Releases: Variablize Release Notes

Add additional variables to the release note files to allow setting the
version number and date.  The version number is required, and can be
used to automatically set the release notes title.  The date is optional
and can be set hours/days after the release.

Additionally, a Makefile test is added that checks whether the download
files exist on the Bitcoin.org server.  This can help prevent creating a
broken Download page.

* Set variables for all previous releases

* Document variables in README.md

* Update code and templates to use variables

* Add the Download page links to the "dl" CSS class. Also add newlines
  to make the HTML a bit easier to parse using sed

* Add a new Liquid plugin to print warnings. This is used to print a
  non-error warning if any release is created without the optional date

_plugins/releases.rb

@@ -5,46 +5,58 @@
 #and assign them the 'release' category.
 
 #This is later used to loop through site.pages in order
-#to display the release's list in chronological order, both
+#to display the release's list in version order, both
 #on the "Version history" page and RSS file.
 
-#This plugin also set site.DOWNLOAD_VERSION to the latest
-#available version of Bitcoin Core, which is used everywhere
-#in the download page.
-
-#Alias redirection pages are generated in /releases to avoid
-#breaking previous links in various websites.
+# This plugin also finds the highest required_version of
+# Bitcoin Core and populates the Download page with variables set in
+# that release file
 
 require 'yaml'
 
 module Jekyll
-  
+
   class ReleasePage < Page
 
-    def initialize(site, base, lang, srcdir, src, dstdir, dst, year, month, day)
+    def initialize(site, base, lang, srcdir, src, output_directory)
       @site = site
       @base = base
-      @dir = '/'+dstdir
-      @name = dst.gsub('.md','.html')
-      self.process(dst)
+      @dir = '/' + output_directory
+
+      ## Read in the file's YAML header
       self.read_yaml(File.join(base, srcdir), src)
-      self.data['lang'] = lang
-      self.data['date'] = year + '-' + month + '-' + day
-      self.data['version'] = dst.gsub('.md','').gsub(/[a-z]/,'')
-      self.data['versionint'] = versiontoint(self.data['version'])
-      self.data['layout'] = 'release'
-      if dstdir.index('/releases/') === 0
-        self.data['redirect'] = '/en/release/' + dst.gsub('.md','')
-        self.data['layout'] = 'redirect'
+
+      ## Die if required_ variables aren't set
+      if self.data['required_version']
+        version = self.data['required_version']
       else
-        self.data['category'] = 'release'
-        if !site.config.has_key?('DOWNLOAD_VERSION') or site.config['DOWNLOAD_VERSIONINT'] < self.data['versionint']
-          site.config['DOWNLOAD_VERSIONINT'] = self.data['versionint']
-          site.config['DOWNLOAD_VERSION'] = self.data['version']
-          site.config.delete('DOWNLOAD_MAGNETLINK') if site.config.has_key?('DOWNLOAD_MAGNETLINK')
-          site.config['DOWNLOAD_MAGNETLINK'] = self.data['magnetlink'] if self.data.has_key?('magnetlink')
-        end
-        site.pages << ReleasePage.new(site, base, lang, srcdir, src, '/releases/' + year + '/' + month + '/' + day, dst, year, month, day)
+        abort("Error: Variable required_version not set when processing " + src)
+      end
+
+      ## Output file is v<version>.md (converted later to HTML)
+      output_file = "v" + version + ".md"
+      @name = output_file
+      self.process(output_file)
+
+      ## Title required for <title></title> in _layouts/base.html
+      self.data['title'] = self.data['optional_title'] ? self.data['optional_title'] : "Bitcoin Core version %v released"
+      self.data['title'].gsub!('%v', version)
+
+      ## For translation, but currently always set to "en"
+      self.data['lang'] = lang
+
+      ## Only processes numeric version numbers with up to five decimals
+      self.data['versionint'] = versiontoint(self.data['required_version'])
+
+      self.data['layout'] = 'release'
+      self.data['category'] = 'release'
+
+      ## If this is the highest version we've seen so far...
+      if !site.config.has_key?('DOWNLOAD_VERSION') or site.config['DOWNLOAD_VERSIONINT'] < self.data['versionint']
+        site.config['DOWNLOAD_VERSIONINT'] = self.data['versionint']
+        site.config['DOWNLOAD_VERSION'] = self.data['required_version']
+
+        site.config['DOWNLOAD_MAGNETLINK'] = self.data['optional_magnetlink'] ? self.data['optional_magnetlink'] : nil
       end
     end
 
@@ -73,18 +85,9 @@ module Jekyll
         next if file == '.' or file == '..'
         lang = 'en'
         src = file
-        dst = file.split('-')
-        next if dst.length < 4
-        year = dst.shift()
-        month = dst.shift()
-        day = dst.shift()
-        next if !/^[0-9]{4}$/.match(year)
-        next if !/^[0-9]{2}$/.match(month)
-        next if !/^[0-9]{2}$/.match(day)
-        dst = dst.join('-')
         srcdir = '_releases'
-        dstdir = lang + '/release'
-        site.pages << ReleasePage.new(site, site.source, lang, '_releases', src, dstdir, dst, year, month, day)
+        output_directory = lang + '/release'
+        site.pages << ReleasePage.new(site, site.source, lang, '_releases', src, output_directory)
       end
       #TODO releases are only generated for english language,
       #but they could also be translated at some point. They would however