From: Brian Candler <B.Candler@...>
Date: 2003-03-22T19:30:40+09:00
Subject: Re: Rake problem?

On Sat, Mar 22, 2003 at 09:23:21AM +0900, Jim Weirich wrote:
> Apply the attached patch to correct Rakefile1.
...
> --- Rakefile1	19 Mar 2003 12:48:05 -0000	1.1
> +++ Rakefile1	21 Mar 2003 23:47:43 -0000
> @@ -17,9 +17,10 @@
>    Sys.run "gcc #{src} -c -o #{t.name}"
>  end
>  
> -task :obj => ["a.o", "b.o", "main.o"]
> +OBJFILES = ["a.o", "b.o", "main.o"]
> +task :obj => OBJFILES
>  
> -file "main" => [:obj] do |t|
> +file "main" => OBJFILES do |t|
>    Sys.run "gcc -o #{t.name} main.o a.o b.o"
>  end

With rake-0.2.1 I can't duplicate the original problem, i.e. I can set it
back to "main" => [:obj] and it works:

$ rm main
$ rake
(in /v/build/rake-0.2.1/doc/example)
gcc -o main main.o a.o b.o
$ rake
(in /v/build/rake-0.2.1/doc/example)
$ 

However, where you have

>    Sys.run "gcc -o #{t.name} main.o a.o b.o"

I thought it might be better to put

    Sys.run "gcc -o #{t.name} #{OBJFILES.join(' ')}"

since you've factored out the filenames anyway. The syntax is somehow
unattractive. Assuming you keep 'file "main" => OBJFILES' then I notice you
can do

  #{t.prerequisites.join(' ')}

but that won't work in the general case where the dependencies may come in
groups (say .o files and .a files) which need handling differently.

Hmm, how about some sugar:
  #{t.sources('.o')}

i.e. the first parameter is a suffix or regex, and an optional second
parameter if you want to join with something other than space. But if you
set "main" => [:obj] instead of "main" => OBJFILES then it would need to
traverse a level down to find the actual source files.

One other idea. If you have a large project with components in
subdirectories, it would be really cool if you could have a top-level
Rakefile which includes the sub-Rakefiles and generates a single dependency
graph automatically. As far as I can see all you would need is something
like

    require 'subdir/Rakefile'

except that all the files/dependencies would need 'subdir' prepended to them
in the global dependency graph (perhaps using a global $prefix). Or maybe the
graph should be built with only absolute pathnames in it? so
    file "foo"
would generate basename($0)+"foo" ?

There's an excellent article here about why this could work extremely well
for large projects:
http://www.tip.net.au/~millerp/rmch/recu-make-cons-harm.html

Regards,

Brian.

P.S. I'm not sure I like the searching for Rakefile in parent directories.
If I am in doc/example and type 'rake' then I get the testsuite built; it's
a bit unexpected!