
-            output.puts "SyntaxError: #{exception.message.sub(/.*syntax error, */m, '')}"
-          else
-            output.puts "#{exception.class}: #{exception.message}"
-            output.puts "from #{exception.backtrace.first}"
-
-            if exception.respond_to? :cause
-              cause = exception.cause
-              while cause
-                output.puts "Caused by #{cause.class}: #{cause}\n"
-                output.puts "from #{cause.backtrace.first}"
-                cause = cause.cause
-              end
-            end
-          end
-        end,
-
+        exception_handler: Pry::ExceptionHandler.method(:handle_exception),
         unrescued_exceptions: [
           ::SystemExit, ::SignalException, Pry::TooSafeException
         ],
@@ -113,7 +93,6 @@ class Pry
         exec_string: ""
       )
     end
-    # rubocop:enable Metrics/AbcSize
 
     def self.shortcuts
       Convenience::SHORTCUTS

lib/pry/exception_handler.rb

@@ -0,0 +1,41 @@
+class Pry
+  # @api private
+  # @since ?.?.?
+  module ExceptionHandler
+    class << self
+      # Will only show the first line of the backtrace.
+      def handle_exception(output, exception, _pry_instance)
+        if exception.is_a?(UserError) && exception.is_a?(SyntaxError)
+          output.puts "SyntaxError: #{exception.message.sub(/.*syntax error, */m, '')}"
+        else
+          output.puts standard_error_text_for(exception)
+        end
+      end
+
+      private
+
+      def standard_error_text_for(exception)
+        text = exception_text(exception)
+        return text unless exception.respond_to?(:cause)
+
+        cause = exception.cause
+        while cause
+          text += cause_text(cause)
+          cause = cause.cause
+        end
+
+        text
+      end
+
+      def exception_text(exception)
+        "#{exception.class}: #{exception.message}\n" \
+        "from #{exception.backtrace.first}\n"
+      end
+
+      def cause_text(cause)
+        "Caused by #{cause.class}: #{cause}\n" \
+        "from #{cause.backtrace.first}\n"
+      end
+    end
+  end
+end

spec/exception_handler_spec.rb

@@ -0,0 +1,64 @@
+RSpec.describe Pry::ExceptionHandler do
+  describe ".handle_exception" do
+    let(:output) { StringIO.new }
+    let(:pry_instance) { Pry.new }
+
+    context "when exception is a UserError and a SyntaxError" do
+      let(:exception) do
+        SyntaxError.new('cool syntax error, dude').extend(Pry::UserError)
+      end
+
+      it "prints the syntax error with customized message" do
+        described_class.handle_exception(output, exception, pry_instance)
+        expect(output.string).to start_with("SyntaxError: dude\n")
+      end
+    end
+
+    context "when exception is a standard error" do
+      let(:exception) do
+        error = StandardError.new('oops')
+        error.set_backtrace(["/bin/pry:23:in `<main>'"])
+        error
+      end
+
+      it "prints standard error message" do
+        described_class.handle_exception(output, exception, pry_instance)
+        expect(output.string)
+          .to eq("StandardError: oops\nfrom /bin/pry:23:in `<main>'\n")
+      end
+    end
+
+    context "when exception is a nested standard error" do
+      let(:exception) do
+        error = nil
+        begin
+          begin
+            raise 'nested oops'
+          rescue # rubocop:disable Style/RescueStandardError
+            raise 'outer oops'
+          end
+        rescue StandardError => outer_error
+          error = outer_error
+        end
+
+        error
+      end
+
+      before do
+        if RUBY_VERSION.start_with?('1.9', '2.0')
+          skip("Ruby #{RUBY_VERSION} doesn't support nested exceptions")
+        end
+      end
+
+      it "prints standard error message" do
+        described_class.handle_exception(output, exception, pry_instance)
+        expect(output.string).to match(
+          /RuntimeError:\souter\soops\n
+           from\s.+\n
+           Caused\sby\sRuntimeError:\snested\soops\n
+           from.+/x
+        )
+      end
+    end
+  end
+end