Commits on Dec 22, 2022

1. Don't GLB binders of type patterns, use the type directly …

   In type patterns `c match { case x: T }`, the translation would assign
   the GLB of `c`'s type and `T` to the varaible `x`.
   
   This seems to trace back to the first version of the "virtual pattern
   matcher". I could not find a similar use of `glb` in that revision
   of the codebase. So I'm not sure if it was a new addition, or picked
   up from the previous implementation.
   
   https://github.com/scala/scala/blob/8a9fd64129926eea35f7dca181242855f14e153f/src/compiler/scala/tools/nsc/typechecker/PatMatVirtualiser.scala#L438-L440
   
   In the test case, the GLB collapsed to `Null` because its
   computation failed (combination of f-bounds, existentials, skolems that
   I don't follow), see `throw GlbFailure`. This is how it's been for 14
   years (b894f80). This resulted in a cast to `Null$` failing at
   runtime.
   
   I assume GLB is fixed in Scala 3, as this core of the type system has
   a new implementation. But the test case as such doesn't compile in
   Scala 3 due to the non-wildcard existential.

   

   lrytz committed Dec 22, 2022
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