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fix: make vals created in desugaring of n-ary lambdas non-synthetic #23896

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fix: make vals created in desugaring of n-ary lambdas non-synthetic #23896

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1 change: 0 additions & 1 deletion compiler/src/dotty/tools/dotc/ast/Desugar.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1964,7 +1964,6 @@ object desugar {
ValDef(param.name, param.tpt, selector(idx))
.withSpan(param.span)
.withAttachment(UntupledParam, ())
.withFlags(Synthetic)
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@jchyb could this cause any issue for coverage? I think we were discussing that with @kasiaMarek

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@jchyb jchyb Sep 12, 2025 •
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I don't think it will make any difference. We recently removed filtering out Synthetic calls for methods (they caused issues for case classes, where most used methods are synthetic), but I don't think anything like that has existed for vals (I suspect we will just get more coverage tags than necessary, but we don't necessarily need the Synthetic flag to be there to be able to fix that).

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Thanks!

}
Function(param :: Nil, Block(vdefs, body))
}
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2 changes: 1 addition & 1 deletion presentation-compiler/src/main/dotty/tools/pc/PcConvertToNamedLambdaParameters.scala
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Expand Up @@ -120,7 +120,7 @@ object PcConvertToNamedLambdaParameters:
}

def isWildcardParam(param: tpd.ValDef)(using Context): Boolean =
param.name.toString.startsWith("_$") && param.symbol.is(Flags.Synthetic)
param.name.toString.startsWith("_$")

def findParamReferencePosition(param: tpd.ValDef, lambda: tpd.Tree)(using Context): Option[SourcePosition] =
var pos: Option[SourcePosition] = None
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12 changes: 12 additions & 0 deletions presentation-compiler/test/dotty/tools/pc/tests/hover/HoverTermSuite.scala
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Expand Up @@ -6,6 +6,18 @@ import org.junit.Test

class HoverTermSuite extends BaseHoverSuite:

@Test def `n-ary lamba` =
check(
"""|object testRepor {
| val listOfTuples = List(1 -> 1, 2 -> 2, 3 -> 3)
|
| listOfTuples.map((k@@ey, value) => key + value)
|}
|""".stripMargin,
"""|val key: Int
|""".stripMargin.hover
)

@Test def `map` =
check(
"""object a {
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