Isolate.resolvePackageUri has inconsistent behavior when called from a script launched via relative path

[jcollins-g]

When running in the VM with preview-dart-2, resolvePackageUri sometimes doesn't resolve to a file URI correctly unless the script was launched with an absolute path.

demo:

/tmp/resolve
$ cat pubspec.yaml
name: resolvedemo
version: 0.1.0
/tmp/resolve
$ pub get
Resolving dependencies... 
Got dependencies!
/tmp/resolve
$ cat bin/resolve.dart 
import "dart:isolate" show Isolate;

main() {
  Uri theUri = Uri.parse('package:resolvedemo/test.dart');
  print('theUri: $theUri');
  Isolate.resolvePackageUri(theUri).then((u) => print ('resolved Uri: $u'));
}

/tmp/resolve
$ dart `pwd`/bin/resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: file:///tmp/resolve/lib/test.dart
/tmp/resolve
$ dart bin/resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: file:///tmp/resolve/lib/test.dart
/tmp/resolve
$ dart --preview-dart-2 `pwd`/bin/resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: file:///tmp/resolve/lib/test.dart
/tmp/resolve
$ dart --preview-dart-2 bin/resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: lib/test.dart
/tmp/resolve
$

I believe all four runs of the program should have the same output.
(edit: refined example for clarity)

[jcollins-g]

This seems to be substantially worse on windows, with the resolution failing completely in all cases:

[jcollins-g]

This blocks dart-lang/dartdoc#1668.

[lrhn]

The behavior is correct, but it might not be useful.

The location of the .packages file is found relative to the entry point. There is no specification of what the result of that is, just that it finds the file, so choosing a relative path for the location of the .packages file is not wrong.
The .packages file contains a relative location that is interpreted as relative to the .packages file.
So, when the entry-point is relative, everything after that stays relative.

I think we should just decide that the path of the .packages file must be resolved into an absolute URI before resolving a relative path against it. That would likely be done by resolving the relative URI against the current working directory (aka, Uri.base). That would avoid resolving a relative URI against another relative URI, which is generally a code smell.

[jcollins-g]

@lrhn Resolving to an absolute file URI would work for me. Also I'll mention that I don't think returning null here is correct on Windows -- no matter what we decide, that should be fixed.

[lrhn]

Returning null does seem like a bug.

[jcollins-g]

The returning null on Windows is still a blocking bug for Dartdoc under Dart 2.0.

[srawlins]

I get null on Macos if I am in a directory below the .packages file. With the same layout as @jcollins-g 's above:

$ cd bin/

$ pwd
/tmp/resolve/bin

$ dart `pwd`/resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: file:///tmp/resolve/lib/test.dart

$ dart resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: file:///private/tmp/resolve/lib/test.dart

$ dart --preview-dart-2 `pwd`/resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: file:///tmp/resolve/lib/test.dart

$ dart --preview-dart-2 resolve.dart
theUri: package:resolvedemo/test.dart
resolved Uri: null

The second example returns file:///private/tmp/resolve/lib/test.dart, a bit of a head scratcher..., and the fourth example returns null. ☹️

[a-siva]

I am able to reproduce the behavior that @srawlins reports on linux too.

[a-siva]

https://dart-review.googlesource.com/c/sdk/+/56622 should fix this.