Introduce Template::File as new render file:

The previous behaviour of render file: was essentially the same as
render template:, except that templates can be specified as an absolute
path on the filesystem.

This makes sense for historic reasons, but now render file: is almost
exclusively used to render raw files (not .erb) like public/404.html. In
addition to complicating the code in template/resolver.rb, I think the
current behaviour is surprising to developers.

This commit deprecates the existing "lookup a template from anywhere"
behaviour and replaces it with "render this file exactly as it is on
disk". Handlers will no longer be used (it will render the same as if
the :raw handler was used), but formats (.html, .xml, etc) will still be
detected (and will default to :plain).

The existing render file: behaviour was the path through which Rails
apps were vulnerable in the recent CVE-2019-5418. Although the
vulnerability has been patched in a fully backwards-compatible way, I
think it's a strong hint that we should drop the existing
previously-vulnerable behaviour if it isn't a benefit to developers.

10 files changed, 110 insertions, 31 deletions

diff --git a/actionview/lib/action_view/file_template.rb b/actionview/lib/action_view/file_template.rb
index dea02176eb..e0dc7da3b6 100644
--- a/actionview/lib/action_view/file_template.rb
+++ b/actionview/lib/action_view/file_template.rb
@@ -11,7 +11,7 @@ module ActionView
     end
 
     def source
-      File.binread @filename
+      ::File.binread @filename
     end
 
     def refresh(_)
diff --git a/actionview/lib/action_view/renderer/template_renderer.rb b/actionview/lib/action_view/renderer/template_renderer.rb
index 9548fe12c4..60cb2ceafa 100644
--- a/actionview/lib/action_view/renderer/template_renderer.rb
+++ b/actionview/lib/action_view/renderer/template_renderer.rb
@@ -26,7 +26,12 @@ module ActionView
         elsif options.key?(:html)
           Template::HTML.new(options[:html], formats.first)
         elsif options.key?(:file)
-          @lookup_context.with_fallbacks.find_file(options[:file], nil, false, keys, @details)
+          if File.exist?(options[:file])
+            Template::File.new(options[:file])
+          else
+            ActiveSupport::Deprecation.warn "render file: should be given the absolute path to a file"
+            @lookup_context.with_fallbacks.find_file(options[:file], nil, false, keys, @details)
+          end
         elsif options.key?(:inline)
           handler = Template.handler_for_extension(options[:type] || "erb")
           format = if handler.respond_to?(:default_format)
diff --git a/actionview/lib/action_view/template.rb b/actionview/lib/action_view/template.rb
index 6e3af1536a..2230de2ca2 100644
--- a/actionview/lib/action_view/template.rb
+++ b/actionview/lib/action_view/template.rb
@@ -113,6 +113,7 @@ module ActionView
 
     eager_autoload do
       autoload :Error
+      autoload :File
       autoload :Handlers
       autoload :HTML
       autoload :Inline
@@ -139,7 +140,7 @@ module ActionView
       @virtual_path      = virtual_path
 
