allow action menu to auto overflow its contents

app/components/primer/alpha/action_menu.rb

@@ -154,6 +154,7 @@ class ActionMenu < Primer::Component
       # @param dynamic_label_prefix [String] If provided, the prefix is prepended to the dynamic label and displayed in the show button.
       # @param select_variant [Symbol] <%= one_of(Primer::Alpha::ActionMenu::SELECT_VARIANT_OPTIONS) %>
       # @param form_arguments [Hash] Allows an `ActionMenu` to act as a select list in multi- and single-select modes. Pass the `builder:` and `name:` options to this hash. `builder:` should be an instance of `ActionView::Helpers::FormBuilder`, which are created by the standard Rails `#form_with` and `#form_for` helpers. The `name:` option is the desired name of the field that will be included in the params sent to the server on form submission.
+      # @param overflow [Symbol] Control the overflow behavior of the menu. <%= one_of(Primer::Alpha::Overlay::OVERFLOW_OPTIONS) %>. Defaults to `<%= Primer::Alpha::Overlay::DEFAULT_OVERFLOW_STYLE %>`.
       # @param system_arguments [Hash] <%= link_to_system_arguments_docs %>.
       def initialize(
         menu_id: self.class.generate_id,
@@ -166,6 +167,7 @@ def initialize(
         dynamic_label_prefix: nil,
         select_variant: DEFAULT_SELECT_VARIANT,
         form_arguments: {},
+        overflow: Primer::Alpha::Overlay::DEFAULT_OVERFLOW_STYLE,
         **system_arguments
       )
         @menu_id = menu_id
@@ -188,7 +190,8 @@ def initialize(
           visually_hide_title: true,
           anchor_align: anchor_align,
           anchor_side: anchor_side,
-          size: size
+          size: size,
+          overflow: overflow,
         )
 
         @list = Primer::Alpha::ActionMenu::List.new(

app/components/primer/alpha/overlay.rb

@@ -65,6 +65,15 @@ class Overlay < Primer::Component
 
       ROLE_OPTIONS = [:dialog, :menu, nil].freeze
 
+      DEFAULT_OVERFLOW_STYLE = :auto
+      OVERFLOW_MAPPINGS = {
+        DEFAULT_OVERFLOW_STYLE => "overflow-y-auto",
+        :scroll => "overflow-y-scroll",
+        :hidden => "overflow-y-hidden",
+        :visible => "overflow-y-visible"
+      }.freeze
+      OVERFLOW_OPTIONS = OVERFLOW_MAPPINGS.keys
+
       # Optional button to open the Overlay.
       #
       # @param icon [String] Name of <%= link_to_octicons %> to use instead of text. If provided, a <%= link_to_component(Primer::Beta::IconButton) %> will be rendered. Otherwise a <%= link_to_component(Primer::Beta::Button) %> will be rendered.
@@ -135,6 +144,7 @@ class Overlay < Primer::Component
       # @param allow_out_of_bounds [Boolean] Allow the Overlay to overflow its container.
       # @param visually_hide_title [Boolean] If true will hide the heading title, while still making it available to Screen Readers.
       # @param role [String] The ARIA role. <%= one_of(Primer::Alpha::Overlay::ROLE_OPTIONS) %>
+      # @param overflow [Symbol] Sets the overflow behavior of the Overlay wrapper. <%= one_of(Primer::Alpha::Overlay::OVERFLOW_OPTIONS) %>.
       # @param system_arguments [Hash] <%= link_to_system_arguments_docs %>
       def initialize(
         title:,
@@ -150,6 +160,7 @@ def initialize(
         allow_out_of_bounds: false,
         visually_hide_title: false,
         id: self.class.generate_id,
+        overflow: nil,
         **system_arguments
       )
         @system_arguments = deny_tag_argument(**system_arguments)
@@ -159,7 +170,8 @@ def initialize(
         @system_arguments[:id] = id.to_s
         @wrapper_classes = class_names(
           "Overlay",
-          SIZE_MAPPINGS[fetch_or_fallback(SIZE_OPTIONS, size, DEFAULT_SIZE)]
+          SIZE_MAPPINGS[fetch_or_fallback(SIZE_OPTIONS, size, DEFAULT_SIZE)],
+          OVERFLOW_MAPPINGS[fetch_or_fallback(OVERFLOW_OPTIONS, overflow, DEFAULT_OVERFLOW_STYLE)] => overflow.present?
         )
         @system_arguments[:tag] = "anchored-position"
         @system_arguments[:anchor] = anchor || "overlay-show-#{@system_arguments[:id]}"