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Do not use provablyEmpty anymore; use S <: T + provablyDisjoint(S, T)…
… instead. Fundamentally, the `provablyEmpty(scrut)` test was meant to prevent situations where both `scrut <: pattern` and `provablyDisjoint(scrut, pattern)` are true. That is a problem because it allows a match type to reduce in two different ways depending on the context. Instead, we basically use that combination of `scrut <: pattern` and `provablydisjoint(scrut, pattern)` as the *definition* for `provablyEmpty`. When both those conditions arise together, we refuse to reduce the match type. This allows one example to pass that did not pass before, but that particular example does not seem to cause unsoundness. In a sense, `provablyEmpty` was too strong here.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,116 @@ | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:26:50 -------------------------------------------------------------- | ||
| 26 | def foo[T <: Cov[Int]](c: Child[T]): Trait2 = c.thing // error | ||
| | ^^^^^^^ | ||
| | Found: UpperBoundParametricVariant.M[T] | ||
| | Required: Base.Trait2 | ||
| | | ||
| | where: T is a type in method foo with bounds <: UpperBoundParametricVariant.Cov[Int] | ||
| | | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce UpperBoundParametricVariant.M[T] | ||
| | failed since selector T | ||
| | does not uniquely determine parameter x in | ||
| | case UpperBoundParametricVariant.Cov[x] => Base.N[x] | ||
| | The computed bounds for the parameter are: | ||
| | x <: Int | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:29:29 -------------------------------------------------------------- | ||
| 29 | def thing = new Trait1 {} // error | ||
| | ^ | ||
| | Found: Object with Base.Trait1 {...} | ||
| | Required: Base.N[String & Int] | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce Base.N[String & Int] | ||
| | failed since selector String & Int | ||
| | is uninhabited (there are no values of that type). | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:47:32 -------------------------------------------------------------- | ||
| 47 | def foo(c: Child): Trait2 = c.thing // error | ||
| | ^^^^^^^ | ||
| | Found: InheritanceVariant.M[c.B] | ||
| | Required: Base.Trait2 | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce InheritanceVariant.M[c.B] | ||
| | failed since selector c.B | ||
| | does not uniquely determine parameter a in | ||
| | case InheritanceVariant.Trick[a] => Base.N[a] | ||
| | The computed bounds for the parameter are: | ||
| | a >: Int | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:51:29 -------------------------------------------------------------- | ||
| 51 | def thing = new Trait1 {} // error | ||
| | ^ | ||
| | Found: Object with Base.Trait1 {...} | ||
| | Required: Base.N[String & Int] | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce Base.N[String & Int] | ||
| | failed since selector String & Int | ||
| | is uninhabited (there are no values of that type). | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:69:29 -------------------------------------------------------------- | ||
| 69 | def thing = new Trait1 {} // error | ||
| | ^ | ||
| | Found: Object with Base.Trait1 {...} | ||
| | Required: Base.N[String & Int] | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce Base.N[String & Int] | ||
| | failed since selector String & Int | ||
| | is uninhabited (there are no values of that type). | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:86:29 -------------------------------------------------------------- | ||
| 86 | def thing = new Trait1 {} // error | ||
| | ^ | ||
| | Found: Object with Base.Trait1 {...} | ||
| | Required: Base.N[String & Int] | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce Base.N[String & Int] | ||
| | failed since selector String & Int | ||
| | is uninhabited (there are no values of that type). | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:103:32 ------------------------------------------------------------- | ||
| 103 | def foo(c: Child): Trait2 = c.thing // error | ||
| | ^^^^^^^ | ||
| | Found: UpperBoundVariant.M[c.A] | ||
| | Required: Base.Trait2 | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce UpperBoundVariant.M[c.A] | ||
| | failed since selector c.A | ||
| | does not uniquely determine parameter t in | ||
| | case UpperBoundVariant.Cov[t] => Base.N[t] | ||
| | The computed bounds for the parameter are: | ||
| | t <: Int | ||
| | | ||
| | longer explanation available when compiling with `-explain` | ||
| -- [E007] Type Mismatch Error: tests/neg/6570.scala:107:29 ------------------------------------------------------------- | ||
| 107 | def thing = new Trait1 {} // error | ||
| | ^ | ||
| | Found: Object with Base.Trait1 {...} | ||
| | Required: Base.N[String & Int] | ||
| | | ||
| | Note: a match type could not be fully reduced: | ||
| | | ||
| | trying to reduce Base.N[String & Int] | ||
| | failed since selector String & Int | ||
| | is uninhabited (there are no values of that type). | ||
| | | ||
| | longer explanation available when compiling with `-explain` |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,19 @@ | ||
| object Test { | ||
| type FieldType2[K, +V] = V with KeyTag2[K, V] | ||
| trait KeyTag2[K, +V] extends Any | ||
|
|
||
| type WrapUpper = Tuple | ||
| type Wrap[A] = Tuple1[A] | ||
|
|
||
| type Extract[A <: WrapUpper] = A match { | ||
| case Wrap[h] => h | ||
| } | ||
|
|
||
| summon[Extract[Wrap[FieldType2["foo", Int]]] =:= FieldType2["foo", Int]] | ||
|
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||
| // This used to cause an error because `Tuple1[FieldType2["foo", Int]]` was | ||
| // "provablyEmpty". Since we switched to testing the combination of | ||
| // `scrut <: pattern` *and* `provablyDisjoint(scrut, pattern)` instead, this | ||
| // particular example compiles, because `FieldType2["foo", Int]` is not | ||
| // `provablyDisjoint` from `h` (`Any`). | ||
| } |