Try to give nicer error messages on internal failures

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@5111 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rdoc/parsers/parse_rb.rb

@@ -1393,7 +1393,23 @@ module RDoc
       @unget_read = []
       @read = []
       catch(:eof) do
-        parse_statements(@top_level)
+        begin
+          parse_statements(@top_level)
+        rescue Exception => e
+          $stderr.puts "\n\n"
+          $stderr.puts "RDoc failure in #@input_file_name at or around " +
+                       "line #{@scanner.line_no} column #{@scanner.char_no}"
+          $stderr.puts 
+          $stderr.puts "Before reporting this, could you check that the file"
+          $stderr.puts "you're documenting compiles cleanly--RDoc is not a"
+          $stderr.puts "full Ruby parser, and gets confused easily if fed"
+          $stderr.puts "invalid programs."
+          $stderr.puts
+          $stderr.puts "The internal error was:\n\n"
+          
+          e.set_backtrace(e.backtrace[0,4])
+          raise
+        end
       end
       @top_level
     end