Unhide --no-package-symlinks flag

[kevmoo]

Currently this implemented, but hidden.

Related to #727

[nex3]

For background, we're waiting on doing this until we're reasonably confident that it's possible to rewrite all code that worked with packages/ directories to work with package specs instead. Currently this is blocked on:

• .packages: Ability to pass packages config data into Isolate.spawnUri sdk#23951 so that applications can spawn isolates with different package specs than the parent.
• .packages: Provide an Isolate.packageSpecUri getter sdk#24524 so that applications can spawn Dart subprocesses with the same package spec as the parent.
• Support running without a packages/ directory test#327 as a proof-of-concept that an application that uses package roots/isolate spawning heavily can run without symlinks.

[mit-mit]

Yes, to meet the original goals of 1.13 we need to get this exposed so that externals can confidently test if their tools work without a package dir so that we in return can flip the default in 1.14.

[nex3]

This may or may not be done by 1.13. In addition to the two SDK blockers that have yet to be fixed, the issues blocking dart-lang/test#327 were resolved a lot later than expected. It'll probably take a couple weeks to get test running without symlinks even if we don't encounter any additional features we need. Once that's done we can switch on --no-packages-dir on dev, but I'll want a couple weeks before release to get real-world user data and make sure there aren't any lingering issues that I didn't run into myself.

[mit-mit]

@nex3 anything else we need here? How do you suggest we roll this out?

[mit-mit]

We just experimented a bit; the flag is there, it's just not mentioned in help. So I guess there is enough that we can ask those that depend on the symlinks to try running pub with this flag, and then use the .packages file?

[nex3]

I'm not planning to make the flag visible for 1.14. The flag shouldn't be visible, nor should we encourage users to use it, until we're very confident that users can in practice update their existing packages to run without packages/ directories. I plan to convert pub and the test package as a proof-of-concept, but that work won't be done in time for the upcoming release—and if the feedback from that work necessitates changes in the APIs, there certainly won't be time to adjust them.

[kevmoo]

Blocked on dart-lang/sdk#24093 – which is part of dart-lang/sdk#24112

[mit-mit]

dart-lang/sdk#24093 is done, let go ahead and make this change, please.

[nex3]

I'm still waiting on snapshot tests as well.

[zoechi]

should dart-lang/sdk#24288 be updated/closed as well?

[kevmoo]

should dart-lang/sdk#24288 be updated/closed as well?

Nope. We're going to flip the default from opt-out to opt-in (for creating directories).