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Mix in the productPrefix hash statically in case class hashCode #22865

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Apr 3, 2025
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Mix in the productPrefix hash statically in case class hashCode #22865

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3 changes: 3 additions & 0 deletions compiler/src/dotty/tools/dotc/core/Definitions.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -505,6 +505,9 @@ class Definitions {
@tu lazy val ScalaRuntime_toArray: Symbol = ScalaRuntimeModule.requiredMethod(nme.toArray)
@tu lazy val ScalaRuntime_toObjectArray: Symbol = ScalaRuntimeModule.requiredMethod(nme.toObjectArray)

@tu lazy val MurmurHash3Module: Symbol = requiredModule("scala.util.hashing.MurmurHash3")
@tu lazy val MurmurHash3_productHash = MurmurHash3Module.info.member(termName("productHash")).suchThat(_.info.firstParamTypes.size == 3).symbol

@tu lazy val BoxesRunTimeModule: Symbol = requiredModule("scala.runtime.BoxesRunTime")
@tu lazy val BoxesRunTimeModule_externalEquals: Symbol = BoxesRunTimeModule.info.decl(nme.equals_).suchThat(toDenot(_).info.firstParamTypes.size == 2).symbol
@tu lazy val ScalaStaticsModule: Symbol = requiredModule("scala.runtime.Statics")
Expand Down
66 changes: 32 additions & 34 deletions compiler/src/dotty/tools/dotc/transform/SyntheticMembers.scala
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Expand Up @@ -15,6 +15,7 @@ import util.Property
import util.Spans.Span
import config.Printers.derive
import NullOpsDecorator.*
import scala.runtime.Statics

object SyntheticMembers {

Expand Down Expand Up @@ -101,6 +102,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
val isSimpleEnumValue = isEnumValue && !clazz.owner.isAllOf(EnumCase)
val isJavaEnumValue = isEnumValue && clazz.derivesFrom(defn.JavaEnumClass)
val isNonJavaEnumValue = isEnumValue && !isJavaEnumValue
val ownName = clazz.name.stripModuleClassSuffix.toString

val symbolsToSynthesize: List[Symbol] =
if clazz.is(Case) then
Expand All @@ -124,8 +126,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
def forwardToRuntime(vrefs: List[Tree]): Tree =
ref(defn.runtimeMethodRef("_" + sym.name.toString)).appliedToTermArgs(This(clazz) :: vrefs)

def ownName: Tree =
Literal(Constant(clazz.name.stripModuleClassSuffix.toString))
def ownNameLit: Tree = Literal(Constant(ownName))

def nameRef: Tree =
if isJavaEnumValue then
Expand All @@ -152,7 +153,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
Literal(Constant(candidate.get))

def toStringBody(vrefss: List[List[Tree]]): Tree =
if (clazz.is(ModuleClass)) ownName
if (clazz.is(ModuleClass)) ownNameLit
else if (isNonJavaEnumValue) identifierRef
else forwardToRuntime(vrefss.head)

Expand All @@ -165,7 +166,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
case nme.ordinal => ordinalRef
case nme.productArity => Literal(Constant(accessors.length))
case nme.productPrefix if isEnumValue => nameRef
case nme.productPrefix => ownName
case nme.productPrefix => ownNameLit
case nme.productElement =>
if ctx.settings.YcompileScala2Library.value then productElementBodyForScala2Compat(accessors.length, vrefss.head.head)
else productElementBody(accessors.length, vrefss.head.head)
Expand Down Expand Up @@ -335,39 +336,36 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
ref(accessors.head).select(nme.hashCode_).ensureApplied
}

