commit 90162cc1f616ec22fc6751fba478cda9d59d4e35
author Nate Biggs <natebiggs@google.com> Tue Jul 30 03:13:58 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Jul 30 03:13:58 2024 +0000
tree 94967b1c905a49a7b0578497d23d0d23a82285be
parent 961bc9236e7715655d97e6c832ed83fb34658bda

[ddc] Fixes for DDC async lowering.

--- Super fix ---
When the arguments to a call contain an async gap (an await in this case), the new lowering will save the receiver to a temp variable so it can be accessed on re-entry to the function body. This is skipped for literals as the literal does not need to be stored in a variable, it can simply be used as-is.

However, the DDC JS AST did not treat "this" or "super" as literals so we ended up with invalid JS like "let temp = super; // do await; temp.foo(...);". In this case "let temp = super;" is invalid, "super" cannot be used as a bare expression.

--- Function scope change ---
The original approach of using TemporaryIds for all the hoisted variables had a large flaw in that it didn't account for scopes captured by closures within async code. Hoisted variables were lifted out of their attached scope and so closures captured the single hoisted declaration and all modified the same variable. See async_scope_capture_test.dart for an example of this breaking.

To fix this we need to box any captured variables into a JS object. We then wrap any closures in an IIFE and pass the correct scope objects in as arguments to "capture" them. This is similar to dart2js's approach of boxing variables for closures. The approach is a little less fine-grained though and we simply box every variable. This makes the logic simpler and provides a better debug experience as users will just be able to look at the available "asyncScope" variables and see all the declarations in the original source code.

--- Add async callback ---
After further study, none of the other backends add implicit calls to 'async_helper.asyncStart' or 'async_helper.asyncEnd'. All the tests (with the exception of the hot_restart_timer_test updated below) are all set up to call asyncStart if they need it. As such we can simply remove and calls in the runtime/sdk to 'addAsyncCallback' (which is then calling 'async_helper.asyncStart'). Ditto with their remove/end counterparts.

Change-Id: Iac9a3774cc43fc2270e3bb2e992893358042e604
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/376020
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Mark Zhou <markzipan@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>