Mix in the productPrefix hash statically in case class hashCode
#11023
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The attemt to keep Not sure if that's a big issue... |
This was referenced Mar 20, 2025
sjrd
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Mar 20, 2025
src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
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classOf[C].getName instead of productPrefix in case hashCodeproductPrefix hash statically in case class hashCode
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Since 2.13, case class `hashCode` mixes in the hash code of the `productPrefix` string. This is inconsistent with the `equals` method, subclasses of case classes that override `productPrefix` compare equal but have a different `hashCode`. This commit changes `hashCode` to mix in the `productPrefix.hashCode` statically instead of invoking `productPrefix` at runtime. For case classes without primitive fields, the synthetic `hashCode` invokes `ScalaRunTime._hashCode`, which mixes in the result of `productPrefix`. To fix that, the synthetic hashCode is changed to invoke `MurmurHash3.productHash` directly and mix in the name to the seed statically. This works out with keeping `productHash` forwards and backwards compatible. The `MurmurHash3.productHash` method is deprecated / renamed to `caseClassHash`. This method computes the same hash as the synthetic `hashCode`, except for the corner case where a case class (or a subclass) override the `productPrefix`. In this case, the case class name needs to be passed manually to `caseClassHash`.
som-snytt
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Mar 24, 2025
| } else { | ||
| if (arr == 0) | ||
| if (!ignorePrefix) x.productPrefix.hashCode else seed | ||
| else { |
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rare case where I would retain extra braces (Scala 2)
som-snytt
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Mar 24, 2025
| @@ -152,10 +152,16 @@ object ScalaRunTime { | |||
| // More background at ticket #2318. | |||
| def ensureAccessible(m: JMethod): JMethod = scala.reflect.ensureAccessible(m) | |||
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| // This is called by the synthetic case class `toString` method. | |||
| // It originally had a `CaseClass` parameter type which was changed to `Product`. | |||
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"originally" here means like first verse of Genesis
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…22865) Since 2.13, case class `hashCode` mixes in the hash code of the `productPrefix` string. This is inconsistent with the `equals` method, subclasses of case classes that override `productPrefix` compare equal but have a different `hashCode` (scala/bug#13033). This commit changes `hashCode` to mix in the `productPrefix.hashCode` statically instead of invoking `productPrefix` at runtime. For case classes without primitive fields, the synthetic `hashCode` invokes `ScalaRunTime._hashCode`, which mixes in the result of `productPrefix`. To fix that, the synthetic hashCode is changed to invoke `MurmurHash3.productHash` directly and mix in the name to the seed statically. Scala 3 forward port of scala/scala#11023
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Mix in the `productPrefix` hash statically in case class `hashCode`
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Mix in the `productPrefix` hash statically in case class `hashCode`
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Since 2.13, case class
hashCodemixes in the hash code of theproductPrefixstring. This is inconsistent with theequalsmethod, subclasses of case classes that overrideproductPrefixcompare equal but have a differenthashCode.This commit changes
hashCodeto mix in theproductPrefix.hashCodestatically instead of invokingproductPrefixat runtime.For case classes without primitive fields, the synthetic
hashCodeinvokesScalaRunTime._hashCode, which mixes in the result ofproductPrefix. To fix that, the synthetic hashCode is changed to invokeMurmurHash3.productHashdirectly and mix in the name to the seed statically. This works out with keepingproductHashforwards and backwards compatible.The
MurmurHash3.productHashmethod is deprecated / renamed tocaseClassHash. This method computes the same hash as the synthetichashCode, except for the corner case where a case class (or a subclass) override theproductPrefix. In this case, the case class name needs to be passed manually tocaseClassHash.Fixes scala/bug#13033