How do I Declare a Rake::PackageTask with Prerequisites?

Question

In Rake, I can use the following syntax to declare that task charlie requires tasks alpha and bravo to have been completed first.

task :charlie => [:alpha, :bravo]

This seems to work fine if charlie is a typical Rake task or a file task but I cannot figure out how to do this for a Rake::PackageTask. Here are the relevant parts of the rakefile so far:

require 'rake/packagetask'

file :package_jar => [:compile] do
   puts("Packaging library.jar...")
   # code omitted for brevity, but this bit works fine
end

Rake::PackageTask.new("library", "1.0") do |pt|
   puts("Packaging library distribution artefact...")
   pt.need_tar = true
   pt.package_files = ["target/library.jar"]
end
task :package => :package_jar

What's happening here is that, for a clean build, it complains that it doesn't "know how to build task 'target/library.jar'". I have to run rake package_jar from the command line manually to get it to work, which is a bit of a nuisance. Is there any way I can make package depend on package_jar?

For what it's worth, I am using Rake version 0.9.2.2 with Ruby 1.8.7 on Linux.

Answer 1

When you run rake package (without previously running anything else to create any needed files) Rake sees that the package task needs the file target/library.jar. Since this file doesn’t yet exist Rake checks to see if it knows how to create it. It doesn’t know of any rules that will create this file, so it fails with the error you see.

Rake does have a task that it thinks will create a file named package_jar, and that task in fact creates the file target/library.jar, but it doesn’t realise this.

The fix is to tell Rake exactly what file is created in the file task. Rake will then automatically find the dependency.

Change

file :package_jar => [:compile] do

to

file 'target/library.jar' => [:compile] do

and then remove the line

task :package => :package_jar

since package_jar no longer exists and Rake will find the dependency on the file by itself.

Answer 2

In general in rake, if you want to add a dependency to a task, you need that task's name. So you need to figure out the name of the actual rake task that Rake::PackageTask is registering.

The easiest way to do this is by running with --trace — it lists each task's name as it is executing.

(I believe the name of a buildr package task is the filename of the package it produces, but I don't remember for certain. Use --trace to find out.)

Answer 3

You can add a dependency to any task by writing,

someTask.enhance [other, tasks]

where other and tasks can be either task names or task objects.

So in your case, you could write:

library = Rake::PackageTask.new(...) do
  ...
end

task(:package).enhance([library])