Clean up the semantics of io.dart operations w.r.t. symlinks.

Clean up the semantics of io.dart operations w.r.t. symlinks.

fileExists and dirExists will now both return true for symlinks only if those
symlinks are unbroken and point to entries of the appropriate type. entryExists
will return true for any symlink as well, broken or unbroken.

deleteDir and deleteFile have been replaced with a single function, deleteEntry.
This will delete whatever filesystem entry exists at the path specified, whether
it's a file, directory, or symlink (broken or unbroken).

BUG=9454
Committed: https://code.google.com/p/dart/source/detail?r=20575

[Bob Nystrom, 2013-03-27 20:10:09]

It would be really great to have tests in io_test for all of the permutations of
{file|dir|link}Exists against files, directories, links, etc.

Two questions, otherwise, LGTM. Let me know when this is in and I'll sync it and
see if it fixes the listing issue too.

https://codereview.chromium.org/13116020/diff/1/utils/pub/entrypoint.dart
File utils/pub/entrypoint.dart (right):

https://codereview.chromium.org/13116020/diff/1/utils/pub/entrypoint.dart#new...
utils/pub/entrypoint.dart:213: if (!entryExists(lockFilePath)) return new
LockFile.empty();
Shouldn't this stay fileExists()? It's going to do bad things if we try to load
a directory as a lockFile.

https://codereview.chromium.org/13116020/diff/1/utils/pub/oauth2.dart
File utils/pub/oauth2.dart (right):

https://codereview.chromium.org/13116020/diff/1/utils/pub/oauth2.dart#newcode69
utils/pub/oauth2.dart:69: if (entryExists(credentialsFile))
deleteEntry(credentialsFile);
Why entryExists here?

[nweiz, 2013-03-27 20:36:28]

I've added tests for the existence predicates.

https://codereview.chromium.org/13116020/diff/1/utils/pub/entrypoint.dart
File utils/pub/entrypoint.dart (right):

https://codereview.chromium.org/13116020/diff/1/utils/pub/entrypoint.dart#new...
utils/pub/entrypoint.dart:213: if (!entryExists(lockFilePath)) return new
LockFile.empty();
On 2013/03/27 20:10:09, Bob Nystrom wrote:
> Shouldn't this stay fileExists()? It's going to do bad things if we try to
load
> a directory as a lockFile.

It's also going to do bad things if we try to write a lock file to a directory.
If "pubspec.lock" isn't a file, installation will fail regardless; this just
makes it fail faster.

https://codereview.chromium.org/13116020/diff/1/utils/pub/oauth2.dart
File utils/pub/oauth2.dart (right):

https://codereview.chromium.org/13116020/diff/1/utils/pub/oauth2.dart#newcode69
utils/pub/oauth2.dart:69: if (entryExists(credentialsFile))
deleteEntry(credentialsFile);
On 2013/03/27 20:10:09, Bob Nystrom wrote:
> Why entryExists here?

If, through some weird fluke or user craziness, "credentials.json" is a
directory or broken symlink, we don't want that to break pub.

[nweiz, 2013-03-27 20:38:04]

Committed patchset #2 manually as r20575 (presubmit successful).