[WIP] Report TypeError for match type with no case or uninhabited scrutinee
#19964
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This reverts commit 9ae1598 Note that the changes in Typer: ``` val unsimplifiedType = result.tpe simplify(result, pt, locked) result.tpe.stripTypeVar match case e: ErrorType if !unsimplifiedType.isErroneous => errorTree(xtree, e.msg, xtree.srcPos) case _ => result ``` cannot be reverted yet since the MatchReducer now also reduces to an `ErrorType` for MatchTypeLegacyPatterns, introduced after 9ae1598.
i18488.scala was only passing because of the bug in the MatchReducer,
as we can see in the subtyping trace:
```
==> isSubType TableQuery[BaseCrudRepository.this.EntityTable] <:< Query[BaseCrudRepository.this.EntityTable, E[Option]]?
==> isSubType Query[BaseCrudRepository.this.EntityTable, Extract[BaseCrudRepository.this.EntityTable]] <:<
Query[BaseCrudRepository.this.EntityTable, E[Option]] (left is approximated)?
==> isSubType E[Option] <:< Extract[BaseCrudRepository.this.EntityTable]?
==> isSubType [T[_$1]] =>> Any <:< Extract?
==> isSubType Any <:< Extract[T]?
==> isSubType Any <:< T match { case AbstractTable[t] => t } <: t (right is approximated)?
==> isSubType Any <:< <error Match type reduction failed since selector T
matches none of the cases
case AbstractTable[t] => t> (right is approximated)?
<== isSubType Any <:< <error Match type reduction failed since selector T
matches none of the cases
case AbstractTable[t] => t> (right is approximated) = true
<== isSubType Any <:< T match { case AbstractTable[t] => t } <: t (right is approximated) = true
<== isSubType Any <:< Extract[T] = true
<== isSubType [T[_$1]] =>> Any <:< Extract = true
...
<== isSubType Extract[BaseCrudRepository.this.EntityTable] <:< E[Option] = true
<== isSubType Query[BaseCrudRepository.this.EntityTable, Extract[BaseCrudRepository.this.EntityTable]] <:<
Query[BaseCrudRepository.this.EntityTable, E[Option]] (left is approximated) = true
<== isSubType TableQuery[BaseCrudRepository.this.EntityTable] <:< Query[BaseCrudRepository.this.EntityTable, E[Option]] = true
```
The comment in 8778.scala:21 was outdated `Test.M[Inv[Int & String]]` did not reduce to `String` but was left unreduced So getting an error now is consistent with that But one should probably investigate why we find `Inv[Int & String]` is uninhabited whereas `Inv[Nothing]` is fine
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Based #19953
Implements suggestion from #19954 (comment)
Fixes #19949
Fixes #19950
See #19949 (comment) for summary of options