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Normalize match types before computing implicit scopes
We now try to reduce match types before computing their contributions to an implicit scope. This avoids problems where joint and separate compilations gave different results, as in #20071 and #15183. Background: If a match type is reducible to a type R the compiler is free to replace the match type with R. That should not affect the implicit scope computation. Consequently, we have to try to reduce match types before computing their contributions to an implicit scope. #20071 and #15183 are really the same problem. Both used to compile in sequence and both gave an implicit not found error when two files were compiled together. In #15183 a weird match type was constructed intentionally, in order to avoid an otherwise necessary given import. That exploited a bug in the compiler which this PR fixes.
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+128
-10
lines changed

9 files changed

+128
-10
lines changed

‎compiler/src/dotty/tools/dotc/typer/Implicits.scala

+4-5
Original file line numberDiff line numberDiff line change
@@ -615,9 +615,9 @@ trait ImplicitRunInfo:
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if migrateTo3 then false else sym.is(Package) || sym.isPackageObject
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/** Is `sym` an anchor type for which givens may exist? Anchor types are classes,
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* opaque type aliases, match aliases and abstract types, but not type parameters
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* or package objects.
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*/
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* abstract types, opaque type aliases, and unreducible match aliases, but not type parameters
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* or package objects.
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*/
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private def isAnchor(sym: Symbol) =
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sym.isClass && !isExcluded(sym)
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|| sym.isOpaqueAlias
@@ -636,7 +636,7 @@ trait ImplicitRunInfo:
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else if implicitScopeCache.contains(t) then parts += t
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else
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partSeen += t
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t.dealias match
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t.dealias.normalized match
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case t: TypeRef =>
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if isAnchor(t.symbol) then
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parts += t
@@ -663,7 +663,6 @@ trait ImplicitRunInfo:
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traverseChildren(t)
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case t =>
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traverseChildren(t)
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traverse(t.normalized)
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catch case ex: Throwable => handleRecursive("collectParts of", t.show, ex)
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def apply(tp: Type): collection.Set[Type] =

‎compiler/src/dotty/tools/dotc/typer/ImportInfo.scala

-2
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@@ -180,8 +180,6 @@ class ImportInfo(symf: Context ?=> Symbol,
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assert(myUnimported != null)
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myUnimported.uncheckedNN
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private val isLanguageImport: Boolean = untpd.languageImport(qualifier).isDefined
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private var myUnimported: Symbol | Null = uninitialized
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private var featureCache: SimpleIdentityMap[TermName, java.lang.Boolean] = SimpleIdentityMap.empty

