Add time zones support (crystal-lang#5324)

* Add cache for last zone to Time::Location#lookup

* Implement Time::Location including timezone data loader

Remove representation of floating time from `Time` (formerly expressed
as `Time::Kind::Unspecified`).

Floating time should not be represented as an instance of `Time` to avoid undefined operations through type safety (see crystal-lang#5332).
Breaking changes:
* Calls to `Time.new` and `Time.now` are now in the local time zone by
  default.
* `Time.parse`, `Time::Format.new` and `Time::Format.parse` don't specify a default location.
  If none is included in the time format and no default argument is provided, the parse method wil raise an exception because there is no way to know how such a value should be represented as an instance of `Time`.
  Applications expecting time values without time zone should provide default location to apply in such a case.

* Implement custom zip file reader to remove depenencies

* Add location cache for `Location.load`

* Rename `Location.local` to `.load_local` and make `local` a class property

* Fix env ZONEINFO

* Fix example code string representation of local Time instance

* Time zone implementation for win32

This adds basic support for using the new time zone model on windows.
* `Crystal::System::Time.zone_sources` returns an empty array because
  Windows does not include a copy of the tz database.
* `Crystal::System::Time.load_localtime` creates a local time zone
  `Time::Location` based on data provided by `GetTimeZoneInformation`.
* A mapping from Windows time zone names to identifiers used by the
  IANA timezone database is included as well as an automated generator
  for that file.

* Add stubs for methods with file acces

Trying to load a location from a file will fail because `File` is not
yet ported to windows.

scripts/generate_windows_zone_names.cr

@@ -0,0 +1,76 @@
+# This script generates the file src/crystal/system/win32/zone_names.cr
+# that contains mappings for windows time zone names based on the values
+# found in http://unicode.org/cldr/data/common/supplemental/windowsZones.xml
+
+require "http/client"
+require "xml"
+require "../src/compiler/crystal/formatter"
+
+WINDOWS_ZONE_NAMES_SOURCE = "http://unicode.org/cldr/data/common/supplemental/windowsZones.xml"
+TARGET_FILE               = File.join(__DIR__, "..", "src", "crystal", "system", "win32", "zone_names.cr")
+
+response = HTTP::Client.get(WINDOWS_ZONE_NAMES_SOURCE)
+
+# Simple redirection resolver
+# TODO: Needs to be replaced by proper redirect handling that should be provided by `HTTP::Client`
+if (300..399).includes?(response.status_code) && (location = response.headers["Location"]?)
+  response = HTTP::Client.get(location)
+end
+
+xml = XML.parse(response.body)
+
+nodes = xml.xpath_nodes("/supplementalData/windowsZones/mapTimezones/mapZone[@territory=001]")
+
+entries = [] of {key: String, zones: {String, String}, tzdata_name: String}
+
+nodes.each do |node|
+  location = Time::Location.load(node["type"])
+  next unless location
+  time = Time.now(location).at_beginning_of_year
+  zone1 = time.zone
+  zone2 = (time + 6.months).zone
+
+  if zone1.offset > zone2.offset
+    # southern hemisphere
+    zones = {zone2.name, zone1.name}
+  else
+    # northern hemisphere
+    zones = {zone1.name, zone2.name}
+  end
+
+  entries << {key: node["other"], zones: zones, tzdata_name: location.name}
+rescue err : Time::Location::InvalidLocationNameError
+  pp err
+end
+
+# sort by IANA database identifier
+entries.sort_by! &.[:tzdata_name]
+
+hash_items = String.build do |io|
+  entries.each do |entry|
+    entry[:key].inspect(io)
+    io << " => "
+    entry[:zones].inspect(io)
+    io << ", # " << entry[:tzdata_name] << "\n"
+  end
+end
+
+source = <<-CRYSTAL
+  # This file was automatically generated by running:
+  #
+  #   scripts/generate_windows_zone_names.cr
+  #
+  # DO NOT EDIT
+
+  module Crystal::System::Time
+    # These mappings for windows time zone names are based on
+    # #{WINDOWS_ZONE_NAMES_SOURCE}
+    WINDOWS_ZONE_NAMES = {
+      #{hash_items}
+    }
+  end
+  CRYSTAL
+
+source = Crystal.format(source)
+
+File.write(TARGET_FILE, source)

spec/std/file_spec.cr

@@ -1033,8 +1033,8 @@ describe "File" do
       filename = "#{__DIR__}/data/temp_write.txt"
       File.write(filename, "")
 
-      atime = Time.new(2000, 1, 2)
-      mtime = Time.new(2000, 3, 4)
+      atime = Time.utc(2000, 1, 2)
+      mtime = Time.utc(2000, 3, 4)
 
       File.utime(atime, mtime, filename)
 
@@ -1046,8 +1046,8 @@ describe "File" do
     end
 
     it "raises if file not found" do
-      atime = Time.new(2000, 1, 2)
-      mtime = Time.new(2000, 3, 4)
+      atime = Time.utc(2000, 1, 2)
+      mtime = Time.utc(2000, 3, 4)
 
       expect_raises Errno, "Error setting time to file" do
         File.utime(atime, mtime, "#{__DIR__}/nonexistent_file")
@@ -1069,7 +1069,7 @@ describe "File" do
 
     it "sets file times to given time" do
       filename = "#{__DIR__}/data/temp_touch.txt"
-      time = Time.new(2000, 3, 4)
+      time = Time.utc(2000, 3, 4)
       begin
         File.touch(filename, time)
 

spec/std/http/http_spec.cr

@@ -33,7 +33,7 @@ describe HTTP do
   it "parses and is local (#2744)" do
     date = "Mon, 09 Sep 2011 23:36:00 -0300"
     parsed_time = HTTP.parse_time(date).not_nil!
-    parsed_time.local?.should be_true
+    parsed_time.offset.should eq -3 * 3600
     parsed_time.to_utc.to_s.should eq("2011-09-10 02:36:00 UTC")
   end
 
@@ -44,16 +44,8 @@ describe HTTP do
     end
 
     it "with local time zone" do
-      tz = ENV["TZ"]?
-      ENV["TZ"] = "Europe/Berlin"
-      LibC.tzset
-      begin
-        time = Time.new(1994, 11, 6, 8, 49, 37, nanosecond: 0, kind: Time::Kind::Local)
-        HTTP.rfc1123_date(time).should eq(time.to_utc.to_s("%a, %d %b %Y %H:%M:%S GMT"))
-      ensure
-        ENV["TZ"] = tz
-        LibC.tzset
-      end
+      time = Time.new(1994, 11, 6, 8, 49, 37, nanosecond: 0, location: Time::Location.load("Europe/Berlin"))
+      HTTP.rfc1123_date(time).should eq(time.to_utc.to_s("%a, %d %b %Y %H:%M:%S GMT"))
     end
   end
 

spec/std/json/mapping_spec.cr

@@ -252,7 +252,7 @@ describe "JSON mapping" do
   it "parses json with Time::Format converter" do
     json = JSONWithTime.from_json(%({"value": "2014-10-31 23:37:16"}))
     json.value.should be_a(Time)
-    json.value.to_s.should eq("2014-10-31 23:37:16")
+    json.value.to_s.should eq("2014-10-31 23:37:16 UTC")
     json.to_json.should eq(%({"value":"2014-10-31 23:37:16"}))
   end