       @variable = if @virtual_path
-        base = @virtual_path[-1] == "/" ? "" : File.basename(@virtual_path)
+        base = @virtual_path[-1] == "/" ? "" : ::File.basename(@virtual_path)
         base =~ /\A_?(.*?)(?:\.\w+)*\z/
         $1.to_sym
       end
diff --git a/actionview/lib/action_view/template/error.rb b/actionview/lib/action_view/template/error.rb
index 4e3c02e05e..e6d9e35815 100644
--- a/actionview/lib/action_view/template/error.rb
+++ b/actionview/lib/action_view/template/error.rb
@@ -104,7 +104,7 @@ module ActionView
       def line_number
         @line_number ||=
           if file_name
-            regexp = /#{Regexp.escape File.basename(file_name)}:(\d+)/
+            regexp = /#{Regexp.escape ::File.basename(file_name)}:(\d+)/
             $1 if message =~ regexp || backtrace.find { |line| line =~ regexp }
           end
       end
diff --git a/actionview/lib/action_view/template/file.rb b/actionview/lib/action_view/template/file.rb
new file mode 100644
index 0000000000..487e5735cf
--- /dev/null
+++ b/actionview/lib/action_view/template/file.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module ActionView #:nodoc:
+  # = Action View File Template
+  class Template #:nodoc:
+    class File #:nodoc:
+      attr_accessor :type, :format
+
+      def initialize(filename)
+        @filename = filename.to_s
+        extname = ::File.extname(filename).delete(".")
+        @type = Template::Types[extname] || Template::Types[:text]
+        @format = @type.symbol
+      end
+
+      def identifier
+        @filename
+      end
+
+      def render(*args)
+        ::File.read(@filename)
+      end
+
+      def formats; Array(format); end
+      deprecate :formats
+    end
+  end
+end
diff --git a/actionview/test/actionpack/abstract/render_test.rb b/actionview/test/actionpack/abstract/render_test.rb
index d863548a5c..e4e8ac93b2 100644
--- a/actionview/test/actionpack/abstract/render_test.rb
+++ b/actionview/test/actionpack/abstract/render_test.rb
@@ -26,7 +26,7 @@ module AbstractController
       end
 
       def file
-        render file: "some/file"
+        ActiveSupport::Deprecation.silence { render file: "some/file" }
       end
 
       def inline
diff --git a/actionview/test/actionpack/controller/render_test.rb b/actionview/test/actionpack/controller/render_test.rb
index 52c3c54d96..c8ce7366d1 100644
--- a/actionview/test/actionpack/controller/render_test.rb
+++ b/actionview/test/actionpack/controller/render_test.rb
@@ -872,48 +872,64 @@ class RenderTest < ActionController::TestCase
 
   # :ported:
   def test_render_file_with_instance_variables
-    get :render_file_with_instance_variables
+    assert_deprecated do
+      get :render_file_with_instance_variables
+    end
     assert_equal "The secret is in the sauce\n", @response.body
   end
 
   def test_render_file
-    get :hello_world_file
+    assert_deprecated do
+      get :hello_world_file
+    end
     assert_equal "Hello world!", @response.body
   end
 
   # :ported:
   def test_render_file_not_using_full_path
-    get :render_file_not_using_full_path
+    assert_deprecated do
+      get :render_file_not_using_full_path
+    end
     assert_equal "The secret is in the sauce\n", @response.body
   end
 
   # :ported:
   def test_render_file_not_using_full_path_with_dot_in_path
-    get :render_file_not_using_full_path_with_dot_in_path
+    assert_deprecated do
+      get :render_file_not_using_full_path_with_dot_in_path
+    end
     assert_equal "The secret is in the sauce\n", @response.body
   end
 
   # :ported:
   def test_render_file_using_pathname
-    get :render_file_using_pathname
+    assert_deprecated do
+      get :render_file_using_pathname
+    end
     assert_equal "The secret is in the sauce\n", @response.body
   end
 
   # :ported:
   def test_render_file_with_locals
-    get :render_file_with_locals
+    assert_deprecated do
+      get :render_file_with_locals
+    end
     assert_equal "The secret is in the sauce\n", @response.body
   end
 
   # :ported:
   def test_render_file_as_string_with_locals
-    get :render_file_as_string_with_locals
+    assert_deprecated do
+      get :render_file_as_string_with_locals
+    end
     assert_equal "The secret is in the sauce\n", @response.body
   end
 
   # :assessed:
   def test_render_file_from_template
-    get :render_file_from_template
+    assert_deprecated do
+      get :render_file_from_template
+    end
     assert_equal "The secret is in the sauce\n", @response.body
   end
 
