Register an offence for date strings without a timezone (rubocop#3951)

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#3915](https://github.com/bbatsov/rubocop/issues/3915): Make configurable whitelist for `Lint/SafeNavigationChain` cop. ([@pocke][])
 * [#3944](https://github.com/bbatsov/rubocop/issues/3944): Allow keyword arguments in `Style/RaiseArgs` cop. ([@mikegee][])
+* [#3951](https://github.com/bbatsov/rubocop/pull/3951): Make `Rails/Date` cop to register an offence for a string without timezone. ([@sinsoku][])
 
 ### New features
 
@@ -2617,3 +2618,4 @@
 [@zverok]: https://github.com/zverok
 [@backus]: https://github.com/backus
 [@pat]: https://github.com/pat
+[@sinsoku]: https://github.com/sinsoku

lib/rubocop/cop/rails/date.rb

@@ -54,13 +54,13 @@ def on_const(node)
  end
 
  def on_send(node)
- receiver, method_name, *args = *node
+ receiver, method_name = *node
  return unless receiver && bad_methods.include?(method_name)
 
  chain = extract_method_chain(node)
  return if safe_chain?(chain)
 
- return if method_name == :to_time && args.length == 1
+ return if method_name == :to_time && safe_to_time?(node)
 
  add_offense(node, :selector,
  format(MSG_SEND,
@@ -109,6 +109,16 @@ def safe_chain?(chain)
  (chain & bad_methods).empty? || !(chain & good_methods).empty?
  end
 
+ def safe_to_time?(node)
+ receiver, _method_name, *args = *node
+ if receiver.str_type?
+ zone_regexp = /[+-][\d:]+\z/
+ receiver.str_content.match(zone_regexp)
+ else
+ args.length == 1
+ end
+ end
+
  def good_days
  style == :strict ? [] : [:current, :yesterday, :tomorrow]
  end

spec/rubocop/cop/rails/date_spec.rb

@@ -49,6 +49,20 @@
  end
  end
 
+ context 'when a string literal with timezone' do
+ it 'does not register an offense' do
+ inspect_source(cop, '"2016-07-12 14:36:31 +0100".to_time(:utc)')
+ expect(cop.offenses).to be_empty
+ end
+ end
+
+ context 'when a string literal without timezone' do
+ it 'registers an offense' do
+ inspect_source(cop, '"2016-07-12 14:36:31".to_time(:utc)')
+ expect(cop.offenses.size).to eq(1)
+ end
+ end
+
  it 'does not blow up in the presence of a single constant to inspect' do
  inspect_source(cop, 'A')
  expect(cop.offenses).to be_empty