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macros: paying the hardcoding piper #6516

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scabug opened this issue Oct 11, 2012 · 6 comments
Closed

macros: paying the hardcoding piper #6516

scabug opened this issue Oct 11, 2012 · 6 comments
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@paulp
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macros
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2.10.1

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@scabug
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scabug commented Oct 11, 2012

I haven't looked at the cause of this, but it feels like it can only be due to hardcoded handling of "Context" and "PrefixType" somewhere.

import scala.language.experimental.macros
import scala.reflect.macros.Context
import scala.collection.TraversableLike

// This one compiles
object Test {
  type Alias[T, CC[_]] = Context { type PrefixType = TraversableLike[T, CC[T]] }
  def f() = macro f_impl
  def f_impl(c: Alias[Int, List])() = ???
}

// This one doesn't
object Test2 {
  type Ctx = scala.reflect.macros.Context
  type Alias[T, CC[_]] = Ctx { type PrefixType = TraversableLike[T, CC[T]] }

  def f() = macro f_impl
  def f_impl(c: Alias[Int, List])() = ???
}

The error is:

./a.scala:15: error: macro implementation has wrong shape:
 required: (c: scala.reflect.macros.Context)(): c.Expr[Any]
 found   : (c: Test2.Alias[Int,List])(): Nothing
type mismatch for parameter c: scala.reflect.macros.Context does not conform to Test2.Ctx{type PrefixType = scala.collection.TraversableLike[Int,List[Int]]}
  def f() = macro f_impl
                  ^
one error found
@scabug
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scabug commented Oct 11, 2012

Imported From: https://issues.scala-lang.org/browse/SI-6516?orig=1
Reporter: @paulp

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scabug commented Oct 11, 2012

@xeno-by said:
Heh I've already fixed a similar bug back then. But a single dealias wasn't enough: https://github.com/scalamacros/kepler/blob/5b9f4bbf61e0e850a8eb918a278dee7b87628251/src/compiler/scala/tools/nsc/typechecker/Macros.scala#L461

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scabug commented Oct 11, 2012

@paulp said:
I think it will be enough to say "tpe =:= MacroContextClass.tpe" rather than == .

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scabug commented Nov 9, 2012

@xeno-by said:
This bug is being fixed

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scabug commented Jan 30, 2013

@paulp said:
scala/scala#2025

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scabug commented Jan 31, 2013

@paulp said:
ccd7abe897a

@scabug scabug closed this as completed Jan 31, 2013
@scabug scabug added the macros label Apr 7, 2017
@scabug scabug added this to the 2.10.1 milestone Apr 7, 2017
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