@@ -1133,11 +1149,19 @@ class RenderTest < ActionController::TestCase
   end
 
   def test_bad_render_to_string_still_throws_exception
-    assert_raise(ActionView::MissingTemplate) { get :render_to_string_with_exception }
+    assert_deprecated do
+      assert_raise(ActionView::MissingTemplate) do
+        get :render_to_string_with_exception
+      end
+    end
   end
 
   def test_render_to_string_that_throws_caught_exception_doesnt_break_assigns
-    assert_nothing_raised { get :render_to_string_with_caught_exception }
+    assert_deprecated do
+      assert_nothing_raised do
+        get :render_to_string_with_caught_exception
+      end
+    end
     assert_equal "i'm before the render", @controller.instance_variable_get(:@before)
     assert_equal "i'm after the render", @controller.instance_variable_get(:@after)
   end
diff --git a/actionview/test/template/log_subscriber_test.rb b/actionview/test/template/log_subscriber_test.rb
index 85735139c1..8b160a7336 100644
--- a/actionview/test/template/log_subscriber_test.rb
+++ b/actionview/test/template/log_subscriber_test.rb
@@ -51,9 +51,20 @@ class AVLogSubscriberTest < ActiveSupport::TestCase
     def @view.combined_fragment_cache_key(*); "ahoy `controller` dependency"; end
   end
 
+  def test_render_template_template
+    Rails.stub(:root, File.expand_path(FIXTURE_LOAD_PATH)) do
+      @view.render(template: "test/hello_world")
+      wait
+
+      assert_equal 2, @logger.logged(:info).size
+      assert_match(/Rendering test\/hello_world\.erb/, @logger.logged(:info).first)
+      assert_match(/Rendered test\/hello_world\.erb/, @logger.logged(:info).last)
+    end
+  end
+
   def test_render_file_template
     Rails.stub(:root, File.expand_path(FIXTURE_LOAD_PATH)) do
-      @view.render(file: "test/hello_world")
+      @view.render(file: "#{FIXTURE_LOAD_PATH}/test/hello_world.erb")
       wait
 
       assert_equal 2, @logger.logged(:info).size
diff --git a/actionview/test/template/render_test.rb b/actionview/test/template/render_test.rb
index f0fed601f8..3cf3903a58 100644
--- a/actionview/test/template/render_test.rb
+++ b/actionview/test/template/render_test.rb
@@ -53,15 +53,20 @@ module RenderTestCases
     assert_match(/You invoked render but did not give any of (.+) option\./, e.message)
   end
 
+  def test_render_template
+    assert_equal "Hello world!", @view.render(template: "test/hello_world")
+  end
+
+
   def test_render_file
-    assert_equal "Hello world!", @view.render(file: "test/hello_world")
+    assert_equal "Hello world!", assert_deprecated { @view.render(file: "test/hello_world") }
   end
 
   # Test if :formats, :locale etc. options are passed correctly to the resolvers.
   def test_render_file_with_format
-    assert_match "<h1>No Comment</h1>", @view.render(file: "comments/empty", formats: [:html])
-    assert_match "<error>No Comment</error>", @view.render(file: "comments/empty", formats: [:xml])
-    assert_match "<error>No Comment</error>", @view.render(file: "comments/empty", formats: :xml)
+    assert_match "<h1>No Comment</h1>", assert_deprecated { @view.render(file: "comments/empty", formats: [:html]) }
+    assert_match "<error>No Comment</error>", assert_deprecated { @view.render(file: "comments/empty", formats: [:xml]) }
+    assert_match "<error>No Comment</error>", assert_deprecated { @view.render(file: "comments/empty", formats: :xml) }
   end
 
   def test_render_template_with_format
@@ -94,8 +99,8 @@ module RenderTestCases
   end
 
   def test_render_file_with_locale
-    assert_equal "<h1>Kein Kommentar</h1>", @view.render(file: "comments/empty", locale: [:de])
-    assert_equal "<h1>Kein Kommentar</h1>", @view.render(file: "comments/empty", locale: :de)
+    assert_equal "<h1>Kein Kommentar</h1>", assert_deprecated { @view.render(file: "comments/empty", locale: [:de]) }
+    assert_equal "<h1>Kein Kommentar</h1>", assert_deprecated { @view.render(file: "comments/empty", locale: :de) }
   end
 
