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Fix #10951: update typedDynamicSelect #10952

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Merged
merged 3 commits into from
Jan 3, 2021
Merged

Fix #10951: update typedDynamicSelect #10952

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26c8564
selectDynamic type parameters fix
albertpchen Dec 30, 2020
04ea25c
add PreTypedTypeTree to memoize type checked trees
albertpchen Dec 31, 2020
13624d5
revert MemoizedTypeTree, use TypedSplice instead
albertpchen Jan 2, 2021
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6 changes: 6 additions & 0 deletions compiler/src/dotty/tools/dotc/ast/untpd.scala
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Expand Up @@ -345,6 +345,12 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
def derivedTree(originalSym: Symbol)(using Context): tpd.Tree
}

/** A type tree that memoizes the result of a typed tree. Used when
* typechecking selectDynamic calls to prevent typechecking type arguments
* multiple types.
*/
final class MemoizedTypeTree(val result: tpd.Tree)(implicit @constructorOnly src: SourceFile) extends TypeTree

/** Property key containing TypeTrees whose type is computed
* from the symbol in this type. These type trees have marker trees
* TypeRefOfSym or InfoOfSym as their originals.
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Applications.scala
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Expand Up @@ -1076,7 +1076,7 @@ trait Applications extends Compatibility {
case _ =>
}
def tryDynamicTypeApply(): Tree = typedFn match {
case typedFn: Select if !pt.isInstanceOf[FunProto] => typedDynamicSelect(typedFn, typedArgs, pt)
case typedFn: Select if !pt.isInstanceOf[FunProto] => typedDynamicSelect(typedFn, typedArgs.map(untpd.MemoizedTypeTree(_)), pt)
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Let's see whether we find a way to avoid MemoizedTypeTree. Why did it not work with typedArgs in the first place? What issue gets fixed by wrapping the arguments in MemoizedTypeTree?

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the issue with typedArgs was that after
tree.args: List(Tuple(List(Ident(Int), Ident(Int))))

gets typed to
typedArgs: List(AppliedTypeTree(TypeTree[TypeRef(...,class Tuple2)],List(Ident(Int), Ident(Int))))

it fails when it tries to type check the AppliedTypeTree again because typedAppliedTypeTree sets pt to AnyTypeConstructorProto
https://github.com/lampepfl/dotty/blob/04ea25cfe9c77f612964ba306f070ba058ee695c/compiler/src/dotty/tools/dotc/typer/Typer.scala#L1700-L1703

So I wrapped typedArgs with MemoizedTypeTree so that typedTypeTree could know that the args were already type checked and return the cached results instead of an error type. doing a hasType check + cast worked as well, but having an explicit memoize type tree seemed like a safer solution.

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Thanks for explaining! We actually already have an analogous memoization mechanism in place. It's untpd.TypedSplice. Can you try to simply replace MemoizedTypeTree with untpd.TypedSplice?

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thanks for the suggestion! i've updated the PR

case _ => tree.withType(TryDynamicCallType)
}
if (typedFn.tpe eq TryDynamicCallType) tryDynamicTypeApply()
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Dynamic.scala
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Expand Up @@ -106,7 +106,7 @@ trait Dynamic {
* Note: inner part of translation foo.bar(baz) = quux ~~> foo.selectDynamic(bar).update(baz, quux) is achieved
* through an existing transformation of in typedAssign [foo.bar(baz) = quux ~~> foo.bar.update(baz, quux)].
*/
def typedDynamicSelect(tree: untpd.Select, targs: List[Tree], pt: Type)(using Context): Tree =
def typedDynamicSelect(tree: untpd.Select, targs: List[untpd.Tree], pt: Type)(using Context): Tree =
typedApply(coreDynamic(tree.qualifier, nme.selectDynamic, tree.name, tree.span, targs), pt)

/** Translate selection that does not typecheck according to the normal rules into a updateDynamic.
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1 change: 1 addition & 0 deletions compiler/src/dotty/tools/dotc/typer/Typer.scala
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Expand Up @@ -1695,6 +1695,7 @@ class Typer extends Namer
case None =>
errorTree(tree, "Something's wrong: missing original symbol for type tree")
}
case tree: untpd.MemoizedTypeTree => tree.result
case _ =>
tree.withType(
if (isFullyDefined(pt, ForceDegree.flipBottom)) pt
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8 changes: 8 additions & 0 deletions tests/pos/i10951.scala
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@@ -0,0 +1,8 @@
import scala.language.dynamics

object Dyn extends Dynamic:
def selectDynamic[T](name: String): Option[T] = None

val a: Option[(Int, Int)] = Dyn.asdf[Tuple2[Int, Int]]
val b: Option[(Int, Int)] = Dyn.selectDynamic[(Int, Int)]("asdf")
val c: Option[(Int, Int)] = Dyn.asdf[(Int, Int)]