`MatchTypeNoCases` is no longer emitted

[WojciechMazur]

MatchTypeNoCases error defined at

scala3/compiler/src/dotty/tools/dotc/reporting/messages.scala

Lines 3311 to 3314 in f67a1a0

	class MatchTypeNoCases(casesText: String)(using Context) extends TypeMsg(MatchTypeNoCasesID):
	def msg(using Context) = i"Match type reduction $casesText"
	def explain(using Context) = ""

originally used in

scala3/compiler/src/dotty/tools/dotc/core/TypeComparer.scala

Lines 3955 to 3963 in f67a1a0

	case Nil =>
	/* TODO warn ? then re-enable warn/12974.scala:26
	val noCasesText = MatchTypeTrace.noMatchesText(scrut, cases)
	report.warning(reporting.MatchTypeNoCases(noCasesText), pos = ???)
	*/
	MatchTypeTrace.noMatches(scrut, cases)
	NoType
	inFrozenConstraint(recur(cases))

is still commented out. It makes this error code effectively inactive.

The mentioned test is still commented out

scala3/tests/warn/12974.scala

Lines 22 to 34 in f67a1a0

	def main(args: Array[String]) =
	import Record._
	val foo: Any = Rec.empty.fetch("foo") // TODO
	// ^
	// Match type reduction failed since selector EmptyTuple.type
	// matches none of the cases
	//
	// case (("foo" : String), t) *: _ => t
	// case _ *: t => example.RecMap.Record.Rec.HasKey[t, ("foo" : String)]
	end main

Compiler version

3.7.4
3.8.1-nightly

Expectation

It's been almost 2 years since this error message was suppressed we should either restore the original mechanism or make the error formally inactive.

Maybe related discussion in #23822