TASTy generated for AnyVal with non-val param is invalid

[sjrd]

Compiler version

3.3.1

Minimized code

class ValueClassNonVal(self: String) extends AnyVal:
  def get: String = self // TERMREFsymbol, OK
  def getThroughThis: String = this.self // SELECT, ~OK because this prefix

  // def getOther(that: ValueClassNonVal): String = that.self // does not compile, rightly so

  // <generated>
  def equals(x$0: Any): Boolean = x$0 match
    case x$0: ValueClassNonVal =>
      this.self // SELECT, ~OK because this prefix
        == x$0.self // SELECT, definitely not OK
    case _ =>
      false
end ValueClassNonVal

Output

    80:       DEFDEF(73) 20 [equals]
    83:         PARAM(5) 21 [x$0]
    86:           TYPEREF 22 [Any]
    88:             SHAREDtype 19
    90:         TYPEREF 23 [Boolean]
    92:           SHAREDtype 19
    94:         MATCH(57)
    96:           TERMREFdirect 83
    98:           CASEDEF(46)
   100:             BIND(26) 21 [x$0]
   103:               SHAREDtype 70
   105:               TYPED(20)
   107:                 IDENT 24 [_]
   109:                   ANNOTATEDtype(14)
   111:                     SHAREDtype 70
   113:                     APPLY(10)
   115:                       SELECTin(8) 27 [<init>[Signed Signature(List(),scala.unchecked) @<init>]]
   118:                         NEW
   119:                           TYPEREF 25 [unchecked]
   121:                             SHAREDtype 19
   123:                         SHAREDtype 119
   125:                 SHAREDtype 109
   127:               SYNTHETIC
   128:             APPLY(16)
   130:               SELECTin(10) 30 [==[Signed Signature(List(java.lang.Object),scala.Boolean) @==]]
   133:                 SELECT 3 [self]
   135:                   QUALTHIS
   136:                     IDENTtpt 2 [ValueClassNonVal]
   138:                       SHAREDtype 70
   140:                 SHAREDtype 86
   142:               SELECT 3 [self] // <-- PROBLEM HERE
   144:                 TERMREFdirect 100
   146:           CASEDEF(5)
   148:             IDENT 24 [_]
   150:               SHAREDtype 86
   152:             FALSEconst
   153:         OVERRIDE
   154:         SYNTHETIC

Normally, a SELECT cannot point to a PRIVATE | LOCAL field. There is an exception if the prefix is a ThisType, to be able to access local params from my own class. But it is not possible to refer to a PRIVATE | LOCAL field through any other prefix.

Here, the TASTy that gets generated does precisely the thing that's not possible. In fact, if we try to write the code by hand, it does not compile.

Expectation

Either the self param should not have the LOCAL flag, or the generated equals method should use another way of accessing that value.

[SethTisue]

This is legal? On purpose? It's illegal in Scala 2. https://scala-lang.org/api/3.x/scala/AnyVal.html still says "must have a single val parameter that is the underlying runtime representation"

Perhaps there's some rationale and this just went by me, but I'm especially surprised since https://docs.scala-lang.org/overviews/core/value-classes.html says

In Scala 3, value classes are still supported for compatibility reasons

so it seems odd that any Scala 2 restrictions would have been lifted.

Sorry if this is a tangent, but I'm bringing it up here on the chance that it was not intended to even allow this.

[sjrd]

I have a very vague recollection that it was intentionally made valid, but clearly we did not foresee this issue with equals. The best course of action might indeed be to outlaw that.