Fix #4493: Use captured macro type parameters refrences

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/ReifyQuotes.scala

@@ -120,7 +120,7 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
      *
      *  See `isCaptured`
      */
-    val capturers = new mutable.HashMap[Symbol, RefTree => Tree]
+    val capturers = new mutable.HashMap[Symbol, Tree => Tree]
   }
 
   /** The main transformer class
@@ -144,6 +144,9 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
     /** We are in a `~(...)` context that is not shadowed by a nested `'(...)` */
     def inSplice = outer != null && !inQuote
 
+    /** We are not in a `~(...)` or a `'(...)` */
+    def isRoot = outer != null
+
     /** A map from type ref T to expressions of type `quoted.Type[T]`".
      *  These will be turned into splices using `addTags` and represent type variables
      *  that can be possibly healed.
@@ -291,6 +294,8 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
         else i"${sym.name}.this"
       if (!isThis && sym.maybeOwner.isType && !sym.is(Param))
         check(sym.owner, sym.owner.thisType, pos)
+      else if (level == 1 && sym.isType && sym.is(Param) && sym.owner.is(Macro) && outer.isRoot)
+        importedTags(sym.typeRef) = capturers(sym)(ref(sym))
       else if (sym.exists && !sym.isStaticOwner && !levelOK(sym))
         for (errMsg <- tryHeal(tp, pos))
           ctx.error(em"""access to $symStr from wrong staging level:

tests/pos/i4493-b.scala

@@ -0,0 +1,7 @@
+class Index[K]
+object Index {
+  inline def succ[K](x: K): Unit = ~{
+    implicit val t: quoted.Type[K] = '[K]
+    '(new Index[K])
+  }
+}

tests/pos/i4493-c.scala

@@ -0,0 +1,6 @@
+class Index[K]
+object Index {
+  inline def succ[K]: Unit = ~{
+    '(new Index[K])
+  }
+}

tests/pos/i4493.scala

@@ -0,0 +1,7 @@
+class Index[K]
+object Index {
+  inline def succ[K]: Unit = ~{
+    implicit val t: quoted.Type[K] = '[K]
+    '(new Index[K])
+  }
+}