[Fix #1094] Make Rails/TimeZone aware of String#to_time

Fixes #1094.

This PR make `Rails/TimeZone` aware of `String#to_time`.

Author: koic

changelog/change_make_rails_time_zone_aware_of_string_to_time

@@ -0,0 +1 @@
+* [#1094](https://github.com/rubocop/rubocop-rails/issues/1094): Make `Rails/TimeZone` aware of `String#to_time`. ([@koic][])

lib/rubocop/cop/rails/time_zone.rb

@@ -21,6 +21,7 @@ module Rails
       #   # bad
       #   Time.now
       #   Time.parse('2015-03-02T19:05:37')
+      #   '2015-03-02T19:05:37'.to_time
       #
       #   # good
       #   Time.current
@@ -44,19 +45,17 @@ class TimeZone < Base
         extend AutoCorrector
 
         MSG = 'Do not use `%<current>s` without zone. Use `%<prefer>s` instead.'
-
         MSG_ACCEPTABLE = 'Do not use `%<current>s` without zone. Use one of %<prefer>s instead.'
-
         MSG_LOCALTIME = 'Do not use `Time.localtime` without offset or zone.'
+        MSG_STRING_TO_TIME = 'Do not use `String#to_time` without zone. Use `Time.zone.parse` instead.'
 
         GOOD_METHODS = %i[zone zone_default find_zone find_zone!].freeze
-
         DANGEROUS_METHODS = %i[now local new parse at].freeze
-
         ACCEPTED_METHODS = %i[in_time_zone utc getlocal xmlschema iso8601 jisx0301 rfc3339 httpdate to_i to_f].freeze
-
         TIMEZONE_SPECIFIER = /([A-Za-z]|[+-]\d{2}:?\d{2})\z/.freeze
 
+        RESTRICT_ON_SEND = %i[to_time].freeze
+
         def on_const(node)
           mod, klass = *node
           # we should only check core classes
@@ -66,6 +65,14 @@ def on_const(node)
           check_time_node(klass, node.parent) if klass == :Time
         end
 
+        def on_send(node)
+          return if !node.receiver&.str_type? || !node.method?(:to_time)
+
+          add_offense(node.loc.selector, message: MSG_STRING_TO_TIME) do |corrector|
+            autocorrect(corrector, node)
+          end
+        end
+
         private
 
         def autocorrect(corrector, node)

spec/rubocop/cop/rails/time_zone_spec.rb

@@ -124,6 +124,19 @@
       end
     end
 
+    it 'registers an offense for `String#to_time`' do
+      expect_offense(<<~RUBY)
+        "2012-03-02 16:05:37".to_time
+                              ^^^^^^^ Do not use `String#to_time` without zone. Use `Time.zone.parse` instead.
+      RUBY
+    end
+
+    it 'does not register an offense for `to_time` without receiver' do
+      expect_no_offenses(<<~RUBY)
+        to_time
+      RUBY
+    end
+
     it 'registers an offense for Time.parse' do
       expect_offense(<<~RUBY)
         Time.parse("2012-03-02 16:05:37")