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Make hashcode of enum items stable #23218

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Make hashcode of enum items stable #23218

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8ea1261
Make hashcode of enum items stable
mbovel May 21, 2025
5c2e39e
Add more enum hashcode tests
mbovel May 22, 2025
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17 changes: 9 additions & 8 deletions compiler/src/dotty/tools/dotc/transform/SyntheticMembers.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
myCaseSymbols = defn.caseClassSynthesized
myCaseModuleSymbols = myCaseSymbols.filter(_ ne defn.Any_equals)
myEnumValueSymbols = List(defn.Product_productPrefix)
myNonJavaEnumValueSymbols = myEnumValueSymbols :+ defn.Any_toString :+ defn.Enum_ordinal
myNonJavaEnumValueSymbols = myEnumValueSymbols :+ defn.Any_toString :+ defn.Enum_ordinal :+ defn.Any_hashCode
}

def valueSymbols(using Context): List[Symbol] = { initSymbols; myValueSymbols }
Expand Down Expand Up @@ -116,6 +116,12 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
def syntheticDefIfMissing(sym: Symbol): List[Tree] =
if (existingDef(sym, clazz).exists) Nil else syntheticDef(sym) :: Nil

def identifierRef: Tree =
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Note: this was just moved from an inner scope. No changes.

if isSimpleEnumValue then // owner is `def $new(_$ordinal: Int, $name: String) = new MyEnum { ... }`
ref(clazz.owner.paramSymss.head.find(_.name == nme.nameDollar).get)
else // assume owner is `val Foo = new MyEnum { def ordinal = 0 }`
Literal(Constant(clazz.owner.name.toString))

def syntheticDef(sym: Symbol): Tree = {
val synthetic = sym.copy(
owner = clazz,
Expand All @@ -135,12 +141,6 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
else
identifierRef

def identifierRef: Tree =
if isSimpleEnumValue then // owner is `def $new(_$ordinal: Int, $name: String) = new MyEnum { ... }`
ref(clazz.owner.paramSymss.head.find(_.name == nme.nameDollar).get)
else // assume owner is `val Foo = new MyEnum { def ordinal = 0 }`
Literal(Constant(clazz.owner.name.toString))

def ordinalRef: Tree =
if isSimpleEnumValue then // owner is `def $new(_$ordinal: Int, $name: String) = new MyEnum { ... }`
ref(clazz.owner.paramSymss.head.find(_.name == nme.ordinalDollar_).get)
Expand Down Expand Up @@ -357,7 +357,8 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
* For case classes with primitive paramters, see [[caseHashCodeBody]].
*/
def chooseHashcode(using Context) =
if (accessors.isEmpty) Literal(Constant(ownName.hashCode))
if (isNonJavaEnumValue) identifierRef.select(nme.hashCode_).appliedToTermArgs(Nil)
else if (accessors.isEmpty) Literal(Constant(ownName.hashCode))
else if (accessors.exists(_.info.finalResultType.classSymbol.isPrimitiveValueClass))
caseHashCodeBody
else
Expand Down
12 changes: 12 additions & 0 deletions tests/run/stable-enum-hashcodes.check
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
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23 changes: 23 additions & 0 deletions tests/run/stable-enum-hashcodes.scala
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@@ -0,0 +1,23 @@
enum Enum:
case A
case B
case C()
case D()
case E(x: Int)

@main def Test =
// Enum values (were not stable from run to run before #23218)
println(Enum.A.hashCode)
println(Enum.A.hashCode)
println(Enum.B.hashCode)
println(Enum.B.hashCode)

// Other enum cases (were already stable from run to run)
println(Enum.C().hashCode)
println(Enum.C().hashCode)
println(Enum.D().hashCode)
println(Enum.D().hashCode)
println(Enum.E(1).hashCode)
println(Enum.E(1).hashCode)
println(Enum.E(2).hashCode)
println(Enum.E(2).hashCode)
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