/** The class
*
* ```
* case object C
* ```
*
* gets the `hashCode` method:
*
* ```
* def hashCode: Int = "C".hashCode // constant folded
* ```
*
* The class
*
* ```
* case class C(x: T, y: U)
* ```
*
* if none of `T` or `U` are primitive types, gets the `hashCode` method:
*
* ```
* def hashCode: Int = ScalaRunTime._hashCode(this)
* ```
*
* else if either `T` or `U` are primitive, gets the `hashCode` method implemented by [[caseHashCodeBody]]
/**
* A `case object C` or a `case class C()` without parameters gets the `hashCode` method
* ```
* def hashCode: Int = "C".hashCode // constant folded
* ```
*
* Otherwise, if none of the parameters are primitive types:
* ```
* def hashCode: Int = MurmurHash3.productHash(
* this,
* Statics.mix(0xcafebabe, "C".hashCode), // constant folded
* ignorePrefix = true)
* ```
*
* The implementation used to invoke `ScalaRunTime._hashCode`, but that implementation mixes in the result
* of `productPrefix`, which causes scala/bug#13033. By setting `ignorePrefix = true` and mixing in the case
* name into the seed, the bug can be fixed and the generated code works with the unchanged Scala library.
*
* For case classes with primitive paramters, see [[caseHashCodeBody]].
*/
def chooseHashcode(using Context) =
if (clazz.is(ModuleClass))
Literal(Constant(clazz.name.stripModuleClassSuffix.toString.hashCode))
if (accessors.isEmpty) Literal(Constant(ownName.hashCode))
else if (accessors.exists(_.info.finalResultType.classSymbol.isPrimitiveValueClass))
caseHashCodeBody
else
ref(defn.ScalaRuntime__hashCode).appliedTo(This(clazz))
ref(defn.MurmurHash3Module).select(defn.MurmurHash3_productHash).appliedTo(
This(clazz),
Literal(Constant(Statics.mix(0xcafebabe, ownName.hashCode))),
Literal(Constant(true))
)

