[breaking change] Discontinue deprecated core library APIs, part I

[natebosch]

The following Dart core library APIs, which are all currently deprecated, are now being fully removed.

This issue tracks APIs to be discontinued prior to Dart 3.0. Issue #49529 tracks further APIs that will be discontinued in Dart 3.0.

Phase one (pre 3.0)

The following APIs are being removed prior to 3.0, as they are no longer functional and thus their removal is expected to have minimal effect.

dart:convert

• DEFAULT_BUFFER_SIZE (use **TBD**):

CL: https://dart-review.googlesource.com/c/sdk/+/247741

dart:mirrors

The following are removed in Dart 2.19; they were experimental / only used internally in Dart2js (#32507):

• MirrorsUsed class
• Comment class

CL : https://dart-review.googlesource.com/c/sdk/+/248003

dart:io

The following are removed in Dart 2.18:

• SCREAMING CASE constants from core IO: Discontinue the deprecated screaming snake case constants from dart:io #34218
• Additional constants related to io's http: Discontinue the deprecated screaming snake case constants from http #49140

CLs: https://dart-review.googlesource.com/c/sdk/+/235701, https://dart-review.googlesource.com/c/sdk/+/246962

dart:developer

The following are removed in Dart 2.19:

• kInvalidParams, kExtensionError, kExtensionErrorMax, and kExtensionErrorMin in ServiceExtensionResponse (use invalidParams, extensionError, extensionErrorMax, and extensionErrorMin)

CL: https://dart-review.googlesource.com/c/sdk/+/251767

The following will be deprecated in Dart 2.19, and then removed in Dart 3.0:

• MAX_USER_TAGS in UserTag

Phase II, Dart 3.0

See list in #49529

[lrhn]

Most of these are intentionally left in for Dart 2 (I think DeferredLibrary was the only one we believed we could remove, we just didn't want to take a chance late in the process).

I would want to remove them in Dart 3.0 (or when they have been deprecate for at least some amount of time, like six months, but Dart 3.0 probably won't happen before that).

[natebosch]

Another thing we should consider deprecating soon and then deleting for Dart 3.0 is dart:web_sql

For a long time the doc has said not to use it - why continue to publish it?

[mit-mit]

Another thing we should consider deprecating soon and then deleting for Dart 3.0 is dart:web_sql

This was removed a little while back.

[jakemac53]

If possible it would be good if we could analyze pub.dev for usages of these apis before removing them, there is a thread on the dart-lang gitter because somebody got broken by a usage of MirrorsUsed in package:mustache. I filed an issue for them to drop the usage, but it would be better if we could do that prior to actually removing the APIs.