[Fix rubocop#227] Make Rails/UniqueValidationWithoutIndex aware of …

…updating schema.rb

Fixes rubocop#227.

This PR makes `Rails/UniqueValidationWithoutIndex` aware of updating
db/schema.rb

`Rails/UniqueValidationWithoutIndex` cop needs to know both model
and db/schema.rb changes to register an offense. However, with
default RuboCop, only changes to the model affect cache behavior.

This PR ensures that changes to db/schema.rb affect the cache by
overriding the following method:

```ruby
# This method should be overridden when a cop's behavior depends
# on state that lives outside of these locations:
#
#   (1) the file under inspection
#   (2) the cop's source code
#   (3) the config (eg a .rubocop.yml file)
#
# For example, some cops may want to look at other parts of
# the codebase being inspected to find violations. A cop may
# use the presence or absence of file `foo.rb` to determine
# whether a certain violation exists in `bar.rb`.
#
# Overriding this method allows the cop to indicate to RuboCop's
# ResultCache system when those external dependencies change,
# ie when the ResultCache should be invalidated.
def external_dependency_checksum
  nil
end
```

https://github.com/rubocop-hq/rubocop/blob/v0.81.0/lib/rubocop/cop/cop.rb#L222-L239

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Bug fixes
+
+* [#227](https://github.com/rubocop-hq/rubocop-rails/issues/227): Make `Rails/UniqueValidationWithoutIndex` aware of updating db/schema.rb. ([@koic][])
+
 ## 2.5.1 (2020-04-02)
 
 ### Bug fixes

lib/rubocop/cop/mixin/active_record_helper.rb

@@ -14,6 +14,20 @@ module ActiveRecordHelper
         (send nil? :belongs_to {str sym} ...)
       PATTERN
 
+      def external_dependency_checksum
+        if defined?(@external_dependency_checksum)
+          return @external_dependency_checksum
+        end
+
+        schema_code = File.read(RuboCop::Rails::SchemaLoader.db_schema_path)
+
+        @external_dependency_checksum ||= Digest::SHA1.hexdigest(schema_code)
+      end
+
+      def schema
+        RuboCop::Rails::SchemaLoader.load(target_ruby_version)
+      end
+
       def table_name(class_node)
         table_name = find_set_table_name(class_node).to_a.last&.first_argument
         return table_name.value.to_s if table_name

lib/rubocop/cop/rails/unique_validation_without_index.rb

@@ -149,10 +149,6 @@ def array_node_to_array(node)
             end
           end
         end
-
-        def schema
-          RuboCop::Rails::SchemaLoader.load(target_ruby_version)
-        end
       end
     end
   end

lib/rubocop/rails/schema_loader.rb

@@ -24,16 +24,6 @@ def reset!
         remove_instance_variable(:@schema)
       end
 
-      private
-
-      def load!(target_ruby_version)
-        path = db_schema_path
-        return unless path
-
-        ast = parse(path, target_ruby_version)
-        Schema.new(ast)
-      end
-
       def db_schema_path
         path = Pathname.pwd
         until path.root?
@@ -46,6 +36,16 @@ def db_schema_path
         nil
       end
 
+      private
+
+      def load!(target_ruby_version)
+        path = db_schema_path
+        return unless path
+
+        ast = parse(path, target_ruby_version)
+        Schema.new(ast)
+      end
+
       def parse(path, target_ruby_version)
         klass_name = :"Ruby#{target_ruby_version.to_s.sub('.', '')}"
         klass = ::Parser.const_get(klass_name)