‎tests/neg/i15183.check

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@@ -0,0 +1,96 @@
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-- [E172] Type Error: tests/neg/i15183/test_2.scala:2:17 ---------------------------------------------------------------
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2 |enum Env derives Decoder: // error
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| ^
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|No given instance of type Tuple.Map[m.MirroredElemTypes, Decoder] was found for parameter d of given instance derived in object Decoder.
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|I found:
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|
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| Decoder.summonTuple[(Env.Local : Env), ((Env.Sit : Env), (Env.Prod : Env))](
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| Decoder.derived[(Env.Local : Env)](
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| Env.Local.$asInstanceOf[
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| scala.deriving.Mirror.Singleton{
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| type MirroredMonoType = (Env.Local : Env); type MirroredType = (Env.Local : Env);
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| type MirroredLabel = ("Local" : String)
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| }
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| ],
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| /* missing */summon[Tuple.Map[?1.MirroredElemTypes, Decoder]]),
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| ???)
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|
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|But no implicit values were found that match type Tuple.Map[?1.MirroredElemTypes, Decoder]
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|
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|where: ?1 is an unknown value of type scala.deriving.Mirror.Singleton{
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| type MirroredMonoType = (Env.Local : Env); type MirroredType = (Env.Local : Env);
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| type MirroredLabel = ("Local" : String)
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|}
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|.
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|
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|Note: a match type could not be fully reduced:
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|
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| trying to reduce Tuple.Map[m.MirroredElemTypes, Decoder]
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| failed since selector m.MirroredElemTypes
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| does not match case EmptyTuple => EmptyTuple
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| and cannot be shown to be disjoint from it either.
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| Therefore, reduction cannot advance to the remaining case
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|
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| case h *: t => Decoder[h] *: Tuple.Map[t, Decoder]
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-- [E172] Type Error: tests/neg/i15183/test_2.scala:5:18 ---------------------------------------------------------------
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5 |enum Env2 derives Decoder: // error
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| ^
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|No given instance of type Tuple.Map[m.MirroredElemTypes, Decoder] was found for parameter d of given instance derived in object Decoder.
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|I found:
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|
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| Decoder.summonTuple[Env2.Local, (Env2.Sit, Env2.Prod)](
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| Decoder.derived[Env2.Local](
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| Env2.Local.$asInstanceOf[
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| scala.deriving.Mirror.Product{
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| type MirroredMonoType = Env2.Local; type MirroredType = Env2.Local; type MirroredLabel = ("Local" : String);
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| type MirroredElemTypes = EmptyTuple.type; type MirroredElemLabels = EmptyTuple.type
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| }
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| ],
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| /* missing */summon[Tuple.Map[EmptyTuple.type, Decoder]]),
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| ???)
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|
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|But no implicit values were found that match type Tuple.Map[EmptyTuple.type, Decoder].
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|
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|Note: a match type could not be fully reduced:
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|
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| trying to reduce Tuple.Map[m.MirroredElemTypes, Decoder]
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| failed since selector m.MirroredElemTypes
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| does not match case EmptyTuple => EmptyTuple
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| and cannot be shown to be disjoint from it either.
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| Therefore, reduction cannot advance to the remaining case
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|
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| case h *: t => Decoder[h] *: Tuple.Map[t, Decoder]
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-- [E172] Type Error: tests/neg/i15183/test_2.scala:10:19 --------------------------------------------------------------
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10 |enum Shape derives Decoder: // error
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| ^
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|No given instance of type Tuple.Map[m.MirroredElemTypes, Decoder] was found for parameter d of given instance derived in object Decoder.
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|I found:
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|
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| Decoder.summonTuple[Shape.Rectangle, Shape.Circle *: EmptyTuple.type](
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| Decoder.derived[Shape.Rectangle](
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| Shape.Rectangle.$asInstanceOf[
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| scala.deriving.Mirror.Product{
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| type MirroredMonoType = Shape.Rectangle; type MirroredType = Shape.Rectangle;
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| type MirroredLabel = ("Rectangle" : String); type MirroredElemTypes = (Double, Double);
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| type MirroredElemLabels = (("width" : String), ("height" : String))
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| }
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| ],
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| Decoder.summonTuple[Double, Double *: EmptyTuple.type](Decoder.given_Decoder_Double,
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| Decoder.summonTuple[Double, EmptyTuple.type](Decoder.given_Decoder_Double,
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| /* missing */summon[Tuple.Map[EmptyTuple.type, Decoder]])
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| )
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| ),
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| ???)
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|
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|But no implicit values were found that match type Tuple.Map[EmptyTuple.type, Decoder].
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|
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|Note: a match type could not be fully reduced:
89+
|
90+
| trying to reduce Tuple.Map[m.MirroredElemTypes, Decoder]
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| failed since selector m.MirroredElemTypes
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| does not match case EmptyTuple => EmptyTuple
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| and cannot be shown to be disjoint from it either.
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| Therefore, reduction cannot advance to the remaining case
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|
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| case h *: t => Decoder[h] *: Tuple.Map[t, Decoder]

‎tests/pos/i15183/decoder_1.scala renamed to ‎tests/neg/i15183/decoder_1.scala

File renamed without changes.

‎tests/pos/i15183/test_2.scala renamed to ‎tests/neg/i15183/test_2.scala

+3-3
Original file line numberDiff line numberDiff line change
@@ -1,12 +1,12 @@
11
// Fails in each cases below
2-
enum Env derives Decoder:
2+
enum Env derives Decoder: // error
33
case Local,Sit,Prod
44

5-
enum Env2 derives Decoder:
5+
enum Env2 derives Decoder: // error
66
case Local()
77
case Sit()
88
case Prod()
99

10-
enum Shape derives Decoder:
10+
enum Shape derives Decoder: // error
1111
case Rectangle(width: Double, height: Double)
1212
case Circle(radius: Double)

‎tests/neg/i20071.check

+5
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@@ -0,0 +1,5 @@
1+
2+
-- [E172] Type Error: tests/neg/i20071/test_2.scala:3:20 ---------------------------------------------------------------
3+
3 |def test: Unit = bar // error
4+
| ^
5+
| No given instance of type M[Decoder] was found for parameter d of method bar

‎tests/neg/i20071/decoder_1.scala

+9
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,9 @@
1+
// decoder_1.scala
2+
trait Decoder
3+
object Decoder:
4+
given foo: Int = ???
5+
6+
def bar(using d: M[Decoder]): Any = ???
7+
8+
type M[Y] = Y match
9+
case Decoder => Int

‎tests/neg/i20071/test_2.scala

+3
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@@ -0,0 +1,3 @@
1+
// test_2.scala
2+
// should fail, does when compiling at the same time as decoder_2.scala
3+
def test: Unit = bar // error

‎tests/pos/i20071.scala

+8
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
trait Decoder
2+
object Decoder:
3+
given foo: Int = ???
4+
5+
type DecoderToInt[Why] >: Int <: Int
6+
7+
def bar[T](using d: DecoderToInt[T]): Any = ???
8+
def test: Unit = bar[Decoder]

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