From: "James M. Lawrence" <quixoticsycophant@...>
Date: 2008-09-25T09:18:49+09:00
Subject: Re: Rake dependencies unknown prior to running tasks

Joe W旦lfel wrote:
> I didn't say what was being built couldn't be determined
> programmatically.  I said it couldn't be determined until certain
> portions were already built.  To build those things initial things I
> need a build tool, such as Rake.  If the suggestion is that I
> shouldn't actually execute any Rake tasks until after I've determined
> all possible tasks then the catch 22 your talking about actually
> occurs.  The only practical solution I've come up with so far is to
> have Rake build the initial targets and then call itself again to
> determine the rest of the dependency graph and build the remaining
> targets.   If there were a way to augment the initial dependency
> graph dynamically then this wouldn't be necessary.   I just don't
> happen to know of one.

If you really cannot know what is going to be built, for example if a 
program generates files whose names are taken from /dev/random and then 
other tasks depend on those files, then you are in a pickle.  Normally 
this kind of thing is handled by 'import', but this assumes tasks can be 
determined (for example examining the makedepend output).

What do you think of this:

  task :setup_a do
    puts "setup_a"
  end

  task :setup_b do
    puts "setup_b"
  end

  task :setup => [:setup_a, :setup_b] do
    puts "setup phase complete. defining new tasks..."

    task :main_a do
      puts "main_a"
    end

    task :main_b do
      puts "main_b"
    end

    puts "restarting..."
    throw :restart
  end

  task :main => [:main_a, :main_b] do
    puts "main phase complete."
  end
  task :main_a => :setup
  task :main_b => :setup

  task :default => :main do
    puts "all done."
  end

% rake -f test/Rakefile.restart-flag
(in /Users/jlawrence/work/rake)
setup_a
setup_b
setup phase complete. defining new tasks...
restarting...
main_a
main_b
main phase complete.
all done.

I may be inflicting hardship on myself since this would complicate drake 
(http://drake.rubyforge.org), but anyway...  This patch is for regular 
rake; the git branch is the same thing.

  % git clone git://github.com/quix/rake.git
  % cd rake
  % git checkout -b restart-flag origin/restart-flag

diff --git a/lib/rake.rb b/lib/rake.rb
index 7c84f57..3010261 100755
--- a/lib/rake.rb
+++ b/lib/rake.rb
@@ -560,8 +560,15 @@ module Rake

     # Invoke the task if it is needed.  Prerequites are invoked first.
     def invoke(*args)
-      task_args = TaskArguments.new(arg_names, args)
-      invoke_with_call_chain(task_args, InvocationChain::EMPTY)
+      catch(:done) {
+        loop {
+          catch(:restart) {
+            task_args = TaskArguments.new(arg_names, args)
+            invoke_with_call_chain(task_args, InvocationChain::EMPTY)
+            throw :done
+          }
+        }
+      }
     end

     # Same as invoke, but explicitly pass a call chain to detect
@@ -573,8 +580,8 @@ module Rake
           puts "** Invoke #{name} #{format_trace_flags}"
         end
         return if @already_invoked
-        @already_invoked = true
         invoke_prerequisites(task_args, new_chain)
+        @already_invoked = true
         execute(task_args) if needed?
       end
     end





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