Fix beta-reduction with Nothing and null args
#16938
Conversation
Fixes part of scala#15165
|
It fixes this sub-issue #15165 (comment) |
|
Why do we not always just use the parameter types? |
|
Using the argument type propagates call site knowledge into the implementation of the lambda. This can be used in |
| @@ -128,7 +128,10 @@ object BetaReduce: | |||
| ref.symbol | |||
| case _ => | |||
| val flags = Synthetic | (param.symbol.flags & Erased) | |||
| val tpe = if arg.tpe.dealias.isInstanceOf[ConstantType] then arg.tpe.dealias else arg.tpe.widen | |||
| val tpe = | |||
| if arg.tpe.isBottomType then param.tpe.widenTermRefExpr | |||
There was a problem hiding this comment.
I'm not sure why we use widenTermRefExpr here (and not widen for example), just curious.
There was a problem hiding this comment.
To keep the type precise. For example, if we have a singleton String type we do not want to widen it to String. For example ((x: "foo") => x: "foo").apply(???) should become val x: "foo" = ???; x: "foo" and not val x: String = ???; x: "foo". The second one would not type check after beta-reduction.
Use parameter type as binding type when the argument is of type
Nothingornull.Fixes part of #15165