Optimize `Jekyll::Utils.parse_date` (#8425)

Merge pull request 8425

benchmark/parse-date

@@ -0,0 +1,25 @@
+#!/usr/bin/env ruby
+
+require_relative '../lib/jekyll'
+require 'benchmark/ips'
+
+date = "2014-08-02 14:43:06 PDT".freeze
+time = Time.parse(date)
+
+Benchmark.ips do |x|
+  x.report('Time.parse') do
+    Time.parse(date)
+  end
+
+  x.report('localtime') do
+    Time.parse(date).localtime
+  end
+
+  x.report('localtime parsed') do
+    time.localtime
+  end
+
+  x.report('Utils.parse_date') do
+    Jekyll::Utils.parse_date(date)
+  end
+end

lib/jekyll/utils.rb

@@ -128,7 +128,8 @@ module Jekyll
     # Returns the parsed date if successful, throws a FatalException
     # if not
     def parse_date(input, msg = "Input could not be parsed.")
-      Time.parse(input).localtime
+      @parse_date_cache ||= {}
+      @parse_date_cache[input] ||= Time.parse(input).localtime
     rescue ArgumentError
       raise Errors::InvalidDateError, "Invalid date '#{input}': #{msg}"
     end