fix inheritance edge case with formatless templates

Author: joelhawksley

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Fix bug where inheritance of components with formatless templates improperly raised a NoMethodError.
+
+    *GitHub Copilot*, *Joel Hawksley*, *Cameron Dutro*
+
 ## 4.6.0
 
 * Add `view_identifier` to the `render.view_component` instrumentation event payload, containing the path to the component's template file (e.g. `app/components/my_component.html.erb`). For components using inline render methods, `view_identifier` will be `nil`.

lib/view_component/template.rb

@@ -21,6 +21,13 @@ def initialize(component:, details:, lineno: nil, path: nil)
 
     class File < Template
       def initialize(component:, details:, path:)
+        # If the template file has no format (e.g. .erb instead of .html.erb),
+        # assume the default format (html).
+        if details.format.nil?
+          Kernel.warn("Template format for #{path} is missing, defaulting to :html.")
+          details = ActionView::TemplateDetails.new(details.locale, details.handler, DEFAULT_FORMAT, details.variant)
+        end
+
         @strip_annotation_line = false
 
         # Rails 8.1 added a newline to compiled ERB output (rails/rails#53731).

test/sandbox/app/components/format_less_child_component.erb

@@ -0,0 +1 @@
+<div class="child"><%= content %></div>

test/sandbox/app/components/format_less_child_component.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class FormatLessChildComponent < FormatLessParentComponent
+end

test/sandbox/app/components/format_less_parent_component.erb

@@ -0,0 +1 @@
+<div class="parent"><%= content %></div>

test/sandbox/app/components/format_less_parent_component.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class FormatLessParentComponent < ViewComponent::Base
+end

test/sandbox/test/rendering_test.rb

@@ -852,6 +852,18 @@ def test_inherited_component_overrides_inherits_template
     assert_selector("div", text: "hello, my own template")
   end
 
+  def test_inherited_component_with_format_less_template
+    # Reproduces https://github.com/ViewComponent/view_component/issues/2573
+    # When a parent component uses a format-less template (e.g. .erb or .slim
+    # instead of .html.erb or .html.slim), the child component crashes with
+    # "undefined method 'upcase' for nil" during compilation.
+    render_inline(FormatLessChildComponent.new) do
+      "Hello World"
+    end
+
+    assert_selector("div.child", text: "Hello World")
+  end
+
   def test_inherited_inline_component_inherits_inline_method
     render_inline(InlineInheritedComponent.new)