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Improve type inference of quote pattern splices #8695

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Merged
merged 1 commit into from
Apr 8, 2020
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Improve type inference of quote pattern splices #8695

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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -73,7 +73,7 @@ trait QuotesAndSplices {
case _ =>
}
if (ctx.mode.is(Mode.QuotedPattern))
if (isFullyDefined(pt, ForceDegree.all)) {
if (isFullyDefined(pt, ForceDegree.flipBottom)) {
def spliceOwner(ctx: Context): Symbol =
if (ctx.mode.is(Mode.QuotedPattern)) spliceOwner(ctx.outer) else ctx.owner
val pat = typedPattern(tree.expr, defn.QuotedExprClass.typeRef.appliedTo(pt))(
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15 changes: 15 additions & 0 deletions tests/run-macros/quote-matcher-inference/Macro_1.scala
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@@ -0,0 +1,15 @@
import scala.quoted._


object Macros {

inline def g(inline x: Unit): Unit = ${impl('x)}

private def impl(x: Expr[Any])(using QuoteContext): Expr[Any] = {
x match
case '{ println(f($y)) } => y
}

}

def f[T](x: T): T = x
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@smarter smarter Apr 8, 2020 •
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flipBottom only special-cases Nothing, but the same issue could reoccur with a different bound like >: Null. I'm not sure how the example above works anyway, when you write:

case '{ println(f($y)) } => y

shouldn't this be expanded to:

case '{ println(f[$t]($y)) } => y

And that way, any println(f[...](...)) call will match, no matter the type argument ?

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That is the current workaround, but it seems hard to expand it while typing it. At some point, this should be tried.

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This is just meant as a patch for a relatively common code pattern. I'm working on the side on implementing the whole pattern desugaring/typing logic which might help us with those tricky expansions.

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@deusaquilus deusaquilus Apr 19, 2020 •
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That would be great! I might have situations with odd types.

10 changes: 10 additions & 0 deletions tests/run-macros/quote-matcher-inference/Test_2.scala
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@@ -0,0 +1,10 @@
import Macros._


object Test {

def main(args: Array[String]): Unit = {
g(println(f((5))))
}

}