8000 Eta-expanded tycon's type params need own owner · adriaanm/scala@802a173 · GitHub
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Eta-expanded tycon's type params need own owner
Since scala#6069, it is possible to have type variables compared to the eta expansion of a class type, which is `[CLASSTPARAM] => Class[CLASSTPARAM]`. After separate compilation, the owner of this type constructor param is adjusted to the root class (see the comments and special cases in Pickler.localizedOwner), which makes it show up to certain subsequent as-seen-from maps as a type parameter of an enclosing class. SBT's ExtractAPI phase runs into this problem. Eta expansion of the tycon type ref uses an owner (NoSymbol) that will not become a class after pickling. Fixes scala/bug#10762
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‎src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala

Lines changed: 10 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -96,15 +96,16 @@ abstract class Pickler extends SubComponent {
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private def isRootSym(sym: Symbol) =
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sym.name.toTermName == rootName && sym.owner == rootOwner
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/** Returns usually symbol's owner, but picks classfile root instead
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* for existentially bound variables that have a non-local owner.
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* Question: Should this be done for refinement class symbols as well?
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*
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* Note: tree pickling also finds its way here; e.g. in scala/bug#7501 the pickling
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* of trees in annotation arguments considers the parameter symbol of a method
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* called in such a tree as "local". The condition `sym.isValueParameter` was
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* added to fix that bug, but there may be a better way.
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*/
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/** Usually `sym.owner`, except when `sym` is pickle-local, while `sym.owner` is not.
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*
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* In the latter case, the alternative owner is the pickle root,
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* or a non-class owner of root (so that term-owned parameters remain term-owned).
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*
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* Note: tree pickling also finds its way here; e.g. in scala/bug#7501 the pickling
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* of trees in annotation arguments considers the parameter symbol of a method
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* called in such a tree as "local". The condition `sym.isValueParameter` was
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* added to fix that bug, but there may be a better way.
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*/
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private def localizedOwner(sym: Symbol) =
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if (isLocalToPickle(sym) && !isRootSym(sym) && !isLocalToPickle(sym.owner))
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// don't use a class as the localized owner for type parameters that are not owned by a class: those are not instantiated by asSeenFrom

‎src/reflect/scala/reflect/internal/Types.scala

Lines changed: 18 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -2337,7 +2337,24 @@ trait Types
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// must initialise symbol, see test/files/pos/ticket0137.scala
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val tpars = initializedTypeParams
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if (tpars.isEmpty) this
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else typeFunAnon(tpars, copyTypeRef(this, pre, sym, tpars map (_.tpeHK))) // todo: also beta-reduce?
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else {
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val tparsAtNonClass =
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// if we're eta-expanding a reference to a class, it can remain the owner of the type params
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// TODO: why does cloning tpars break stuff?
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if (sym.isClass) tpars
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else {
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// NOTE: during pickling, localizedOwner will change the owner to a non-class owner of the pickle root;
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// (the pickle root is the current top-level class).
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// The difference in owner between source-compiled vs class-loaded should not trigger recompilation (or breakage in ASF).
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// We can't just re-use the owner of the type params (the class or type constructor that defines the type params),
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// because if the owner is a type that's under consideration for relativizing, ASF thinks it needs to act on them.
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// We want something enclosing that's not a class, but usually `sym.enclosingSuchThat(_.isTerm)` is NoSymbol anyway
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// when using `sym` (the current owner for `tpars`), pos/t10762 will fail
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val nonClassRoot = sym.enclosingSuchThat(_.isTerm)
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cloneSymbolsAtOwner(tpars, nonClassRoot)
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}
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PolyType(tparsAtNonClass, copyTypeRef(this, pre, sym, tparsAtNonClass map (_.typeConstructor)))
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}
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}
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// only need to rebind type aliases, as typeRef already handles abstract types
@@ -3939,14 +3956,6 @@ trait Types
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@deprecated("use genPolyType(...) instead", "2.10.0") // Used in reflection API
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def polyType(params: List[Symbol], tpe: Type): Type = GenPolyType(params, tpe)
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/** A creator for anonymous type functions, where the symbol for the type function still needs to be created.
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*
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* TODO:
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* type params of anonymous type functions, which currently can only arise from normalising type aliases, are owned by the type alias of which they are the eta-expansion
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* higher-order subtyping expects eta-expansion of type constructors that arise from a class; here, the type params are owned by that class, but is that the right thing to do?
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*/
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def typeFunAnon(tps: List[Symbol], body: Type): Type = typeFun(tps, body)
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/** A creator for a type functions, assuming the type parameters tps already have the right owner. */
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def typeFun(tps: List[Symbol], body: Type): Type = PolyType(tps, body)
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‎test/files/pos/t10762/t10762_1.scala

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,12 @@
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import language.higherKinds
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trait Tycon[A]
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trait MatcherFactory1X[TC1[_]]
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trait Matcher[T]{
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class X {
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def be = {
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def inferTycon[TC1[_]](other: MatcherFactory1X[TC1]): MatcherFactory1X[TC1] = ???
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inferTycon(??? : MatcherFactory1X[Tycon])
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}
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}
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}

‎test/files/pos/t10762/t10762_2.scala

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,4 @@
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object Test {
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val m: Matcher[_] = ???
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val tpinfer = (new m.X).be
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}

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