Analyzer support for ?[

[jensjoha]

Parser support for ?[ was added in cf4e044 (see #40267), but introduced another token that the analyzer currently doesn't save.

I've skipped the following tests in analyzer:

• front_end/parser_testcases/nnbd/issue_40267_case_02.dart
• front_end/parser_testcases/nnbd/issue_40267_case_05.dart

Note: It was reverted. I'll assign this to myself until the fix lands.

[jensjoha]

Change landed again as 3660b9e --- @bwilkerson I took the liberty to assign you. Hope that's okay.

[bwilkerson]

The AST and summary support have landed in https://dart-review.googlesource.com/c/sdk/+/137252. I'm going to hand the issue off to @scheglov for the remainder of the work.

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/138563

[scheglov]

The change landed, but it is not clear to me if we should support both ?.[ and ?[.

[jensjoha]

For what its worth, my understanding is that we should stop supporting ?.[, but that - considering we have tests and whatnot - that should be cleaned up first.