Fix #microseconds conversion and #fast_string_to_time

* Use direct integer parsing in #fast_string_to_time to avoid convoluted
   conversions and errors due to truncation.
 * Use Float#round in #microseconds to avoid truncation errors.

Signed-off-by: Michael Koziarski <michael@koziarski.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 520f3c8c0c..5e8a01644d 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -13,6 +13,7 @@ module ActiveRecord
       module Format
         ISO_DATE = /\A(\d{4})-(\d\d)-(\d\d)\z/
         ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(\.\d+)?\z/
+        NEW_ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(?:\.(\d+))?\z/
       end
 
       attr_reader :name, :default, :type, :limit, :null, :sql_type, :precision, :scale
@@ -167,10 +168,11 @@ module ActiveRecord
         end
 
         protected
-          # '0.123456' -> 123456
-          # '1.123456' -> 123456
+          # Rational(123456, 1_000_000) -> 123456
+          # The sec_fraction component returned by Date._parse is a Rational fraction of a second or nil
+          # NB: This method is optimized for performance by immediately converting away from Rational.
           def microseconds(time)
-            ((time[:sec_fraction].to_f % 1) * 1_000_000).to_i
+            ((time[:sec_fraction].to_f % 1) * 1_000_000).round
           end
 
           def new_date(year, mon, mday)
@@ -194,9 +196,8 @@ module ActiveRecord
 
           # Doesn't handle time zones.
           def fast_string_to_time(string)
-            if string =~ Format::ISO_DATETIME
-              microsec = ($7.to_f * 1_000_000).to_i
-              new_time $1.to_i, $2.to_i, $3.to_i, $4.to_i, $5.to_i, $6.to_i, microsec
+            if md = Format::NEW_ISO_DATETIME.match(string)
+              new_time *md.to_a[1..7].map(&:to_i)
             end
           end