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Refine criterion when we can skip an asSeenFrom #10982

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Merged
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Jan 6, 2021
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Refine criterion when we can skip an asSeenFrom #10982

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11 changes: 10 additions & 1 deletion compiler/src/dotty/tools/dotc/core/Denotations.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1063,7 +1063,16 @@ object Denotations {
info.asSeenFrom(pre, owner),
if (symbol.is(Opaque) || this.prefix != NoPrefix) pre else this.prefix)

if (!owner.membersNeedAsSeenFrom(pre) || symbol.is(NonMember)) this
// Tt could happen that we see the symbol with prefix `this` as a member a different class
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Suggested change
// Tt could happen that we see the symbol with prefix `this` as a member a different class
// It could happen that we see the symbol with prefix `this` as a member of a different class

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We have similar logic in Types.scala:

    private def infoDependsOnPrefix(symd: SymDenotation, prefix: Type)(using Context): Boolean =
      symd.maybeOwner.membersNeedAsSeenFrom(prefix) && !symd.is(NonMember)

I'm wondering if it is worth creating a method to abstract the logic?

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Interesting observation! This looked promising at first, but in the end I found no way to improve over the status quo. The problem is that the code in Types only works for SymDenotations, whereas the more complicated logic in Denotations works also for SingleDenotations and it's difficult to break it out.

// through a self type and that it then has a different info. In this case we have to go
// through the asSeenFrom to switch the type back. Test case is pos/i9352.scala.
def hasOriginalInfo: Boolean = this match
case sd: SymDenotation => true
case _ => info eq symbol.info

if !owner.membersNeedAsSeenFrom(pre) && ((pre ne owner.thisType) || hasOriginalInfo)
|| symbol.is(NonMember)
then this
else derived(symbol.info)
}
}
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8 changes: 8 additions & 0 deletions tests/pos/i9352.scala
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@@ -0,0 +1,8 @@
abstract class Foo[B] extends Bar[B]

trait Bar[A]:
self: Foo[A] =>

def foo : Unit = bar(???)
def bar(f: A) : Unit