Clean up code that locates SDK and SDK version.

Clean up code that locates SDK and SDK version.

This is prep work for SDK constraints. It moves the SDK
version-related code out of SdkSource (which will go away at some
point) into its own library.

I also removed the need for the DART_SDK env variable. It will
still be used if set (which the tests need), but if not set, Pub 
will locate the SDK.
Clean up a few static warnings.

Committed: https://code.google.com/p/dart/source/detail?r=17433

[nweiz, 2013-01-19 00:35:47]

lgtm

https://codereview.chromium.org/11871028/diff/1/pkg/path/lib/path.dart
File pkg/path/lib/path.dart (right):

https://codereview.chromium.org/11871028/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:170: if (args[i] != null && args[i - 1] == null) {
Short-circuit?

https://codereview.chromium.org/11871028/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:181: .mappedBy((arg) => arg == null ? "null" : '"$arg"')
I really wish we had a better way of dumping strings than '"$arg"'. That's so
hard to read if it contains a newline or a quote or anything.

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart
File utils/pub/sdk.dart (right):

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart#newcode27
utils/pub/sdk.dart:27: return dir;
I wonder if we should do some sanity checks here so that we can throw a
reasonable error message if the directory we think contains the SDK actually
doesn't.

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart#newcode36
utils/pub/sdk.dart:36: var revision = new File(revisionPath).readAsStringSync();
Oh synchronous file IO, how lovely you are...

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart#newcode37
utils/pub/sdk.dart:37: return new Version.parse("0.0.0-r.${revision.trim()}");
Another place it would be good to do some validation. We could even print some
instructions on what to do if we've found the SDK but it didn't contain a
revision file.

[Bob Nystrom, 2013-01-22 23:53:18]

Thanks!

https://codereview.chromium.org/11871028/diff/1/pkg/path/lib/path.dart
File pkg/path/lib/path.dart (right):

https://codereview.chromium.org/11871028/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:170: if (args[i] != null && args[i - 1] == null) {
On 2013/01/19 00:35:47, nweiz wrote:
> Short-circuit?

Done.

https://codereview.chromium.org/11871028/diff/1/pkg/path/lib/path.dart#newcod...
pkg/path/lib/path.dart:181: .mappedBy((arg) => arg == null ? "null" : '"$arg"')
On 2013/01/19 00:35:47, nweiz wrote:
> I really wish we had a better way of dumping strings than '"$arg"'. That's so
> hard to read if it contains a newline or a quote or anything.

Agreed. But until then, this should cover most cases.

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart
File utils/pub/sdk.dart (right):

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart#newcode27
utils/pub/sdk.dart:27: return dir;
On 2013/01/19 00:35:47, nweiz wrote:
> I wonder if we should do some sanity checks here so that we can throw a
> reasonable error message if the directory we think contains the SDK actually
> doesn't.

I don't think we've hit issues with this in the wild, at least not yet, so I'm
not too worried here.

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart#newcode36
utils/pub/sdk.dart:36: var revision = new File(revisionPath).readAsStringSync();
On 2013/01/19 00:35:47, nweiz wrote:
> Oh synchronous file IO, how lovely you are...

Oh yeah. I thought about making this async and then remembered that I don't
completely hate myself.

https://codereview.chromium.org/11871028/diff/1/utils/pub/sdk.dart#newcode37
utils/pub/sdk.dart:37: return new Version.parse("0.0.0-r.${revision.trim()}");
On 2013/01/19 00:35:47, nweiz wrote:
> Another place it would be good to do some validation. We could even print some
> instructions on what to do if we've found the SDK but it didn't contain a
> revision file.

Ditto previous comment. I don't mind making this more robust over time but we
haven't seen too many issues here so far.