This is basically a workaround for a slightly different IR generated by
fir2ir vs psi2ir. Simplified, psi2ir generates something like this for
the sample from KT-59218:
TRY type=Unit
try: BLOCK type=Unit
VAR methodHandle [...]
TYPE_OP type=Unit origin=IMPLICIT_COERCION_TO_UNIT
CALL invokeExact [...]
While fir2ir generates the following:
TYPE_OP type=Unit origin=IMPLICIT_COERCION_TO_UNIT
TRY type=Any?
try: BLOCK type=Any?
VAR methodHandle [...]
CALL invokeExact [...]
The lowering relies on the fact that a polymorphic call (`invokeExact`
in this case) is a direct argument to the TYPE_OP, to determine the
correct return type (Unit in this case) to be generated in the bytecode.
The solution here is to push the type coercion "through" all the
block-like structures (`try`, `when`, container expression) so that if
the last statement in the block is a polymorphic call, it gets properly
converted even if the whole block is under a type coercion operation, as
it happens in fir2ir. We achieve that by using the "data" parameter of
the IR transformer: appropriate immediate children of
IrTypeOperatorCall/IrTry/IrWhen/IrContainerExpression get the type that
the expression needs to be coerced to, and all the other expressions
ignore that type and set it to null when transforming their children.
A proper solution would be to ensure fir2ir generates exactly the same
IR as psi2ir (KT-59781), but since PolymorphicSignatureLowering is the
only lowering affected so far, and polymorphic calls occur very rarely,
it seems safe to workaround it in the lowering for now.
#KT-59218 Fixed
Alexander Udalov
1cb1420e43