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Backport "Check OrType in interpolated toString lint" to 3.3 LTS #523

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Backport "Check OrType in interpolated toString lint" to 3.3 LTS #523

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0aff98a
Make check look intentional per review
som-snytt Jul 22, 2025
f94b108
Make check look intentional per review
tgodzik Jul 26, 2025
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16 changes: 14 additions & 2 deletions compiler/src/dotty/tools/dotc/transform/localopt/FormatChecker.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -228,8 +228,20 @@ class TypedFormatChecker(partsElems: List[Tree], parts: List[String], args: List
case _ => true

def lintToString(arg: Type): Unit =
if ctx.settings.Whas.toStringInterpolated && kind == StringXn && !(arg.widen =:= defn.StringType) && !arg.isPrimitiveValueType
then warningAt(CC)("interpolation uses toString")
def checkIsStringify(tp: Type): Boolean = tp.widen match
case OrType(tp1, tp2) =>
checkIsStringify(tp1) || checkIsStringify(tp2)
case tp =>
!(tp =:= defn.StringType)
&& {
tp =:= defn.UnitType
&& { warningAt(CC)("interpolated Unit value"); true }
||
!tp.isPrimitiveValueType
&& { warningAt(CC)("interpolation uses toString"); true }
}
if ctx.settings.Whas.toStringInterpolated && kind == StringXn then
checkIsStringify(arg): Unit

// what arg type if any does the conversion accept
def acceptableVariants: List[Type] =
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17 changes: 14 additions & 3 deletions compiler/src/dotty/tools/dotc/transform/localopt/StringInterpolatorOpt.scala
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Expand Up @@ -109,9 +109,20 @@ class StringInterpolatorOpt extends MiniPhase:
result
end mkConcat
def lintToString(t: Tree): Unit =
val arg: Type = t.tpe
if ctx.settings.Whas.toStringInterpolated && !(arg.widen =:= defn.StringType) && !arg.isPrimitiveValueType
then report.warning("interpolation uses toString", t.srcPos)
def checkIsStringify(tp: Type): Boolean = tp.widen match
case OrType(tp1, tp2) =>
checkIsStringify(tp1) || checkIsStringify(tp2)
case tp =>
!(tp =:= defn.StringType)
&& {
tp =:= defn.UnitType
&& { report.warning("interpolated Unit value", t.srcPos); true }
||
!tp.isPrimitiveValueType
&& { report.warning("interpolation uses toString", t.srcPos); true }
}
if ctx.settings.Whas.toStringInterpolated then
checkIsStringify(t.tpe): Unit
val sym = tree.symbol
// Test names first to avoid loading scala.StringContext if not used, and common names first
val isInterpolatedMethod =
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