Deprecate rendering templates with . in the name

Allowing templates with "." introduces some ambiguity. Is index.html.erb
a template named "index" with format "html", or is it a template named
"index.html" without a format? We know it's probably the former, but if
we asked ActionView to render "index.html" we would currently get some
combination of the two: a Template with index.html as the name and
virtual path, but with html as the format.

This deprecates having "." anywhere in the template's name, we should
reserve this character for specifying formats. I think in 99% of cases
this will be people specifying `index.html` instead of simply `index`.

This was actually once deprecated in the 3.x series (removed in
6c57177f2c) but I don't think we can rely
on nobody having introduced this in the past 8 years.

actionpack/test/controller/render_test.rb

@@ -365,7 +365,9 @@ class ExpiresInRenderTest < ActionController::TestCase
   def test_dynamic_render
     assert File.exist?(File.expand_path("../../test/abstract_unit.rb", __dir__))
     assert_raises ActionView::MissingTemplate do
-      get :dynamic_render, params: { id: '../\\../test/abstract_unit.rb' }
+      assert_deprecated do
+        get :dynamic_render, params: { id: '../\\../test/abstract_unit.rb' }
+      end
     end
   end
 

actionpack/test/controller/renderer_test.rb

@@ -109,7 +109,7 @@ class RendererTest < ActiveSupport::TestCase
     xml  = "<p>Hello world!</p>\n"
 
     assert_equal html, render["respond_to/using_defaults"]
-    assert_equal xml,  render["respond_to/using_defaults.xml.builder"]
+    assert_equal xml,  assert_deprecated { render["respond_to/using_defaults.xml.builder"] }
     assert_equal xml,  render["respond_to/using_defaults", formats: :xml]
   end
 

actionview/lib/action_view/template/resolver.rb

@@ -227,6 +227,10 @@ module ActionView
       end
 
       def find_template_paths_from_details(path, details)
+        if path.name.include?(".")
+          ActiveSupport::Deprecation.warn("Rendering actions with '.' in the name is deprecated: #{path}")
+        end
+
         query = build_query(path, details)
         find_template_paths(query)
       end
@@ -331,6 +335,11 @@ module ActionView
       end
 
       def find_template_paths_from_details(path, details)
+        if path.name.include?(".")
+          # Fall back to the unoptimized resolver, which will warn
+          return super
+        end
+
         candidates = find_candidate_template_paths(path)
 
         regex = build_regex(path, details)

actionview/test/template/fallback_file_system_resolver_test.rb

@@ -8,7 +8,7 @@ class FallbackFileSystemResolverTest < ActiveSupport::TestCase
   end
 
   def test_should_have_no_virtual_path
-    templates = @root_resolver.find_all("hello_world.erb", "#{FIXTURE_LOAD_PATH}/test", false, locale: [], formats: [:html], variants: [], handlers: [:erb])
+    templates = @root_resolver.find_all("hello_world", "#{FIXTURE_LOAD_PATH}/test", false, locale: [], formats: [:html], variants: [], handlers: [:erb])
     assert_equal 1, templates.size
     assert_equal "Hello world!", templates[0].source
     assert_nil templates[0].virtual_path

actionview/test/template/render_test.rb

@@ -200,7 +200,9 @@ module RenderTestCases
   def test_render_outside_path
     assert File.exist?(File.expand_path("../../test/abstract_unit.rb", __dir__))
     assert_raises ActionView::MissingTemplate do
-      @view.render(template: "../\\../test/abstract_unit.rb")
+      assert_deprecated do
+        @view.render(template: "../\\../test/abstract_unit.rb")
+      end
     end
   end
 
@@ -338,8 +340,10 @@ module RenderTestCases
   end
 
   def test_render_partial_collection_with_partial_name_containing_dot
-    assert_equal "Hello: davidHello: mary",
+    assert_deprecated do
-      @view.render(partial: "test/customer.mobile", collection: [ Customer.new("david"), Customer.new("mary") ])
+      assert_equal "Hello: davidHello: mary",
+        @view.render(partial: "test/customer.mobile", collection: [ Customer.new("david"), Customer.new("mary") ])
+    end
   end
 
   def test_render_partial_collection_as_by_string
@@ -579,7 +583,11 @@ module RenderTestCases
   def test_render_ignores_templates_with_malformed_template_handlers
     %w(malformed malformed.erb malformed.html.erb malformed.en.html.erb).each do |name|
       assert File.exist?(File.expand_path("#{FIXTURE_LOAD_PATH}/test/malformed/#{name}~")), "Malformed file (#{name}~) which should be ignored does not exists"
-      assert_raises(ActionView::MissingTemplate) { @view.render(template: "test/malformed/#{name}") }
+      assert_raises(ActionView::MissingTemplate) do
+        ActiveSupport::Deprecation.silence do
+          @view.render(template: "test/malformed/#{name}")
+        end
+      end
     end
   end
 

actionview/test/template/resolver_shared_tests.rb

@@ -169,7 +169,7 @@ module ResolverSharedTests
   def test_virtual_path_is_preserved_with_dot
     with_file "test/hello_world.html.erb", "Hello html!"
 
-    template = context.find("hello_world.html", "test", false, [], {})
+    template = assert_deprecated { context.find("hello_world.html", "test", false, [], {}) }
     assert_equal "test/hello_world.html", template.virtual_path
 
     template = context.find("hello_world", "test", false, [], {})