Do note remove `Content-Type` when `render :body`

`render :body` should just not set the `Content-Type` header. By
removing the header, it breaks the compatibility with other parts.

After this commit, `render :body` will returns `text/html` content type,
sets by default from `ActionDispatch::Response`, and it will preserve
the overridden content type if you override it.

Fixes #14197, #14238

This partially reverts commit 3047376870d4a7adc7ff15c3cb4852e073c8f1da.

5 files changed, 16 insertions, 42 deletions

diff --git a/actionpack/lib/action_controller/metal/rack_delegation.rb b/actionpack/lib/action_controller/metal/rack_delegation.rb
index e1bee9e60c..bdf6e88699 100644
--- a/actionpack/lib/action_controller/metal/rack_delegation.rb
+++ b/actionpack/lib/action_controller/metal/rack_delegation.rb
@@ -5,8 +5,8 @@ module ActionController
   module RackDelegation
     extend ActiveSupport::Concern
 
-    delegate :headers, :status=, :location=, :content_type=, :no_content_type=,
-             :status, :location, :content_type, :no_content_type, :to => "@_response"
+    delegate :headers, :status=, :location=, :content_type=,
+             :status, :location, :content_type, :to => "@_response"
 
     def dispatch(action, request)
       set_response!(request)
diff --git a/actionpack/lib/action_controller/metal/rendering.rb b/actionpack/lib/action_controller/metal/rendering.rb
index 3c4ef596c7..93e7d6954c 100644
--- a/actionpack/lib/action_controller/metal/rendering.rb
+++ b/actionpack/lib/action_controller/metal/rendering.rb
@@ -45,9 +45,7 @@ module ActionController
     def _process_format(format, options = {})
       super
 
-      if options[:body]
-        self.headers.delete "Content-Type"
-      elsif options[:plain]
+      if options[:plain]
         self.content_type = Mime::TEXT
       else
         self.content_type ||= format.to_s
diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index f14ca1ea44..2c6bcf7b7b 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -63,8 +63,6 @@ module ActionDispatch # :nodoc:
     # content you're giving them, so we need to send that along.
     attr_accessor :charset
 
-    attr_accessor :no_content_type # :nodoc:
-
     CONTENT_TYPE = "Content-Type".freeze
     SET_COOKIE   = "Set-Cookie".freeze
     LOCATION     = "Location".freeze
@@ -305,17 +303,8 @@ module ActionDispatch # :nodoc:
       !@sending_file && @charset != false
     end
 
-    def remove_content_type!
-      headers.delete CONTENT_TYPE
-    end
-
     def rack_response(status, header)
-      if no_content_type
-        remove_content_type!
-      else
-        assign_default_content_type_and_charset!(header)
-      end
-
+      assign_default_content_type_and_charset!(header)
       handle_conditional_get!
 
       header[SET_COOKIE] = header[SET_COOKIE].join("\n") if header[SET_COOKIE].respond_to?(:join)
diff --git a/actionpack/test/controller/new_base/render_body_test.rb b/actionpack/test/controller/new_base/render_body_test.rb
index a7e4f87bd9..fad848349a 100644
--- a/actionpack/test/controller/new_base/render_body_test.rb
+++ b/actionpack/test/controller/new_base/render_body_test.rb
@@ -65,6 +65,11 @@ module RenderBody
       render body: "hello world", layout: "greetings"
     end
 
+    def with_custom_content_type
+      response.headers['Content-Type'] = 'application/json'
+      render body: '["troll","face"]'
+    end
+
     def with_ivar_in_layout
       @ivar = "hello world"
       render body: "hello world", layout: "ivar"
@@ -141,6 +146,13 @@ module RenderBody
       assert_status 200
     end
 
+    test "specified content type should not be removed" do
+      get "/render_body/with_layout/with_custom_content_type"
+
+      assert_equal %w{ troll face }, JSON.parse(response.body)
+      assert_equal 'application/json', response.headers['Content-Type']
+    end
+
     test "rendering body with layout: false" do
       get "/render_body/with_layout/with_layout_false"
 
@@ -154,22 +166,5 @@ module RenderBody
       assert_body "hello world"
       assert_status 200
     end
-
-    test "rendering from minimal controller returns response with no content type" do
-      get "/render_body/minimal/index"
-
-      assert_header_no_content_type
-    end
-
-    test "rendering from normal controller returns response with no content type" do
-      get "/render_body/simple/index"
-
-      assert_header_no_content_type
-    end
-
-    def assert_header_no_content_type
-      assert_not response.headers.has_key?("Content-Type"),
-        %(Expect response not to have Content-Type header, got "#{response.headers["Content-Type"]}")
-    end
   end
 end
diff --git a/actionpack/test/dispatch/response_test.rb b/actionpack/test/dispatch/response_test.rb
index 1360ede3f8..959a3bc5cd 100644
--- a/actionpack/test/dispatch/response_test.rb
+++ b/actionpack/test/dispatch/response_test.rb
@@ -235,14 +235,6 @@ class ResponseTest < ActiveSupport::TestCase
       assert_equal @response.body, body.each.to_a.join
     end
   end
-
-  test "does not add default content-type if Content-Type is none" do
-    resp = ActionDispatch::Response.new.tap { |response|
-      response.no_content_type = true
-    }
-
-    assert_not resp.headers.has_key?('Content-Type')
-  end
 end
 
 class ResponseIntegrationTest < ActionDispatch::IntegrationTest