Mix in the productPrefix hash statically in case class hashCode
#22865
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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.
sjrd
approved these changes
Mar 24, 2025
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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(scala/bug#13033).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.Scala 3 forward port of scala/scala#11023