4 files changed, 128 insertions, 0 deletions
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 301b0c8822..4c7b134c35 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,35 @@
+*   Introduce `ActiveSupport::ActionableError`.
+
+    Actionable errors let's you dispatch actions from Rails' error pages. This
+    can help you save time if you have a clear action for the resolution of
+    common development errors.
+
+    The de-facto example are pending migrations. Every time pending migrations
+    are found, a middleware raises an error. With actionable errors, you can
+    run the migrations right from the error page. Other examples include Rails
+    plugins that need to run a rake task to setup themselves. They can now
+    raise actionable errors to run the setup straight from the error pages.
+
+    Here is how to define an actionable error:
+
+    ```ruby
+    class PendingMigrationError < MigrationError #:nodoc:
+      include ActiveSupport::ActionableError
+
+      action "Run pending migrations" do
+        ActiveRecord::Tasks::DatabaseTasks.migrate
+      end
+    end
+    ```
+
+    To make an error actionable, include the `ActiveSupport::ActionableError`
+    module and invoke the `action` class macro to define the action. An action
+    needs a name and a procedure to execute. The name is shown as the name of a
+    button on the error pages. Once clicked, it will invoke the given
+    procedure.
+
+    *Vipul A M*, *Yao Jie*, *Genadi Samokovarov*
+
 *   Preserve `html_safe?` status on `ActiveSupport::SafeBuffer#*`.
 
     Before:
diff --git a/activesupport/lib/active_support.rb b/activesupport/lib/active_support.rb
index 5589c71281..9e242ddeaa 100644
--- a/activesupport/lib/active_support.rb
+++ b/activesupport/lib/active_support.rb
@@ -34,6 +34,7 @@ module ActiveSupport
   extend ActiveSupport::Autoload
 
   autoload :Concern
+  autoload :ActionableError
   autoload :CurrentAttributes
   autoload :Dependencies
   autoload :DescendantsTracker
diff --git a/activesupport/lib/active_support/actionable_error.rb b/activesupport/lib/active_support/actionable_error.rb
new file mode 100644
index 0000000000..7db14cd178
--- /dev/null
+++ b/activesupport/lib/active_support/actionable_error.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+module ActiveSupport
+  # Actionable errors let's you define actions to resolve an error.
+  #
+  # To make an error actionable, include the <tt>ActiveSupport::ActionableError</tt>
+  # module and invoke the +action+ class macro to define the action. An action
+  # needs a name and a block to execute.
+  module ActionableError
+    extend Concern
+
+    class NonActionable < StandardError; end
+
+    included do
+      class_attribute :_actions, default: {}
+    end
+
+    def self.actions(error) # :nodoc:
+      case error
+      when ActionableError, -> it { Class === it && it < ActionableError }
+        error._actions
+      else
+        {}
+      end
+    end
+
+    def self.dispatch(error, name) # :nodoc:
+      actions(error).fetch(name).call
+    rescue KeyError
+      raise NonActionable, "Cannot find action \"#{name}\""
+    end
+
+    module ClassMethods
+      # Defines an action that can resolve the error.
+      #
+      #   class PendingMigrationError < MigrationError
+      #     include ActiveSupport::ActionableError
+      #
+      #     action "Run pending migrations" do
+      #       ActiveRecord::Tasks::DatabaseTasks.migrate
+      #     end
+      #   end
+      def action(name, &block)
+        _actions[name] = block
+      end
+    end
+  end
+end
diff --git a/activesupport/test/actionable_error_test.rb b/activesupport/test/actionable_error_test.rb
new file mode 100644
index 0000000000..63046b937c
--- /dev/null
+++ b/activesupport/test/actionable_error_test.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+require "active_support/actionable_error"
+
+class ActionableErrorTest < ActiveSupport::TestCase
+  NonActionableError = Class.new(StandardError)
+
+  class DispatchableError < StandardError
+    include ActiveSupport::ActionableError
+
+    class_attribute :flip1, default: false
+    class_attribute :flip2, default: false
+
+    action "Flip 1" do
+      self.flip1 = true
+    end
+
+    action "Flip 2" do
+      self.flip2 = true
+    end
+  end
+
+  test "returns all action of an actionable error" do
+    assert_equal ["Flip 1", "Flip 2"], ActiveSupport::ActionableError.actions(DispatchableError).keys
+    assert_equal ["Flip 1", "Flip 2"], ActiveSupport::ActionableError.actions(DispatchableError.new).keys
+  end
+
+  test "returns no actions for non-actionable errors" do
+    assert ActiveSupport::ActionableError.actions(Exception).empty?
+    assert ActiveSupport::ActionableError.actions(Exception.new).empty?
+  end
+
+  test "dispatches actions from error and name" do
+    assert_changes "DispatchableError.flip1", from: false, to: true do
+      ActiveSupport::ActionableError.dispatch DispatchableError, "Flip 1"
+    end
+  end
+
+  test "cannot dispatch missing actions" do
+    err = assert_raises ActiveSupport::ActionableError::NonActionable do
+      ActiveSupport::ActionableError.dispatch NonActionableError, "action"
+    end
+
+    assert_equal 'Cannot find action "action"', err.to_s
+  end
+end