Fix #5233: Increase our ability to detect Windows.

This increases our ability to detect Windows, and to detect Windows+Bash.  It also adds a message to Windows for users who try to "--watch", also noting to to them to check out the Windows ticket so eventually somebody pings us if this issue is fixed. /cc @TAGraves

lib/jekyll/commands/build.rb

@@ -71,12 +71,23 @@ module Jekyll
         #
         # Returns nothing.
         def watch(site, options)
+          if Utils::Platforms.windows?
+            Jekyll.logger.warn "", "--watch arg is unsupported on Windows. "
+            Jekyll.logger.warn "", "If you are on Windows Bash, please see: " \
+              "https://github.com/Microsoft/BashOnWindows/issues/216"
+
+          else
             External.require_with_graceful_fail "jekyll-watch"
             watch_method = Jekyll::Watcher.method(:watch)
             if watch_method.parameters.size == 1
-            watch_method.call(options)
+              watch_method.call(
+                options
+              )
             else
-            watch_method.call(options, site)
+              watch_method.call(
+                options, site
+              )
+            end
           end
         end
       end # end of class << self

lib/jekyll/utils/platforms.rb

@@ -13,18 +13,55 @@ module Jekyll
         end
       end
 
+      # --
+      # Allows you to detect "real" Windows, or what we would consider
+      # "real" Windows.  That is, that we can pass the basic test and the
+      # /proc/version returns nothing to us.
+      # --
+
+      def really_windows?
+        RbConfig::CONFIG["host_os"] =~ %r!mswin|mingw|cygwin!i && \
+          !proc_version
+      end
+
+      #
+
+      def windows?
+        RbConfig::CONFIG["host_os"] =~ %r!mswin|mingw|cygwin!i || \
+          proc_version =~ %r!microsoft!i
+      end
+
+      #
+
+      def linux?
+        RbConfig::CONFIG["host_os"] =~ %r!linux! && \
+          proc_version !~ %r!microsoft!i
+      end
+
       # Provides windows?, linux?, osx?, unix? so that we can detect
       # platforms. This is mostly useful for `jekyll doctor` and for testing
       # where we kick off certain tests based on the platform.
 
-      { :windows? => %r!mswin|mingw|cygwin!, :linux? => %r!linux!, \
+      { :osx? => %r!darwin|mac os!, :unix? => %r!solaris|bsd! }.each do |k, v|
-          :osx? => %r!darwin|mac os!, :unix? => %r!solaris|bsd! }.each do |k, v|
         define_method k do
           !!(
             RbConfig::CONFIG["host_os"] =~ v
           )
         end
       end
+
+      #
+
+      private
+      def proc_version
+        @cached_proc_version ||= begin
+          Pathutil.new(
+            "/proc/version"
+          ).read
+        rescue Errno::ENOENT
+          nil
+        end
+      end
     end
   end
 end