[CP] Fix nullability of bad cast to FunctionType in pkg/kernel/lib/clone.dart

[fishythefish]

Commit(s) to merge

ea84221

Target

stable

Prepared changelist for beta/stable

https://dart-review.googlesource.com/c/sdk/+/307964

Issue Description

There is a visitor in the CFE whose job it is to clone AST nodes. InstanceGetterInvocation nodes have a functionType, but this field is optional. The visitor for this node type had visitOptionalType(node.functionType) as FunctionType instead of as FunctionType?, so it would crash whenever there was no functionType.

This likely affects all platforms. (Edit: This might only be the Flutter web workflow - see Siggi's comment below and the linked issue for details.)

What is the fix

Change the cast from as FunctionType to as FunctionType?

Why cherry-pick

It's a low-risk fix that addresses an obvious bug in the CFE that users cannot work around easily. The code still statically typechecks and any successful cast to FunctionType will still be a successful cast to FunctionType?.

It fixes the issues users are running into in #52403. (Note the last few comments - users are looking for this to be addressed quickly.)

Risk

low

Issue link(s)

#52403

Extra Info

No response

[sigmundch]

cc @johnniwinther since the fix is in the CFE.

I'm very much in favor of cherry-picking. The change is extremely small and low risk, and mitigates crashes multiple customers have noticed in the Flutter 3.10 release.

Even though the change is in the CFE, I've only seen this issue because of the serialization step used in the flutter tool for flutter-web. So, I'm not sure if this crash is visible in other workflows.

[johnniwinther]

LGTM