Add block variant of add_on_error

Usage:

  Bugsnag.on_error do |event|
    event.add_metadata(:info, { a: 1 })
  end

lib/bugsnag.rb

@@ -309,6 +309,20 @@ def leave_breadcrumb(name, meta_data={}, type=Bugsnag::Breadcrumbs::MANUAL_BREAD
       configuration.breadcrumbs << breadcrumb unless breadcrumb.ignore?
     end
 
+    ##
+    # Add the given block to the list of on_error callbacks
+    #
+    # The on_error callbacks will be called when an error is captured or reported
+    # and are passed a {Bugsnag::Report} object
+    #
+    # Returning false from an on_error callback will cause the error to be ignored
+    # and will prevent any remaining callbacks from being called
+    #
+    # @return [void]
+    def on_error(&block)
+      configuration.on_error(&block)
+    end
+
     ##
     # Add the given callback to the list of on_error callbacks
     #

lib/bugsnag/configuration.rb

@@ -569,6 +569,20 @@ def disable_sessions
       @enable_sessions = false
     end
 
+    ##
+    # Add the given block to the list of on_error callbacks
+    #
+    # The on_error callbacks will be called when an error is captured or reported
+    # and are passed a {Bugsnag::Report} object
+    #
+    # Returning false from an on_error callback will cause the error to be ignored
+    # and will prevent any remaining callbacks from being called
+    #
+    # @return [void]
+    def on_error(&block)
+      middleware.use(block)
+    end
+
     ##
     # Add the given callback to the list of on_error callbacks
     #

spec/on_error_spec.rb

@@ -18,13 +18,30 @@
     end)
   end
 
+  it "accepts a block" do
+    Bugsnag.on_error {|report| report.add_tab(:important, { hello: "world" }) }
+    Bugsnag.on_error {|report| report.add_tab(:significant, { hey: "earth" }) }
+
+    Bugsnag.notify(RuntimeError.new("Oh no!"))
+
+    expect(Bugsnag).to(have_sent_notification do |payload, _headers|
+      event = get_event_from_payload(payload)
+
+      expect(event["metaData"]["important"]).to eq({ "hello" => "world" })
+      expect(event["metaData"]["significant"]).to eq({ "hey" => "earth" })
+    end)
+  end
+
   it "can add callbacks in a configure block" do
     callback1 = proc {|report| report.add_tab(:important, { hello: "world" }) }
     callback2 = proc {|report| report.add_tab(:significant, { hey: "earth" }) }
 
     Bugsnag.configure do |config|
       config.add_on_error(callback1)
       config.add_on_error(callback2)
+      config.on_error do |report|
+        report.add_tab(:critical, { hi: "planet" })
+      end
     end
 
     Bugsnag.notify(RuntimeError.new("Oh no!"))
@@ -34,6 +51,7 @@
 
       expect(event["metaData"]["important"]).to eq({ "hello" => "world" })
       expect(event["metaData"]["significant"]).to eq({ "hey" => "earth" })
+      expect(event["metaData"]["critical"]).to eq({ "hi" => "planet" })
     end)
   end
 
@@ -56,6 +74,27 @@
     end)
   end
 
+  it "can remove an already registered block" do
+    callback1 = proc {|report| report.add_tab(:important, { hello: "world" }) }
+    callback2 = proc {|report| report.add_tab(:significant, { hey: "earth" }) }
+
+    Bugsnag.add_on_error(callback1)
+
+    # pass callback2 as a block so that it can be removed
+    Bugsnag.on_error(&callback2)
+
+    Bugsnag.remove_on_error(callback2)
+
+    Bugsnag.notify(RuntimeError.new("Oh no!"))
+
+    expect(Bugsnag).to(have_sent_notification do |payload, _headers|
+      event = get_event_from_payload(payload)
+
+      expect(event["metaData"]["important"]).to eq({ "hello" => "world" })
+      expect(event["metaData"]["significant"]).to be_nil
+    end)
+  end
+
   it "can remove all registered callbacks" do
     callback1 = proc {|report| report.add_tab(:important, { hello: "world" }) }
     callback2 = proc {|report| report.add_tab(:significant, { hey: "earth" }) }