Refactor ActiveRecord::TokenFor to not rely on relation delegation

Ref: rails#50396
Ref: rails#51776

`ActiveRecord::Relation` automatically delegates missing methods
to the model class wrapped in a `scoping { }` block.

This is to support scoping in user defined class methods. The problem
however is that it's very error prone for the framework, because we
can mistakenly call model methods from inside `Relation` and not
realized we're applying a global scope.

In the best case scenario it's just a waste of performance, but
it can also lead to bugs like rails#51775

I'm planning to restrict this automatic delegation to methods defined
in childs of `ActiveRecord::Base` only: rails#50396
but for this to work we must first refactor any Rails code that rely on it.

Author: byroot

activerecord/lib/active_record/relation.rb

@@ -66,7 +66,7 @@ def exec_explain(&block)
 
     include Enumerable
     include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches, Explain, Delegation
-    include SignedId::RelationMethods
+    include SignedId::RelationMethods, TokenFor::RelationMethods
 
     attr_reader :table, :klass, :loaded, :predicate_builder
     attr_accessor :skip_preloading_value

activerecord/lib/active_record/token_for.rb

@@ -35,6 +35,24 @@ def resolve_token(token)
       end
     end
 
+    module RelationMethods
+      # Finds a record using a given +token+ for a predefined +purpose+. Returns
+      # +nil+ if the token is invalid or the record was not found.
+      def find_by_token_for(purpose, token)
+        raise UnknownPrimaryKey.new(self) unless model.primary_key
+        model.token_definitions.fetch(purpose).resolve_token(token) { |id| find_by(model.primary_key => id) }
+      end
+
+      # Finds a record using a given +token+ for a predefined +purpose+. Raises
+      # ActiveSupport::MessageVerifier::InvalidSignature if the token is invalid
+      # (e.g. expired, bad format, etc). Raises ActiveRecord::RecordNotFound if
+      # the token is valid but the record was not found.
+      def find_by_token_for!(purpose, token)
+        model.token_definitions.fetch(purpose).resolve_token(token) { |id| find(id) } ||
+          (raise ActiveSupport::MessageVerifier::InvalidSignature)
+      end
+    end
+
     module ClassMethods
       # Defines the behavior of tokens generated for a specific +purpose+.
       # A token can be generated by calling TokenFor#generate_token_for on a
@@ -85,20 +103,12 @@ def generates_token_for(purpose, expires_in: nil, &block)
         self.token_definitions = token_definitions.merge(purpose => TokenDefinition.new(self, purpose, expires_in, block))
       end
 
-      # Finds a record using a given +token+ for a predefined +purpose+. Returns
-      # +nil+ if the token is invalid or the record was not found.
-      def find_by_token_for(purpose, token)
-        raise UnknownPrimaryKey.new(self) unless primary_key
-        token_definitions.fetch(purpose).resolve_token(token) { |id| find_by(primary_key => id) }
+      def find_by_token_for(purpose, token) # :nodoc:
+        all.find_by_token_for(purpose, token)
       end
 
-      # Finds a record using a given +token+ for a predefined +purpose+. Raises
-      # ActiveSupport::MessageVerifier::InvalidSignature if the token is invalid
-      # (e.g. expired, bad format, etc). Raises ActiveRecord::RecordNotFound if
-      # the token is valid but the record was not found.
-      def find_by_token_for!(purpose, token)
-        token_definitions.fetch(purpose).resolve_token(token) { |id| find(id) } ||
-          (raise ActiveSupport::MessageVerifier::InvalidSignature)
+      def find_by_token_for!(purpose, token) # :nodoc:
+        all.find_by_token_for!(purpose, token)
       end
     end