blackbox restriction #4: can't customize pattern matching

When an application of a blackbox macro is used as an extractor in a
pattern match, it triggers an unconditional compiler error,
preventing customizations of pattern matching implemented with macros.

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

@@ -409,9 +409,10 @@ trait PatternTypers {
 
       if (fun1.tpe.isErroneous)
         duplErrTree
-      else if (unapplyMethod.isMacro && !fun1.isInstanceOf[Apply])
-        duplErrorTree(WrongShapeExtractorExpansion(tree))
-      else
+      else if (unapplyMethod.isMacro && !fun1.isInstanceOf[Apply]) {
+        if (isBlackbox(unapplyMethod)) duplErrorTree(BlackboxExtractorExpansion(tree))
+        else duplErrorTree(WrongShapeExtractorExpansion(tree))
+      } else
         makeTypedUnApply()
     }
 

test/files/neg/macro-blackbox-extractor.check

@@ -0,0 +1,4 @@
+Test_2.scala:3: error: extractor macros can only be whitebox
+    case Extractor(x) => println(x)
+                  ^
+one error found

test/files/neg/macro-blackbox-extractor/Macros_1.scala

@@ -0,0 +1,21 @@
+import scala.reflect.macros.BlackboxContext
+import language.experimental.macros
+
+object Extractor {
+  def unapply(x: Int) = macro Macros.unapplyImpl
+}
+
+object Macros {
+  def unapplyImpl(c: BlackboxContext)(x: c.Tree) = {
+    import c.universe._
+    q"""
+      new {
+        class Match(x: Int) {
+          def isEmpty = false
+          def get = x
+        }
+        def unapply(x: Int) = new Match(x)
+      }.unapply($x)
+    """
+  }
+}

test/files/neg/macro-blackbox-extractor/Test_2.scala

@@ -0,0 +1,5 @@
+object Test extends App {
+  42 match {
+    case Extractor(x) => println(x)
+  }
+}

test/files/neg/t5903d.check

@@ -1,4 +1,4 @@
-Test_2.scala:4: error: extractor macros can only expand into extractor calls
+Test_2.scala:4: error: extractor macros can only be whitebox
     case t"$x" => println(x)
          ^
 one error found

test/files/run/macro-whitebox-extractor.check

@@ -0,0 +1 @@
+42

test/files/run/macro-whitebox-extractor/Macros_1.scala

@@ -0,0 +1,21 @@
+import scala.reflect.macros.WhiteboxContext
+import language.experimental.macros
+
+object Extractor {
+  def unapply(x: Int) = macro Macros.unapplyImpl
+}
+
+object Macros {
+  def unapplyImpl(c: WhiteboxContext)(x: c.Tree) = {
+    import c.universe._
+    q"""
+      new {
+        class Match(x: Int) {
+          def isEmpty = false
+          def get = x
+        }
+        def unapply(x: Int) = new Match(x)
+      }.unapply($x)
+    """
+  }
+}

test/files/run/macro-whitebox-extractor/Test_2.scala

@@ -0,0 +1,5 @@
+object Test extends App {
+  42 match {
+    case Extractor(x) => println(x)
+  }
+}