[CP] Fix Dart2JS type inference for record accesses on invalid indices.

[biggs0125]

Commit(s) to merge

327a680

Target

stable

Prepared changelist for beta/stable

https://dart-review.googlesource.com/c/sdk/+/304420

Issue Description

#52438

Dart2JS type inference crashes when a record field is accessed but the receiver type does not contain that field.

Users cannot manually generate code like that but code generated by switches can. Specifically when a record is demoted to dynamic/Object and then cased on in a switch with non-matching cases. The generated code from such a switch can contain record accesses that cause these crashes.

What is the fix

The fix is for each record access to check that the type of the receiver supports the selector being used.

Why cherry-pick

This causes crashes in Dart2JS on fairly trivial code. Multiple developers have discovered this bug.

Risk

low

Issue link(s)

#52438

Extra Info

No response

[sigmundch]

I'm very much in support of this cherry-pick - I think this has potential to surface often and the fix is very low risk.

[sigmundch]

(reopening so that the issue is seen by engprod when they create the release candidate, they can close when they confirm it was shipped in 3.0.2)