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Only cache base types when gadt state is empty #19562

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Jan 30, 2024
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Only cache base types when gadt state is empty #19562

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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/core/SymDenotations.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -2192,7 +2192,7 @@ object SymDenotations {
Stats.record("basetype cache entries")
if (!baseTp.exists) Stats.record("basetype cache NoTypes")
}
if (!tp.isProvisional && !CapturingType.isUncachable(tp))
if !(tp.isProvisional || CapturingType.isUncachable(tp) || ctx.gadt.isNarrowing) then
btrCache(tp) = baseTp
else
btrCache.remove(tp) // Remove any potential sentinel value
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13 changes: 13 additions & 0 deletions tests/pos/i19521.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@

final abstract class PLet

sealed trait Expr[+P]
case class ELet[+A](name: String, expr: Expr[A]) extends Expr[A | PLet]

def go[P](e: Expr[P]): P = e match
case ELet(_, _) =>
val x: Expr[P] | ELet[P] = ???
val y: Expr[P] = x // conforms iff using gadt constraints
// error before changes: cast from gadt reasoning was not inserted because
// `Expr[P]` was erronously cached as a baseType of `Expr[P] | ELet[P]` (only true with gadt constraints)
???
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