[backport] desugar switchable matches with guards in async methods #10779
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Backport of #10775
The async transformation supports
Match
trees that are left in place for the backend to emit a switch in bytecode.Guards are desugared into a jump to the default case
becomes
This pattern is unexpected for the async transform and leads to invalid bytecode if the guard
p
has an await call.The fix is to desugar switchable matches with guards in patmat if the enclosing method has the
AsyncAttachment
.