Add #content? (#1649)

* #content is part of the public API

* #content? indicates of content has been passed to component

* add changelog, fix test names

* check for content being passed, not the content itself

Author: joelhawksley

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 5
 
 ## main
 
+* Add `#content?` method that indicates if content has been passed to component.
+
+    *Joel Hawksley*
+
 * Added example of a custom preview controller.
 
     *Graham Rogers*

lib/view_component/base.rb

@@ -245,22 +245,40 @@ def request
       @request ||= controller.request if controller.respond_to?(:request)
     end
 
-    private
-
-    attr_reader :view_context
-
+    # The content passed to the component instance as a block.
+    #
+    # @return [String]
     def content
       @__vc_content_evaluated = true
       return @__vc_content if defined?(@__vc_content)
 
       @__vc_content =
-        if @view_context && @__vc_render_in_block
+        if __vc_render_in_block_provided?
           view_context.capture(self, &@__vc_render_in_block)
-        elsif defined?(@__vc_content_set_by_with_content)
+        elsif __vc_content_set_by_with_content_defined?
           @__vc_content_set_by_with_content
         end
     end
 
+    # Whether `content` has been passed to the component.
+    #
+    # @return [Boolean]
+    def content?
+      __vc_render_in_block_provided? || __vc_content_set_by_with_content_defined?
+    end
+
+    private
+
+    attr_reader :view_context
+
+    def __vc_render_in_block_provided?
+      @view_context && @__vc_render_in_block
+    end
+
+    def __vc_content_set_by_with_content_defined?
+      defined?(@__vc_content_set_by_with_content)
+    end
+
     def content_evaluated?
       @__vc_content_evaluated
     end

test/sandbox/app/components/content_predicate_component.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class ContentPredicateComponent < ViewComponent::Base
+  def call
+    if content?
+      content
+    else
+      "Default"
+    end
+  end
+end

test/sandbox/test/rendering_test.rb

@@ -1038,4 +1038,16 @@ def test_concurrency_deadlock
       end
     end
   end
+
+  def test_content_predicate_false
+    render_inline(ContentPredicateComponent.new)
+
+    assert_text("Default")
+  end
+
+  def test_content_predicate_true
+    render_inline(ContentPredicateComponent.new.with_content("foo"))
+
+    assert_text("foo")
+  end
 end