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SI-7782 Derive type skolems at the ground level

Rather than at the current value of `skolemizationLevel`,
which could be influenced by an in-flight existential
subtype computation.

This method is called in `PolyTypeCompleter`, which
could be constructed by the lazy type completer of the
enclosing class. So currently it is closing over a mutable
variable; hence the Heisenbug.

This issue was exposed by the changes in b74c33e,
which was introduced in Scala 2.10.1.
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retronym committed Aug 26, 2013
1 parent 9600d2b commit bce786f070afe383d203c4d809ef69803330b340
@@ -19,6 +19,9 @@ trait ExistentialsAndSkolems {
* can be deskolemized to the original type parameter. (A skolem is a
* representation of a bound variable when viewed inside its scope.)
* !!!Adriaan: this does not work for hk types.
+ *
+ * Skolems will be created at level 0, rather than the current value
+ * of `skolemizationLevel`. (See SI-7782)
*/
def deriveFreshSkolems(tparams: List[Symbol]): List[Symbol] = {
class Deskolemizer extends LazyType {
@@ -30,7 +33,11 @@ trait ExistentialsAndSkolems {
sym setInfo sym.deSkolemize.info.substSym(typeParams, typeSkolems)
}
}
- (new Deskolemizer).typeSkolems
+
+ val saved = skolemizationLevel
+ skolemizationLevel = 0
+ try new Deskolemizer().typeSkolems
+ finally skolemizationLevel = saved
}
def isRawParameter(sym: Symbol) = // is it a type parameter leaked by a raw type?
View
@@ -0,0 +1,25 @@
+package pack
+
+object Test {
+ import O.empty
+ empty // this will trigger completion of `test`
+ // with skolemizationLevel = 1
+}
+
+object O {
+ // order matters (!!!)
+
+ // this order breaks under 2.10.x
+ def empty[E]: C[E] = ???
+ def empty(implicit a: Any): Any = ???
+}
+
+abstract class C[E] {
+ def foo[BB](f: BB)
+ def test[B](f: B): Any = foo(f)
+ // error: no type parameters for method foo: (<param> f: BB)scala.this.Unit exist so that it can be applied to arguments (B&1)
+ // --- because ---
+ // argument expression's type is not compatible with formal parameter type;
+ // found : B&1
+ // required: ?BB
+}
@@ -0,0 +1,25 @@
+package pack
+
+object Test {
+ import O.empty
+ empty // this will trigger completion of `test`
+ // with skolemizationLevel = 1
+}
+
+object O {
+ // order matters (!!!)
+
+ // this order breaks under 2.11.x
+ def empty(implicit a: Any): Any = ???
+ def empty[E]: C[E] = ???
+}
+
+abstract class C[E] {
+ def foo[BB](f: BB)
+ def test[B](f: B): Any = foo(f)
+ // error: no type parameters for method foo: (<param> f: BB)scala.this.Unit exist so that it can be applied to arguments (B&1)
+ // --- because ---
+ // argument expression's type is not compatible with formal parameter type;
+ // found : B&1
+ // required: ?BB
+}

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