Merge pull request #1111 from dotty-staging/fix-#1099

Special case pattern matching against abstract types with class tags

1 files changed, 30 insertions, 14 deletions

diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index e9c641282..8ba155097 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -147,18 +147,7 @@ object desugar {
         tparam
     }
 
-    val meth1 = epbuf.toList match {
-      case Nil =>
-        meth
-      case evidenceParams =>
-        val vparamss1 = vparamss.reverse match {
-          case (vparams @ (vparam :: _)) :: rvparamss if vparam.mods is Implicit =>
-            ((vparams ++ evidenceParams) :: rvparamss).reverse
-          case _ =>
-            vparamss :+ evidenceParams
-        }
-        cpy.DefDef(meth)(tparams = tparams1, vparamss = vparamss1)
-    }
+    val meth1 = addEvidenceParams(cpy.DefDef(meth)(tparams = tparams1), epbuf.toList)
 
     /** The longest prefix of parameter lists in vparamss whose total length does not exceed `n` */
     def takeUpTo(vparamss: List[List[ValDef]], n: Int): List[List[ValDef]] = vparamss match {
@@ -204,6 +193,30 @@ object desugar {
     }
   }
 
+  // Add all evidence parameters in `params` as implicit parameters to `meth` */
+  private def addEvidenceParams(meth: DefDef, params: List[ValDef])(implicit ctx: Context): DefDef =
+    params match {
+      case Nil =>
+        meth
+      case evidenceParams =>
+        val vparamss1 = meth.vparamss.reverse match {
+          case (vparams @ (vparam :: _)) :: rvparamss if vparam.mods is Implicit =>
+            ((vparams ++ evidenceParams) :: rvparamss).reverse
+          case _ =>
+            meth.vparamss :+ evidenceParams
+        }
+        cpy.DefDef(meth)(vparamss = vparamss1)
+    }
+
+  /** The implicit evidence parameters of `meth`, as generated by `desugar.defDef` */
+  private def evidenceParams(meth: DefDef)(implicit ctx: Context): List[ValDef] =
+    meth.vparamss.reverse match {
+      case (vparams @ (vparam :: _)) :: _ if vparam.mods is Implicit =>
+        vparams.dropWhile(!_.name.startsWith(nme.EVIDENCE_PARAM_PREFIX))
+      case _ =>
+        Nil
+    }
+
   /** Fill in empty type bounds with Nothing/Any. Expand private local type parameters as follows:
    *
    *     class C[v T]
@@ -256,10 +269,13 @@ object desugar {
       else constr1.vparamss.nestedMap(toDefParam)
     val constr = cpy.DefDef(constr1)(tparams = constrTparams, vparamss = constrVparamss)
 
-    // Add constructor type parameters to auxiliary constructors
+    // Add constructor type parameters and evidence implicit parameters
+    // to auxiliary constructors
     val normalizedBody = impl.body map {
       case ddef: DefDef if ddef.name.isConstructorName =>
-        cpy.DefDef(ddef)(tparams = constrTparams)
+        addEvidenceParams(
+          cpy.DefDef(ddef)(tparams = constrTparams),
+          evidenceParams(constr1).map(toDefParam))
       case stat =>
         stat
     }