Wednesday, September 12, 2012

New pub package layout

Today, Bob Nystrom, one of the pub engineers, posted details about the new pub package layout. Time to use the new layout for your packages!

Bob writes:


If you live on bleeding_edge, pub now supports the new package layout conventions that avoid the nasty circular symlinks.

Pub also still supports the old style too, simultaneously. It works like this:
  1. When pub is generating a symlink to a package it determines if it's an old style or new style package. The presence of a .dart file at the top level (aside from build.dart) indicates that it's an old style package.
  2. If it's an old style package, pub symlinks to the package's root directory.
  3. If it's a new style package, it looks for a "lib" directory inside that package and symlinks to that.
  4. It will also generate a self link, but only for new style packages.
So, if you have:

myapp/
  pubspec.yaml -> depends on old_style and new_style
  lib/
    app.dart

old_style/
  old_style.dart

new_style/
  lib/
    new_style.dart

You run "pub install" on myapp, and you'll get:

myapp/
  pubspec.yaml -> depends on old_style and new_style
  lib/
    app.dart
  packages/
    myapp/ -> symlink to myapp/lib/
      app.dart
    old_style/ -> symlink to old_style/
      old_style.dart
    new_style/ -> symlink to new_style/lib/
      new_style.dart

Note that inside packages/ everything looks like you want and your imports should be unchanged. What this means is that if some package you depend on migrates from the old to the new style, it's shouldn't affect you. The next time you update that package, it will magically do the right thing.

All of the SDK packages that come with Dart are still using the old style, but we'll be updating those over the next couple of weeks. Around M1, I will remove support for the old layout. If you haven't updated your package by then, it will stop working.

Let me know if you have questions/comments/complaints/sonnets. You can read more about the pub package layout recommendation.


As always, you can join the discussion at the Dart mailing list, and post questions to Stack Overflow.