OverridingPairsChecker

We can exclude pairs safely from checking only under three additional conditions

• their signatures also match in the parent class. See neg/i12828.scala for an example where this matters.
• They overriding/overridden appear in linearization order. See neg/i5094.scala for an example where this matters.
• The overridden symbol is not abstract override. For such symbols we need a more extensive test since the virtual super chain depends on the precise linearization order, which might be different for the subclass. See neg/i14415.scala.

Checks the subtype relationship tp1 <:< tp2. It is passed to the checkOverride operation in checkAll, to be used for compatibility checking.

Does sym1 match sym2 so that it qualifies as overriding when both symbols are seen as members of self? Types always match. Term symbols match if their membertypes relative to self do.

A hook that allows to omit override checks between overriding and overridden. Overridden in capture checking to handle non-capture checked classes leniently.

If not null: The symbol overridden by overriding

The current candidate symbol for overriding