Get rid of RootSource.

Get rid of RootSource.

This was a sort of hackish source only used internally during
version solving. But it causes a couple of subtle bugs because it
never gets registered with the SourceRegistry. That in turn makes
toString() fail on any PackageId with that source since it relies
on the Source being registered.

The simplest fix is to just remove the hacked source and have a
null source in PackageId/Ref mean "root" and handle it specially.

Committed: https://code.google.com/p/dart/source/detail?r=17646

[Bob Nystrom, 2013-01-24 22:18:40]

Hey, Nathan is on vacation. Want to be a pub reviewer?

[Jennifer Messerly, 2013-01-24 23:24:37]

lgtm

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart
File utils/pub/package.dart (right):

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart#newcode86
utils/pub/package.dart:86: /// this is a root package ID, this will be `null`.
fwiw, I think Kathy suggested not using code font for `null`, as a general
desire to avoid too much code font. Up to you though. I might be misremembering
this.

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart#newcod...
utils/pub/package.dart:104: (source != null ? source.name.hashCode : 0) ^
Another idea here: you could make Source.hashCode return its name.hashCode:

    class Source { ...; int get hashCode => name.hashCode; }

Then change this one to be:

    int get hashCode => name.hashCode ^ source.hashCode ^ version.hashCode


That might be cleaner? Basically, exploit the fact that "null.hashCode" works in
Dart :)

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart#newcod...
utils/pub/package.dart:113: other.source == source &&
just checking, source already implements reasonable equality operator? Or do we
know that identity semantics work for it?

[Bob Nystrom, 2013-01-25 18:22:50]

Thanks!

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart
File utils/pub/package.dart (right):

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart#newcode86
utils/pub/package.dart:86: /// this is a root package ID, this will be `null`.
On 2013/01/24 23:24:37, John Messerly wrote:
> fwiw, I think Kathy suggested not using code font for `null`, as a general
> desire to avoid too much code font. Up to you though. I might be
misremembering
> this.

I think you're remembering right, though I personally do prefer using code font
for literals. I like a little visual style variation and I think code font can
be important to disambiguate use-mention in cases where a literal is a valid
word like "this".

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart#newcod...
utils/pub/package.dart:104: (source != null ? source.name.hashCode : 0) ^
On 2013/01/24 23:24:37, John Messerly wrote:
> Another idea here: you could make Source.hashCode return its name.hashCode:
> 
>     class Source { ...; int get hashCode => name.hashCode; }
> 
> Then change this one to be:
> 
>     int get hashCode => name.hashCode ^ source.hashCode ^ version.hashCode
> 
> 
> That might be cleaner? Basically, exploit the fact that "null.hashCode" works
in
> Dart :)

Great idea! Done.

https://codereview.chromium.org/12047096/diff/1/utils/pub/package.dart#newcod...
utils/pub/package.dart:113: other.source == source &&
On 2013/01/24 23:24:37, John Messerly wrote:
> just checking, source already implements reasonable equality operator? Or do
we
> know that identity semantics work for it?

I'm relying on identity here. Sources are effectively singletons and weird
things would happen if you had more than one source of the same type.