[pub] Unexpected behavior for sdk constraint solving with sdk 3.0.0 update

[annagrin]

The sdk constraint sdk: ">=2.18.0 <3.0.0" resolves, but sdk: ">=2.10.0 <3.0.0" does not with the current version of SDK 3.0.0-21.0.dev

Is it intentional? I would expect them both to fail to resolve.

Related: dart-lang/webdev#1824

pubscpec

name: _test
version: 1.0.0
description: >-
  A fake package used for testing weak null-safety.
publish_to: none

environment:
  sdk: ">=2.18.0 <3.0.0"

dependencies:
  intl: ^0.17.0
  path: ^1.6.1

dev_dependencies:
  build_runner: '>=1.6.2 <3.0.0'
  build_web_compilers: '>=2.12.0 <4.0.0'

Result

➜  _test git:(annagrin) dart pub upgrade
...
  watcher 1.0.2
  web_socket_channel 2.2.0
  yaml 3.1.1
No dependencies changed.
1 package has newer versions incompatible with dependency constraints.
Try `dart pub outdated` for more information.

pubspec

name: _test
version: 1.0.0
description: >-
  A fake package used for testing weak null-safety.
publish_to: none

environment:
  sdk: ">=2.10.0 <3.0.0"

dependencies:
  intl: ^0.17.0
  path: ^1.6.1

dev_dependencies:
  build_runner: '>=1.6.2 <3.0.0'
  build_web_compilers: '>=2.12.0 <4.0.0'

Result

➜  _test git:(annagrin) dart pub upgrade
Resolving dependencies...
The current Dart SDK version is 3.0.0-21.0.dev.

Because _test requires SDK version >=2.10.0 <3.0.0, version solving failed.

[parlough]

I believe <3.0.0 is treated the same as <4.0.0 when the lower bound is >= 2.12.0 (dart-lang/pana@9882d0e).

The cause of this resolution failure is because a lower bound below 2.12, in this case >=2.10.0, means that package does not support null safety which is required by Dart 3. See #3686 for more context on the resolution message.

[lrhn]

Correct. If code can run on Dart 2.10, which does not support null safe code at all, then it cannot run on Dart 3.0 which only supports null safe code. So any min-SDK of less than 2.12 means that the code is definitely not compatible with Dart 3.0.

Treating <3.0.0 as <4.0.0 is just to avoid everybody having to re-release their packages with a <4.0.0 upper-bound as the only update. It's optimistic, but someone setting their min-SDK to 2.12 or later is definitely aware of null safety, and considered likely to have migrated.

Eventually the code should be released with a <4.0.0 bound, but that's unlikely to happen much before Dart 3.0.0 is released. Without the optimistic resolution, it would be nigh impossible to test code during the 3.0.0 development.

[annagrin]

Thanks @lrhn and @parlough for clarifying! My only problem with this is that it took me some time to understand what is happening with my tests - one was working and another didn't compile, and of course the main difference was the SDK constraint. I think it would be easier if the SDK constraint just failed to resolve in both cases and I had to update it.

I am not sure how common this situation would be for other people, as I am compiling weak null safety code using build runner to test that it is still working with current dwds.

[mit-mit]

@annagrin would the error message from #3686 have helped you to understand why sdk: ">=2.10.0 <3.0.0" failed?

[mit-mit]

@annagrin can you take a look at #3686, please?

[mit-mit]

With that fix patched into my SDK, the output for the app at the top is:

$ ~/dev/dartsdk/sdk/xcodebuild/ReleaseARM64/dart-sdk/bin/dart pub get
Resolving dependencies...
The current Dart SDK version is 3.0.0-edge.181c9962b13b888ea8164e470be8dd48845014d1.

Because testapp4 requires SDK version >=2.10.0 <3.0.0, version solving failed.

The lower bound of ">=2.10.0 <3.0.0" does not enable null safety.

[sigurdm]

Is the fix sufficient?

[mit-mit]

It looks like @annagrin might be out of office. I think it's sufficient, but let's wait and get confirmation?

[mit-mit]

#3723 suggests one further refinement to the output, that would change the text to:

$ ~/dev/pub/bin/pub.exe get
Resolving dependencies...
The current Dart SDK version is 3.0.0-76.0.dev.

Because oldapp doesn't support null safety, version solving failed.

The lower bound of ">=2.9.0 <3.0.0" must be 2.12.0 or higher for null safety.

[annagrin]

@mit-mit apologies for the delay, I am back to office now.

The lower bound of ">=2.9.0 <3.0.0" must be 2.12.0 or higher for null safety.

This would help, thanks! Will there be a message above that it is the SDK constraint that needed to be updated?

[mit-mit]

Thanks @annagrin, I'll change the output to "The lower bound of "sdk: >=2.9.0 <3.0.0" must be 2.12.0 or higher for null safety."