From: Joel VanderWerf <vjoel@...>
Date: 2006-03-21T03:05:21+09:00
Subject: Re: rake rules with multiple prerequisites

Jim Weirich wrote:
> Joel VanderWerf wrote:
>> Is it possible to have a rule which has a prerequisite specified by a
>> proc and also a FileList? I can use several procs, as a workaround:
>>
>> generic_files = [proc {"foo"}, proc {"bar"}, proc {"baz"}]
>> rule /^site_\w+/ => [
>>   proc {|fn| site_cfg_file(fn)},
>>   *generic_files
>> ] do ... end
>>
>>
>> But it would be nice to use a FileList. However, when I try
>>
>> generic_files = FileList["foo", "bar", "baz"]
>>
>> rake says it doesn't know how to build the task.
>>
>> Is there a better way of doing this?
> 
> Actually that should work.  If rake is reporting that it cannot build 
> your task, then probably one of the prerequisites cannot be built. 
> Remember, your rule says that you can build a site_XXX file if the 
> following file (or rules to build the following files) exist: 
> site_cfg_file(fn), "foo", "bar" and "baz".  I would check to see if 
> "foo", "bar" and "baz" all exist.

Here's what happens in this example:

---------
generic_files = [proc {"foo"}, proc {"bar"}, proc {"baz"}]
#generic_files = FileList["foo", "bar", "baz"]

rule /^site_\w+/ => [
  proc {|fn| "__#{fn}"},
  *generic_files
] do |t|
  p t.name
end

task :__site_stuff

file "foo" do touch "foo"; end
file "bar" do touch "bar"; end
file "baz" do touch "baz"; end
---------

As it is, it works:

$ rake site_stuff
(in /home/vjoel/ruby/misc/rake)
touch foo
touch bar
touch baz
"site_stuff"

But when I flip comments on the first two lines, I get:

$ rake site_stuff --trace
(in /home/vjoel/ruby/misc/rake)
rake aborted!
Don't know how to build task 'site_stuff'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.0/lib/rake.rb:1287:in `[]'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.0/lib/rake.rb:300:in `[]'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.0/lib/rake.rb:1719:in `run'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.0/lib/rake.rb:1719:in `run'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.0/bin/rake:7
/usr/local/bin/rake:18

Furthermore, if I comment out the proc:

#  proc {|fn| "__#{fn}"},

(still using the FileList) then rake goes into a tailspin:

$ rake site_stuff --trace
(in /home/vjoel/ruby/misc/rake)
rake aborted!
Rule Recursion Too Deep: [site_stuff => site_stuff => site_stuff =>
site_stuff =.......


-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407