/** The class
*
Expand All @@ -380,7 +378,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
* ```
* def hashCode: Int = {
* <synthetic> var acc: Int = 0xcafebabe
* acc = Statics.mix(acc, this.productPrefix.hashCode());
* acc = Statics.mix(acc, "C".hashCode);
* acc = Statics.mix(acc, x);
* acc = Statics.mix(acc, Statics.this.anyHash(y));
* Statics.finalizeHash(acc, 2)
Expand All @@ -391,7 +389,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
val acc = newSymbol(ctx.owner, nme.acc, Mutable | Synthetic, defn.IntType, coord = ctx.owner.span)
val accDef = ValDef(acc, Literal(Constant(0xcafebabe)))
val mixPrefix = Assign(ref(acc),
ref(defn.staticsMethod("mix")).appliedTo(ref(acc), This(clazz).select(defn.Product_productPrefix).select(defn.Any_hashCode).appliedToNone))
ref(defn.staticsMethod("mix")).appliedTo(ref(acc), Literal(Constant(ownName.hashCode))))
val mixes = for (accessor <- accessors) yield
Assign(ref(acc), ref(defn.staticsMethod("mix")).appliedTo(ref(acc), hashImpl(accessor)))
val finish = ref(defn.staticsMethod("finalizeHash")).appliedTo(ref(acc), Literal(Constant(accessors.size)))
Expand Down
2 changes: 1 addition & 1 deletion tests/run-macros/tasty-extractors-2.check
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Expand Up @@ -49,7 +49,7 @@ TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
Inlined(None, Nil, Block(List(ClassDef("Foo", DefDef("<init>", List(TermParamClause(Nil)), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), None, List(DefDef("a", Nil, Inferred(), Some(Literal(IntConstant(0))))))), Literal(UnitConstant())))
TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")

Inlined(None, Nil, Block(List(ClassDef("Foo", DefDef("<init>", List(TermParamClause(Nil)), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), TypeSelect(Select(Ident("_root_"), "scala"), "Product"), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), None, List(DefDef("hashCode", List(TermParamClause(Nil)), Inferred(), Some(Apply(Ident("_hashCode"), List(This(Some("Foo")))))), DefDef("equals", List(TermParamClause(List(ValDef("x$0", Inferred(), None)))), Inferred(), Some(Apply(Select(Apply(Select(This(Some("Foo")), "eq"), List(TypeApply(Select(Ident("x$0"), "$asInstanceOf$"), List(Inferred())))), "||"), List(Match(Ident("x$0"), List(CaseDef(Bind("x$0", Typed(Wildcard(), Inferred())), None, Apply(Select(Literal(BooleanConstant(true)), "&&"), List(Apply(Select(Ident("x$0"), "canEqual"), List(This(Some("Foo"))))))), CaseDef(Wildcard(), None, Literal(BooleanConstant(false))))))))), DefDef("toString", List(TermParamClause(Nil)), Inferred(), Some(Apply(Ident("_toString"), List(This(Some("Foo")))))), DefDef("canEqual", List(TermParamClause(List(ValDef("that", Inferred(), None)))), Inferred(), Some(TypeApply(Select(Ident("that"), "isInstanceOf"), List(Inferred())))), DefDef("productArity", Nil, Inferred(), Some(Literal(IntConstant(0)))), DefDef("productPrefix", Nil, Inferred(), Some(Literal(StringConstant("Foo")))), DefDef("productElement", List(TermParamClause(List(ValDef("n", Inferred(), None)))), Inferred(), Some(Match(Ident("n"), List(CaseDef(Wildcard(), None, Apply(Ident("throw"), List(Apply(Select(New(Inferred()), "<init>"), List(Apply(Select(Ident("n"), "toString"), Nil)))))))))), DefDef("productElementName", List(TermParamClause(List(ValDef("n", Inferred(), None)))), Inferred(), Some(Match(Ident("n"), List(CaseDef(Wildcard(), None, Apply(Ident("throw"), List(Apply(Select(New(Inferred()), "<init>"), List(Apply(Select(Ident("n"), "toString"), Nil)))))))))), DefDef("copy", List(TermParamClause(Nil)), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))))), ValDef("Foo", TypeIdent("Foo$"), Some(Apply(Select(New(TypeIdent("Foo$")), "<init>"), Nil))), ClassDef("Foo$", DefDef("<init>", List(TermParamClause(Nil)), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), Inferred()), Some(ValDef("_", Singleton(Ident("Foo")), None)), List(DefDef("apply", List(TermParamClause(Nil)), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))), DefDef("unapply", List(TermParamClause(List(ValDef("x$1", Inferred(), None)))), Singleton(Literal(BooleanConstant(true))), Some(Literal(BooleanConstant(true)))), DefDef("toString", Nil, Inferred(), Some(Literal(StringConstant("Foo")))), TypeDef("MirroredMonoType", TypeBoundsTree(Inferred(), Inferred())), DefDef("fromProduct", List(TermParamClause(List(ValDef("x$0", Inferred(), None)))), Inferred(), Some(Block(Nil, Apply(Select(New(Inferred()), "<init>"), Nil))))))), Literal(UnitConstant())))
