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fix: #24765 SAM conversion for extension method from self-based types #25637

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fix: #24765 SAM conversion for extension method from self-based types #25637

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4 changes: 2 additions & 2 deletions compiler/src/dotty/tools/dotc/ast/tpd.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -398,8 +398,8 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
if !overridden.is(Deferred) then fwdMeth.setFlag(Override)
DefDef(fwdMeth, ref(fn).appliedToArgss(_))
}
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Copilot AI Mar 27, 2026

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This code relies on evaluation order: typeMembers are entered via .entered before calling fwdMeth.allOverriddenSymbols in forwarder, otherwise overridden-signature matching can miss type aliases (as in #24765). Please add a short comment (or refactor to make the ordering/side effect explicit) so a future cleanup doesn’t accidentally revert the fix by inlining/reordering the maps.

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}
}
// Important: `typeMembers` must be entered before calling `allOverriddenSymbols` in `forwarder`,
// otherwise overridden-signature matching can miss type aliases (see scala/bug#24765).

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@halotukozak halotukozak Mar 27, 2026

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I am not sure of the convention in this repo. I will commit this suggestion if the human reviewer asks for it

termForwarders.map((name, sym) => forwarder(name, sym)) ++
typeMembers.map((name, info) => TypeDef(newSymbol(cls, name, Synthetic, info).entered))
val typeDefs = typeMembers.map((name, info) => TypeDef(newSymbol(cls, name, Synthetic, info).entered))
termForwarders.map((name, sym) => forwarder(name, sym)) ++ typeDefs
}
}

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12 changes: 12 additions & 0 deletions tests/pos/i24765.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
import language.experimental.modularity

trait A[T]:
extension(t: T) def foo: T

trait B:
type Self
extension(t: Self) def foo: Self

given A[Int] = x => x // ok before

given Int is B = x => x // was: "cannot override an extension method"
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