[CP] Fix for issue #59901

[osa1]

Commit(s) to merge

• 78ce85a
• https://dart-review.googlesource.com/c/sdk/+/404562

Target

beta

Prepared changelist for beta/stable

(Is this necessary? https://github.com/dart-lang/sdk/blob/main/docs/Cherry-picks-to-a-release-channel.md says changelog is only necessary for CPs into stable)

Issue Description

In code like if (x == <string constant>) { ... use x ... } TFA normally propagates the information that x equals to the string constant when processing the body of the conditional.

However unlike in VM, in dart2wasm, x being equal to a string constant or literal does not mean x and the literal or constant have the same class.

Assuming this causes miscompilation, which manifests itself as a runtime crash.

What is the fix

Don't assume that, in dart2wasm, a variable being equal to a string means the variable and string have the same class.

Why cherry-pick

Blocks user migrating from dart:html to package:web.

Risk

None

Issue link(s)

#59901

[dart-github-bot]

Summary: Dart2wasm incorrectly assumed string variable and literal equality implied same class, causing miscompilation and crashes. The fix prevents this assumption in dart2wasm.

[mit-mit]

SGTM

[gmpassos]

Thanks for cherry-picking this. I was about to open a CP issue, but then I saw this.

Please, release a Dart 3.6.2 if possible.