Allow `pub install` and `pub update` to update dependers.

Allow `pub install` and `pub update` to update dependers.

If the pubspec has a new dependency which causes an incompatibility with the
locked packages' version constraints, `pub install` will now unlock packages
one by one until a compatible version graph can be found.

`pub update <package>` will now always update the given package to its latest
version, even if that requires updating locked packages that depend on it
transitively. If no amount of updating will make the latest version valid, an
exception will be thrown.

This was originally submitted as r10779

Committed: https://code.google.com/p/dart/source/detail?r=11119

[nweiz, 2012-08-21 18:26:46]

This is the same as r10779 except for patch set 2.

[Bob Nystrom, 2012-08-21 18:29:57]

Just reviewed patch set 2.

https://chromiumcodereview.appspot.com/10837274/diff/3004/utils/pub/version_s...
File utils/pub/version_solver.dart (right):

https://chromiumcodereview.appspot.com/10837274/diff/3004/utils/pub/version_s...
utils/pub/version_solver.dart:331: Dependency dependency, VersionConstraint
oldConstraint) {
(source, dep, constraint) is a PackageRef. Can we just pass one of those around
instead? Seems like it would make this a lot cleaner.

https://chromiumcodereview.appspot.com/10837274/diff/3004/utils/pub/version_s...
utils/pub/version_solver.dart:353: if (source == null) print("dependency for
null source: ${dependency.name}");
Debug code. Nix.

[nweiz, 2012-08-21 19:57:23]

https://chromiumcodereview.appspot.com/10837274/diff/3004/utils/pub/version_s...
File utils/pub/version_solver.dart (right):

https://chromiumcodereview.appspot.com/10837274/diff/3004/utils/pub/version_s...
utils/pub/version_solver.dart:331: Dependency dependency, VersionConstraint
oldConstraint) {
On 2012/08/21 18:29:57, Bob Nystrom wrote:
> (source, dep, constraint) is a PackageRef. Can we just pass one of those
around
> instead? Seems like it would make this a lot cleaner.

Calling these values a PackageRef isn't really an accurate description of what's
going on. [source] and [description] are just capturing the properties of
[dependency] in case removing a package ref from that caused them to be deleted.

A more semantic way to clean this up would be to pass in the old dependency as
well as the new dependency, so that's what I've done.

https://chromiumcodereview.appspot.com/10837274/diff/3004/utils/pub/version_s...
utils/pub/version_solver.dart:353: if (source == null) print("dependency for
null source: ${dependency.name}");
On 2012/08/21 18:29:57, Bob Nystrom wrote:
> Debug code. Nix.

Done.

[Bob Nystrom, 2012-08-21 21:01:04]

LGTM!