Thoughts on TASTy grammar

[cache-nez]

This is the list of my impressions from working with the TASTy grammar, which can hopefully be useful for an eventual discussion of TASTy. Additions are welcome.

• It is hard to recover the type of a parent because of the surrounding Apply / Block, representing the call to the constructor
• package is sometimes referenced in a special way: as `THIS TYPEREFpkg ` rather than `TERMREFpkg `
• if a MATCHtpt has a BIND(_) inside, the bound ident is represented as IDENT (rather than IDENTtpt) even though it represents a type
• at the phase when TASTy is produced, we probably already know which of the parents SUPER refers to. However, this is not included in .tasty file. Perhaps this can be included to avoid re-resolution.

[sjrd]

New thing: DefDefs don't have a SignedName at definition site. It needs to be recomputed from the erasure, which requires dereferencing all the types in the signautre.

[sjrd]

TermRefs for private (and even local like non-val constructor param) members should always be TERMREFsymbols, so that name-based field selection can systematically filter out Private and be done with it. private members are never accessible from another .tasty file, so we always have access to the symbol.

[sjrd]

SuperTypes should not exist at all. They may have had a reason to exist when it was possible to shadow an inherited class with another class, but that is not allowed in Scala 3 anymore.

Super nodes should not exist as a dedicated thing. They should be fused with their enclosing Select as SuperSelect, and be reserved to term selection.

[sjrd]

https://github.com/lampepfl/dotty/issues/19307

The param of AnyVal classes should never have the LOCAL flag, because it gets automatically accessed on another instance in the generated equals method. Example:

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