Add a way to temporarily opt-out to #all now lazily making requests:

- ### Problem

  In 9372d5a we made a change that
  defer the http request submission until the collection is used.

  ```ruby
  # Before

  Product.all #=> HTTP request is made

  # After

  products = Product.all #=> No HTTP request is made
  products.each { ... } #=> HTTP request is made here
  ```

  This create issues for codepaths that used to expect the
  `Product.all` to make the http request and this feels like
  a breaking change that should go through a deprecation cycle
  (too late now but let's have a way to opt-out to the new behaviour).

  ### Context

  We have a safety net in our application that does something like
  this:

  ```ruby
    products = allow_explicit_http_connections do
      Product.all
    end

    products.each { ... }
  ```

  This is now broken because we make the request outside of the
  explictly allowed resiliency block.

  ### Solution

  Introduce a way to opt out to the new behaviour and trigger a
  deprecation warning.

Author: Edouard-chin

README.md

@@ -192,6 +192,16 @@ people = Person.where(last_name: "Durden")
 people.first  # => <Person::xxx 'first_name' => 'Tyler' ...>
 ```
 
+##### A note on finding all resources
+
+Previously, Active Resource would eagerly load resources when `Person.all` was called. This behaviour is now
+deprecated and Active Resource now lazy loads collections. The http request is deferred until the collection is
+explicitly accessed.
+
+You can opt-in to the new behaviour by setting the `ActiveResource::Base.lazy_collections = false`.
+Note that this setting is temporary to allow your application to progressivly transition to the new behaviour.
+This setting will be removed in the next versions of Active Resource.
+
 ### Create
 
 Creating a new resource submits the JSON form of the resource as the body of the request and expects

lib/active_resource/base.rb

@@ -371,6 +371,7 @@ def self.logger=(logger)
       @@logger = logger
     end
 
+    class_attribute :lazy_collections, default: true, instance_accessor: false
     class_attribute :_query_format
     class_attribute :_format
     class_attribute :_collection_parser
@@ -384,6 +385,16 @@ class << self
       include ThreadsafeAttributes
       threadsafe_attribute :_headers, :_connection, :_user, :_password, :_bearer_token, :_site, :_proxy
 
+      def new_lazy_collections=(value)
+        ActiveResource.deprecator.warn(<<~MSG)
+          ActiveResource::Base#lazy_collections= is deprecated with no replacement.
+        MSG
+
+        self.old_lazy_collections = value
+      end
+      alias_method :old_lazy_collections=, :lazy_collections=
+      alias_method :lazy_collections=, :new_lazy_collections=
+
       # Creates a schema for this resource - setting the attributes that are
       # known prior to fetching an instance from the remote system.
       #
@@ -1126,7 +1137,11 @@ def last(*args)
       # This is an alias for find(:all). You can pass in all the same
       # arguments to this method as you can to <tt>find(:all)</tt>
       def all(*args)
-        WhereClause.new(self, *args)
+        if lazy_collections
+          WhereClause.new(self, *args)
+        else
+          find(:all, *args)
+        end
       end
 
       # This is an alias for all. You can pass in all the same

test/cases/finder_test.rb

@@ -61,6 +61,30 @@ def test_all
     assert_equal "David", all.last.name
   end
 
+  def test_all_loads_the_collection_lazily
+    all = Person.all
+    assert_empty(ActiveResource::HttpMock.requests)
+
+    assert_equal(2, all.size)
+    assert_not_empty(ActiveResource::HttpMock.requests)
+  end
+
+  def test_all_loads_the_collection_eagerly
+    previous_value = ActiveResource::Base.lazy_collections
+
+    assert_deprecated(/ActiveResource::Base#lazy_collections= is deprecated/, ActiveResource.deprecator) do
+      ActiveResource::Base.lazy_collections = false
+    end
+
+    all = Person.all
+    assert_not_empty(ActiveResource::HttpMock.requests)
+    assert_equal(2, all.size)
+  ensure
+    assert_deprecated(/ActiveResource::Base#lazy_collections= is deprecated/, ActiveResource.deprecator) do
+      ActiveResource::Base.lazy_collections = previous_value
+    end
+  end
+
   def test_all_with_params
     all = StreetAddress.all(params: { person_id: 1 })
     assert_equal 1, all.size