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Backport "Lazy val def member is pattern var" to 3.3 LTS #312

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Merged
merged 2 commits into from
Apr 25, 2025
Merged

Backport "Lazy val def member is pattern var" to 3.3 LTS #312

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9ea521a
Lazy val def member is pattern var
som-snytt Mar 8, 2025
09fb930
Lazy val def member is pattern var
tgodzik Apr 25, 2025
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4 changes: 3 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 @@ -14,11 +14,11 @@ import config.Feature.{sourceVersion, migrateTo3, enabled}
import config.SourceVersion.*
import collection.mutable.ListBuffer
import reporting.*
import annotation.constructorOnly
import printing.Formatting.hl
import config.Printers

import scala.annotation.internal.sharable
import scala.annotation.{unchecked as _, *}
import dotty.tools.dotc.util.SrcPos

object desugar {
Expand Down Expand Up @@ -1255,6 +1255,7 @@ object desugar {
DefDef(named.name.asTermName, Nil, tpt, selector(n))
.withMods(mods &~ Lazy)
.withSpan(named.span)
.withAttachment(PatternVar, ())
else
valDef(
ValDef(named.name.asTermName, tpt, selector(n))
Expand Down Expand Up @@ -1557,6 +1558,7 @@ object desugar {
mayNeedSetter
}

@unused
private def derivedDefDef(original: Tree, named: NameTree, tpt: Tree, rhs: Tree, mods: Modifiers)(implicit src: SourceFile) =
DefDef(named.name.asTermName, Nil, tpt, rhs)
.withMods(mods)
Expand Down
8 changes: 4 additions & 4 deletions compiler/src/dotty/tools/dotc/transform/CheckUnused.scala
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Expand Up @@ -455,11 +455,11 @@ object CheckUnused:
case tree: Bind =>
if !tree.name.isInstanceOf[DerivedName] && !tree.name.is(WildcardParamName) && !tree.hasAttachment(NoWarn) then
pats.addOne((tree.symbol, tree.namePos))
case tree: ValDef if tree.hasAttachment(PatternVar) =>
if !tree.name.isInstanceOf[DerivedName] then
pats.addOne((tree.symbol, tree.namePos))
case tree: NamedDefTree =>
if (tree.symbol ne NoSymbol)
if tree.hasAttachment(PatternVar) then
if !tree.name.isInstanceOf[DerivedName] then
pats.addOne((tree.symbol, tree.namePos))
else if (tree.symbol ne NoSymbol)
&& !tree.name.isWildcard
&& !tree.hasAttachment(NoWarn)
&& !tree.symbol.is(ModuleVal) // track only the ModuleClass using the object symbol, with correct namePos
Expand Down
6 changes: 6 additions & 0 deletions tests/warn/i15503d.scala
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Expand Up @@ -115,3 +115,9 @@ object `mutable patvar in for`:
class `unset var requires -Wunused`:
private var i = 0 // no warn as we didn't ask for it
def f = println(i)

class `i22743 lazy vals are defs`:
def f: (Int, String) = (42, "hello, world")
lazy val (i, s) = f // no warn because def is neither local nor private
val (j, t) = f // existing no warn for val with attachment
private lazy val (k, u) = f // warn // warn a warning so nice, they warn it twice