From: Stefan Lang <langstefan@...>
Date: 2005-09-03T03:10:13+09:00
Subject: Re: Rake: multiple prerequisites in rule?

On Friday 02 September 2005 16:42, Martin Honermeyer wrote:
[...]
> I tried writing a Rake task which should automagically recompile
> each template upon changing either the .html or the .plogic file.
> I've come up with the following:
>
> desc "Make ERB templates from Kwartz html and plogic files"
> SRC = FileList['app/views/**/*.html']
> OBJ = SRC.ext('rhtml')
> task :templates => [OBJ]
>
> rule '.rhtml' => ['.html'] do |t|
>   sh "kwartz -Rails -e -p #{t.source.ext('plogic')}
> --extract=content #{t.source} > #{t.name}"
> end
>
>
> This works. The problem is that the .rhtml is only regenerated when
> the .html changes. I tried adding the .plogic file as another
> prerequisite:
>
> rule '.rhtml' => ['.html', '.plogic'] do |t|
>
> That makes Rake say
>
> Too many dependents specified in rule .rhtml: [".html", ".plogic"]
>
>
> Apparently, it's not possible to have multiple prerequisites for a
> rule. Does anyone have a hint on this?

Rant allows you to give a block to create the prerequisite name(s)
on the fly. The following works with Rant:

############## Rantfile ############################################
desc "Make ERB templates from Kwartz html and plogic files"
SRC = FileList['app/views/**/*.html']
OBJ = SRC.sub_ext('rhtml')
task :templates => OBJ

rhtml_sources = lambda { |target|
    [target.sub_ext("html"), target.sub_ext("plogic")]
}
gen Rule, '.rhtml' => rhtml_sources do |t|
    sys "kwartz -Rails -e -p #{t.prerequisites[1]} --extract=content 
#{t.prerequisites[0]} > #{t.name}"
end
####################################################################

To convert the Rakefile to an Rantfile I've:
* replaced calls to `ext' with calls to `sub_ext'
* replaced `rule' with `gen Rule, '

HTH,
  Stefan