SI-5900 Fix pattern inference regression

This commit does not close SI-5900. It only addresses a regression
in 2.11 prereleases caused by SI-7886.

The fix for SI-7886 was incomplete (as shown by the last commit)
and incorrect (as shown by the regression in pos/t5900a.scala and
the fact it ended up inferring type parameters.)

I believe that the key to fixing this problem will be unifying
the inference of case class constructor patterns and extractor
patterns.

I've explored that idea:

  https://gist.github.com/retronym/7704153
  https://github.com/retronym/scala/compare/ticket/5900

But didn't quite get there.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/PatternTypers.scala b/src/compiler/scala/tools/nsc/typechecker/PatternTypers.scala
index 41c656f8ce..cf3f265f0c 100644
--- a/src/compiler/scala/tools/nsc/typechecker/PatternTypers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/PatternTypers.scala
@@ -221,10 +221,12 @@ trait PatternTypers {
      * see test/files/../t5189*.scala
      */
     private def convertToCaseConstructor(tree: Tree, caseClass: Symbol, ptIn: Type): Tree = {
-      def untrustworthyPt = (
+      // TODO SI-7886 / SI-5900 This is well intentioned but doesn't quite hit the nail on the head.
+      //      For now, I've put it completely behind -Xstrict-inference.
+      val untrustworthyPt = settings.strictInference && (
            ptIn =:= AnyTpe
         || ptIn =:= NothingTpe
-        || settings.strictInference && ptIn.typeSymbol != caseClass
+        || ptIn.typeSymbol != caseClass
       )
       val variantToSkolem     = new VariantToSkolemMap
       val caseClassType       = tree.tpe.prefix memberType caseClass
@@ -371,4 +373,4 @@ trait PatternTypers {
       }
     }
   }
-}
\ No newline at end of file
+}