SI-6902 Check unreachability under @unchecked

Only exhaustiveness checking should be disabled if the
scrutinee of a match as annotated as `: @unchecked`.
This was the pre-2.10.x behaviour.

This also fixes a variation of the closed ticket,
SI-6011. The exhaustiveness check is needed to
safely fallback from emitting a table switch if
duplicate cases are detected.

1 files changed, 8 insertions, 9 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala b/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
index fa8aff5cdd..9746b05c03 100644
--- a/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
@@ -3225,6 +3225,7 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
       // TODO: make more fine-grained, as we don't always need to jump
       def canJump: Boolean
 
+      /** Should exhaustivity analysis be skipped? */
       def unchecked: Boolean
 
 
@@ -3458,12 +3459,10 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
             case Some(cds) => cds
           }
 
-          val allReachable = unchecked || {
-            // a switch with duplicate cases yields a verify error,
-            // and a switch with duplicate cases and guards cannot soundly be rewritten to an unguarded switch
-            // (even though the verify error would disappear, the behaviour would change)
-            unreachableCase(caseDefsWithGuards) map (cd => reportUnreachable(cd.body.pos)) isEmpty
-          }
+          // a switch with duplicate cases yields a verify error,
+          // and a switch with duplicate cases and guards cannot soundly be rewritten to an unguarded switch
+          // (even though the verify error would disappear, the behaviour would change)
+          val allReachable = unreachableCase(caseDefsWithGuards) map (cd => reportUnreachable(cd.body.pos)) isEmpty
 
           if (!allReachable) Nil
           else if (noGuards(caseDefsWithGuards)) {
@@ -3710,10 +3709,10 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
                               with SymbolicMatchAnalysis
                               with DPLLSolver { self: TreeMakers =>
     override def optimizeCases(prevBinder: Symbol, cases: List[List[TreeMaker]], pt: Type, unchecked: Boolean): (List[List[TreeMaker]], List[Tree]) = {
+      unreachableCase(prevBinder, cases, pt) foreach { caseIndex =>
+        reportUnreachable(cases(caseIndex).last.pos)
+      }
       if (!unchecked) {
-        unreachableCase(prevBinder, cases, pt) foreach { caseIndex =>
-          reportUnreachable(cases(caseIndex).last.pos)
-        }
         val counterExamples = exhaustive(prevBinder, cases, pt)
         if (counterExamples.nonEmpty)
           reportMissingCases(prevBinder.pos, counterExamples)