   def test_render_template_with_locale
@@ -107,8 +112,8 @@ module RenderTestCases
   end
 
   def test_render_file_with_handlers
-    assert_equal "<h1>No Comment</h1>\n", @view.render(file: "comments/empty", handlers: [:builder])
-    assert_equal "<h1>No Comment</h1>\n", @view.render(file: "comments/empty", handlers: :builder)
+    assert_equal "<h1>No Comment</h1>\n", assert_deprecated { @view.render(file: "comments/empty", handlers: [:builder]) }
+    assert_equal "<h1>No Comment</h1>\n", assert_deprecated { @view.render(file: "comments/empty", handlers: :builder) }
   end
 
   def test_render_template_with_handlers
@@ -156,22 +161,27 @@ module RenderTestCases
     assert_equal "Elastica", @view.render(template: "/shared")
   end
 
-  def test_render_file_with_full_path
+  def test_render_file_with_full_path_no_extension
     template_path = File.expand_path("../fixtures/test/hello_world", __dir__)
+    assert_equal "Hello world!", assert_deprecated { @view.render(file: template_path) }
+  end
+
+  def test_render_file_with_full_path
+    template_path = File.expand_path("../fixtures/test/hello_world.erb", __dir__)
     assert_equal "Hello world!", @view.render(file: template_path)
   end
 
   def test_render_file_with_instance_variables
-    assert_equal "The secret is in the sauce\n", @view.render(file: "test/render_file_with_ivar")
+    assert_equal "The secret is in the sauce\n", assert_deprecated { @view.render(file: "test/render_file_with_ivar") }
   end
 
   def test_render_file_with_locals
     locals = { secret: "in the sauce" }
-    assert_equal "The secret is in the sauce\n", @view.render(file: "test/render_file_with_locals", locals: locals)
+    assert_equal "The secret is in the sauce\n", assert_deprecated { @view.render(file: "test/render_file_with_locals", locals: locals) }
   end
 
   def test_render_file_not_using_full_path_with_dot_in_path
-    assert_equal "The secret is in the sauce\n", @view.render(file: "test/dot.directory/render_file_with_ivar")
+    assert_equal "The secret is in the sauce\n", assert_deprecated { @view.render(file: "test/dot.directory/render_file_with_ivar") }
   end
 
   def test_render_partial_from_default
@@ -286,7 +296,7 @@ module RenderTestCases
   end
 
   def test_render_file_with_errors
-    e = assert_raises(ActionView::Template::Error) { @view.render(file: File.expand_path("test/_raise", FIXTURE_LOAD_PATH)) }
+    e = assert_raises(ActionView::Template::Error) { assert_deprecated { @view.render(file: File.expand_path("test/_raise", FIXTURE_LOAD_PATH)) } }
     assert_match %r!method.*doesnt_exist!, e.message
     assert_equal "", e.sub_template_message
     assert_equal "1", e.line_number
diff --git a/actionview/test/template/streaming_render_test.rb b/actionview/test/template/streaming_render_test.rb
index a5b59a700e..a5e673e71e 100644
--- a/actionview/test/template/streaming_render_test.rb
+++ b/actionview/test/template/streaming_render_test.rb
@@ -47,12 +47,12 @@ class FiberedTest < SetupFiberedBase
   end
 
   def test_render_file
-    assert_equal "Hello world!", buffered_render(file: "test/hello_world")
+    assert_equal "Hello world!", assert_deprecated { buffered_render(file: "test/hello_world") }
   end
 
   def test_render_file_with_locals
     locals = { secret: "in the sauce" }
-    assert_equal "The secret is in the sauce\n", buffered_render(file: "test/render_file_with_locals", locals: locals)
+    assert_equal "The secret is in the sauce\n", assert_deprecated { buffered_render(file: "test/render_file_with_locals", locals: locals) }
   end
 
   def test_render_partial