[ Breaking Change Request ] Remove Observatory from the Dart VM

[bkonyi]

The Observatory developer tooling was developed during the early days of the Dart project to allow for developers to debug, dive into CPU and memory performance characteristics, and inspect program structure of Dart programs. This tool was developed and maintained solely by Dart VM engineers without much input from UX designers, making it powerful for Dart SDK developers but difficult to use by the average Dart developer.

With the development of Dart DevTools by a dedicated team, it no longer makes sense to continue work on Observatory with the associated compatibility and maintenance burdens, especially now that Dart DevTools is at near feature parity with Observatory.

Impact:

Pre-Dart 3.0, users wishing to continue using Observatory will need to pass an --enable-observatory flag for Observatory to be served by the VM. For Dart 3.0, this flag will be removed and remaining Observatory users will be required to move to the new Dart DevTools developer tooling.

Dart DevTools is at near feature parity with Observatory and should meet the needs of the vast majority of Dart developers. Any missing functionality in DevTools that's critical to an individual's workflow should be documented in a new issue on the DevTools issue tracker.

Proposal:

• Pre-Dart 3.0: place Observatory behind --enable-observatory, making Observatory disabled by default by still available.
• Dart 3.0: remove the --enable-observatory flag and remove Observatory completely from the SDK.

cc @a-siva @kenzieschmoll @mit-mit

[a-siva]

//cc @zanderso

[zanderso]

The --enable-observatory flag should be made available before it is required. This is so that we can make changes to pass the flag without losing access to the Observatory.

[bkonyi]

The --enable-observatory flag should be made available before it is required. This is so that we can make changes to pass the flag without losing access to the Observatory.

SGTM.

[bkonyi]

CL adding support for --[no-]serve-observatory is up for review. Default behavior currently is to implicitly set --serve-observatory.

[itsjustkevin]

@vsmenon @Hixie @grouma @zanderso it seems like the comments here have been addressed by @bkonyi . How do we feel about this breaking change request?

[zanderso]

I'm not sure the timeline is achievable, but otherwise the plan sgtm. I also added flutter/devtools#4711 to the tracker.

[a-siva]

lgtm with the caveat that the performance of devtools is acceptable to the engineers who currently use observatory

[vsmenon]

lgtm

[itsjustkevin]

@bkonyi do you find you have enough time to implement this?

[bkonyi]

The initial work needed to allow for disabling Observatory by default is already up for review. Once that change lands and flutter_tools has the right plumbing for --serve-observatory, we can go ahead and change the default behavior to not serve Observatory.

[itsjustkevin]

Thanks @bkonyi, only thing left to address here is the comment by @a-siva.

[zanderso]

@bkonyi --serve-observatory needs to be a flag that the Engine can pass to Dart_SetVMFlags. Is that what your change did?