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Harden GADT constraint handling to survive illegal F-bounds #20325

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Merged
merged 2 commits into from
May 7, 2024
Merged

Harden GADT constraint handling to survive illegal F-bounds #20325

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c544e41
Harden GADT constraint handling to survive illegal F-bounds
odersky May 2, 2024
5e408bd
Add test to best effort blacklist
odersky May 6, 2024
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3 changes: 2 additions & 1 deletion compiler/src/dotty/tools/dotc/core/GadtConstraint.scala
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Expand Up @@ -193,7 +193,8 @@ sealed trait GadtState {
case i => pt.paramRefs(i)
case tp => tp
}

if !param.info.exists then
throw TypeError(em"illegal recursive reference involving $param")
val tb = param.info.bounds
tb.derivedTypeBounds(
lo = substDependentSyms(tb.lo, isUpper = false),
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1 change: 1 addition & 0 deletions compiler/test/dotc/neg-best-effort-pickling.blacklist
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Expand Up @@ -13,6 +13,7 @@ curried-dependent-ift.scala
i17121.scala
illegal-match-types.scala
i13780-1.scala
i20317a.scala

# semantic db generation fails in the first compilation
i1642.scala
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3 changes: 3 additions & 0 deletions tests/neg/i20317.scala
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@@ -0,0 +1,3 @@
type Foo[A] = A

def foo[A <: Foo[A]]: Unit = () // error // error
5 changes: 5 additions & 0 deletions tests/neg/i20317a.scala
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@@ -0,0 +1,5 @@
type SemigroupStructural[A] =
A & { def combine(a: A): A }
def combineAll[A <: SemigroupStructural[A]](
i: A, l: List[A]
): A = l.foldLeft(i)(_.combine(_)) // error
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