Inlined(None, Nil, Block(List(ClassDef("Foo", DefDef("<init>", List(TermParamClause(Nil)), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), TypeSelect(Select(Ident("_root_"), "scala"), "Product"), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), None, List(DefDef("hashCode", List(TermParamClause(Nil)), Inferred(), Some(Literal(IntConstant(70822)))), DefDef("equals", List(TermParamClause(List(ValDef("x$0", Inferred(), None)))), Inferred(), Some(Apply(Select(Apply(Select(This(Some("Foo")), "eq"), List(TypeApply(Select(Ident("x$0"), "$asInstanceOf$"), List(Inferred())))), "||"), List(Match(Ident("x$0"), List(CaseDef(Bind("x$0", Typed(Wildcard(), Inferred())), None, Apply(Select(Literal(BooleanConstant(true)), "&&"), List(Apply(Select(Ident("x$0"), "canEqual"), List(This(Some("Foo"))))))), CaseDef(Wildcard(), None, Literal(BooleanConstant(false))))))))), DefDef("toString", List(TermParamClause(Nil)), Inferred(), Some(Apply(Ident("_toString"), List(This(Some("Foo")))))), DefDef("canEqual", List(TermParamClause(List(ValDef("that", Inferred(), None)))), Inferred(), Some(TypeApply(Select(Ident("that"), "isInstanceOf"), List(Inferred())))), DefDef("productArity", Nil, Inferred(), Some(Literal(IntConstant(0)))), DefDef("productPrefix", Nil, Inferred(), Some(Literal(StringConstant("Foo")))), DefDef("productElement", List(TermParamClause(List(ValDef("n", Inferred(), None)))), Inferred(), Some(Match(Ident("n"), List(CaseDef(Wildcard(), None, Apply(Ident("throw"), List(Apply(Select(New(Inferred()), "<init>"), List(Apply(Select(Ident("n"), "toString"), Nil)))))))))), DefDef("productElementName", List(TermParamClause(List(ValDef("n", Inferred(), None)))), Inferred(), Some(Match(Ident("n"), List(CaseDef(Wildcard(), None, Apply(Ident("throw"), List(Apply(Select(New(Inferred()), "<init>"), List(Apply(Select(Ident("n"), "toString"), Nil)))))))))), DefDef("copy", List(TermParamClause(Nil)), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))))), ValDef("Foo", TypeIdent("Foo$"), Some(Apply(Select(New(TypeIdent("Foo$")), "<init>"), Nil))), ClassDef("Foo$", DefDef("<init>", List(TermParamClause(Nil)), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), Inferred()), Some(ValDef("_", Singleton(Ident("Foo")), None)), List(DefDef("apply", List(TermParamClause(Nil)), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))), DefDef("unapply", List(TermParamClause(List(ValDef("x$1", Inferred(), None)))), Singleton(Literal(BooleanConstant(true))), Some(Literal(BooleanConstant(true)))), DefDef("toString", Nil, Inferred(), Some(Literal(StringConstant("Foo")))), TypeDef("MirroredMonoType", TypeBoundsTree(Inferred(), Inferred())), DefDef("fromProduct", List(TermParamClause(List(ValDef("x$0", Inferred(), None)))), Inferred(), Some(Block(Nil, Apply(Select(New(Inferred()), "<init>"), Nil))))))), Literal(UnitConstant())))
TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")

Inlined(None, Nil, Block(List(ClassDef("Foo1", DefDef("<init>", List(TermParamClause(List(ValDef("a", TypeIdent("Int"), None)))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), None, List(ValDef("a", Inferred(), None)))), Literal(UnitConstant())))
Expand Down
69 changes: 69 additions & 0 deletions tests/run/t13033.scala
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@@ -0,0 +1,69 @@
// This method will be in the 2.13.17 standard library. Until this test declares a copy of it.
// import scala.util.hashing.MurmurHash3.caseClassHash
def caseClassHash(x: Product, caseClassName: String = null): Int =
import scala.runtime.Statics._
val arr = x.productArity
val aye = (if (caseClassName != null) caseClassName else x.productPrefix).hashCode
if (arr == 0) aye
else {
var h = 0xcafebabe
h = mix(h, aye)
var i = 0
while (i < arr) {
h = mix(h, x.productElement(i).##)
i += 1
}
finalizeHash(h, arr)
}


case class C1(a: Int)
class C2(a: Int) extends C1(a) { override def productPrefix = "C2" }
class C3(a: Int) extends C1(a) { override def productPrefix = "C3" }
case class C4(a: Int) { override def productPrefix = "Sea4" }
case class C5()
case object C6
case object C6b { override def productPrefix = "Sea6b" }
case class C7(s: String) // hashCode forwards to ScalaRunTime._hashCode if there are no primitives
class C8(s: String) extends C7(s) { override def productPrefix = "C8" }

case class VCC(x: Int) extends AnyVal

object Test extends App {
val c1 = C1(1)
val c2 = new C2(1)
val c3 = new C3(1)
assert(c1 == c2)
assert(c2 == c1)
assert(c2 == c3)
assert(c1.hashCode == c2.hashCode)
assert(c2.hashCode == c3.hashCode)

assert(c1.hashCode == caseClassHash(c1))
// `caseClassHash` mixes in the `productPrefix.hashCode`, while `hashCode` mixes in the case class name statically
assert(c2.hashCode != caseClassHash(c2))
assert(c2.hashCode == caseClassHash(c2, c1.productPrefix))

val c4 = C4(1)
assert(c4.hashCode != caseClassHash(c4))
assert(c4.hashCode == caseClassHash(c4, "C4"))

assert((1, 2).hashCode == caseClassHash(1 -> 2))
assert(("", "").hashCode == caseClassHash("" -> ""))

assert(C5().hashCode == caseClassHash(C5()))
assert(C6.hashCode == caseClassHash(C6))
assert(C6b.hashCode == caseClassHash(C6b, "C6b"))

val c7 = C7("hi")
val c8 = new C8("hi")
assert(c7.hashCode == caseClassHash(c7))
assert(c7 == c8)
assert(c7.hashCode == c8.hashCode)
assert(c8.hashCode != caseClassHash(c8))
assert(c8.hashCode == caseClassHash(c8, "C7"))


assert(VCC(1).canEqual(VCC(1)))
assert(!VCC(1).canEqual(1))
}
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