Fix #16615 - crashes of path dependent types in spliced Type.of (#16773)

Fixes #16615

Previously it was assumed that the type in Type.of could be captured as
a whole, which meant that path dependent types for which a separate
@SplicedType hole definitions were included in a block, would end up
with missing references.

Now when find a block in Type.of, we try to analise all parts of the
type separately, adding additional hole definitions to the block as
necessary.
For types that can be captured as a whole (those which did not have a
block generated previously, meaning they do not include any @SplicedType
hole definitions), old method is used.

In essence, ended up replicating the trees proposed in the original
issue thread, which were incredibly helpful.

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

@@ -242,9 +242,16 @@ class Splicing extends MacroTransform:
                 else args.mapConserve(arg => transformLevel0QuoteContent(arg)(using quoteContext))
               }
               cpy.Apply(tree)(cpy.Select(sel)(cpy.Apply(app)(fn, newArgs), nme.apply), quotesArgs)
-        case Apply(TypeApply(_, List(tpt)), List(quotes))
+        case Apply(TypeApply(typeof, List(tpt)), List(quotes))
         if tree.symbol == defn.QuotedTypeModule_of && containsCapturedType(tpt.tpe) =>
-          ref(capturedType(tpt))(using ctx.withSource(tree.source)).withSpan(tree.span)
+          val newContent = capturedPartTypes(tpt)
+          newContent match
+            case block: Block => 
+              inContext(ctx.withSource(tree.source)) {
+                Apply(TypeApply(typeof, List(newContent)), List(quotes)).withSpan(tree.span)
+              }
+            case _ =>
+              ref(capturedType(newContent))(using ctx.withSource(tree.source)).withSpan(tree.span)
         case CapturedApplication(fn, argss) =>
           transformCapturedApplication(tree, fn, argss)
         case _ =>
@@ -335,17 +342,46 @@ class Splicing extends MacroTransform:
       val bindingSym = refBindingMap.getOrElseUpdate(tree.symbol, (tree, newBinding))._2
       ref(bindingSym)
 
-    private def capturedType(tree: Tree)(using Context): Symbol =
-      val tpe = tree.tpe.widenTermRefExpr
-      def newBinding = newSymbol(
+    private def newQuotedTypeClassBinding(tpe: Type)(using Context) = 
+      newSymbol(
         spliceOwner,
         UniqueName.fresh(nme.Type).toTermName,
         Param,
         defn.QuotedTypeClass.typeRef.appliedTo(tpe),
       )
-      val bindingSym = refBindingMap.getOrElseUpdate(tree.symbol, (TypeTree(tree.tpe), newBinding))._2
+
+    private def capturedType(tree: Tree)(using Context): Symbol =
+      val tpe = tree.tpe.widenTermRefExpr
+      val bindingSym = refBindingMap
+        .getOrElseUpdate(tree.symbol, (TypeTree(tree.tpe), newQuotedTypeClassBinding(tpe)))._2
       bindingSym
 
+    private def capturedPartTypes(tpt: Tree)(using Context): Tree =
+      val old = healedTypes
+      healedTypes = PCPCheckAndHeal.QuoteTypeTags(tpt.span)
+      val capturePartTypes = new TypeMap {
+        def apply(tp: Type) = tp match {
+          case typeRef @ TypeRef(prefix, _) if isCaptured(prefix.typeSymbol) || isCaptured(prefix.termSymbol) =>
+            val termRef = refBindingMap
+              .getOrElseUpdate(typeRef.symbol, (TypeTree(typeRef), newQuotedTypeClassBinding(typeRef)))._2.termRef
+            val tagRef = healedTypes.nn.getTagRef(termRef)
+            tagRef
+          case _ =>
+            mapOver(tp)
+        }
+      }
+      val captured = capturePartTypes(tpt.tpe.widenTermRefExpr)
+      val newHealedTypes = healedTypes.nn.getTypeTags
+      healedTypes = old
+      tpt match
+        case block: Block =>
+          cpy.Block(block)(newHealedTypes ::: block.stats, TypeTree(captured))
+        case _ => 
+          if newHealedTypes.nonEmpty then
+            cpy.Block(tpt)(newHealedTypes, TypeTree(captured))
+          else
+            tpt
+
     private def getTagRefFor(tree: Tree)(using Context): Tree =
       val capturedTypeSym = capturedType(tree)
       TypeTree(healedTypes.nn.getTagRef(capturedTypeSym.termRef))

tests/pos-macros/i16615.scala

@@ -0,0 +1,19 @@
+import scala.quoted.*
+
+trait Api:
+  type Reader[E]
+
+def bugImpl[T: Type, Q[_]: Type](using Quotes) =
+  '{
+    val p: Api = ???
+    ${
+      Type.of[p.Reader[T]]
+      Type.of[Q[p.Reader[T]]]
+      Type.of[p.Reader[Q[p.Reader[T]]]]
+      Type.of[List[p.Reader[T]]]
+      Type.of[p.Reader[List[p.Reader[T]]]]
+      Type.of[p.Reader[List[T]]]
+      Type.of[p.Reader[Q[T]]]
+      Expr(1)
+    }
+  }