Merge pull request scala#5301 from retronym/ticket/SD-167

SD-167 Fine tuning constructor pattern translation

Fixes scala/scala-dev#167

Author: adriaanm

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -1764,7 +1764,7 @@ trait Namers extends MethodSynthesis {
    *  bugs waiting to be reported? If not, why not? When exactly do we need to
    *  call this method?
    */
-  def companionSymbolOf(original: Symbol, ctx: Context): Symbol = {
+  def companionSymbolOf(original: Symbol, ctx: Context): Symbol = if (original == NoSymbol) NoSymbol else {
     val owner = original.owner
     // SI-7264 Force the info of owners from previous compilation runs.
     //         Doing this generally would trigger cycles; that's what we also

src/compiler/scala/tools/nsc/typechecker/PatternTypers.scala

@@ -79,6 +79,7 @@ trait PatternTypers {
       // do not update the symbol if the tree's symbol's type does not define an unapply member
       // (e.g. since it's some method that returns an object with an unapply member)
       val fun         = inPlaceAdHocOverloadingResolution(fun0)(hasUnapplyMember)
+      val canElide    = treeInfo.isQualifierSafeToElide(fun)
       val caseClass   = companionSymbolOf(fun.tpe.typeSymbol.sourceModule, context)
       val member      = unapplyMember(fun.tpe)
       def resultType  = (fun.tpe memberType member).finalResultType
@@ -94,7 +95,7 @@ trait PatternTypers {
       // Dueling test cases: pos/overloaded-unapply.scala, run/case-class-23.scala, pos/t5022.scala
       // A case class with 23+ params has no unapply method.
       // A case class constructor may be overloaded with unapply methods in the companion.
-      if (caseClass.isCase && !member.isOverloaded)
+      if (canElide && caseClass.isCase && !member.isOverloaded)
         logResult(s"convertToCaseConstructor($fun, $caseClass, pt=$pt)")(convertToCaseConstructor(fun, caseClass, pt))
       else if (!reallyExists(member))
         CaseClassConstructorError(fun, s"${fun.symbol} is not a case class, nor does it have an unapply/unapplySeq member")

test/files/run/sd167.check

@@ -0,0 +1 @@
+x

test/files/run/sd167.scala

@@ -0,0 +1,8 @@
+object Test {
+  implicit class ToExtractor(val s: StringContext) {
+    def x = {println("x"); Some }
+  }
+  def main(args: Array[String]) {
+    Some(1) match { case x"${a}" => }  // used to convert to `case Some(a) =>` and omit side effects
+  }
+}