Remove splice internal representation from public API #6073
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nicolasstucki
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odersky
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Mar 17, 2019
| @@ -203,7 +203,7 @@ object StagedTuple { | |||
| if (!specialize) '{dynamic_++[Self, That]($self, $that)} | |||
| else { | |||
| def genericConcat(xs: Expr[Tuple], ys: Expr[Tuple]): Expr[Tuple] = | |||
| fromArrayStaged[Tuple]('{${ toArrayStaged(xs, None) } ++ ${ toArrayStaged(ys, None) }}, None) | |||
| fromArrayStaged[Tuple]('{${ toArrayStaged(xs, None) } ++ (${ toArrayStaged(ys, None) }: Array[Object])}, None) | |||
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Why is the ascription needed here?
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From the desugaring of ${...} to def exprSplice[T](x: Expr[T]): T we get now need to infer T as well as the types of ++.
The acctual error is
[error] 206 | fromArrayStaged[Tuple]('{${ toArrayStaged(xs, None) } ++ ${ toArrayStaged(ys, None) }}, None)
[error] | ^^^^^^^^^^^^^^^^^^^^^^^
[error] | Found: quoted.Expr[Array[Object]]
[error] | Required: quoted.Expr[scala.collection.GenTraversableOnce[Object]]There was a problem hiding this comment.
That's problematic. We should avoid type ascriptions that need to be added for obscure reasons. Should we change the desugaring instead?
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Actually, this is an instance of #6126 which is quite specific to ++ with Arrays. If fixed this would not be an issue.
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I'll have a look at #6126.
`scala.internal.Quoted.exprSplice` can be used for the same purpose by explicily setting the type parameter of `exprSplice` to a phase correct type alias.
Currently type inference for `Expr` of union types is not precise enough as reported in scala#4867. This implies that currently we cannot have macros of the form ```scala inline def foo(x: T) <: X | Y = ${ ... } ``` but we can always default back to the less informative alternative ```scala inline def foo(x: T) <: Any = ${ ... } ``` Both form will refine the type to the type of the expression returned by the macro.
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This removes the
$splicepublic member fromExprthat was only for compiler internal representation.sealed abstract class Expr[+T] { - final def `$splice`: T = throw new Error("splice should have been compiled away") ... }And remove the
asInstanceOfs added around each splice to make pickling/unpickling retain phase consistency on types.With this change, we also start hitting an instance of #4867 that disallow us to write splices of expressions of union types. If #4867 is fixed we would not have this issue.