Insert top level type variables before typing quote pattern

```scala
case '{ type u; ($x: t, $y: t, $z: u) }
```
is desugared to
```scala
case '{ type t; type u; ($x: `t`, $y: `t`, $z: `u`) }
```

Fixes scala#14708

Author: nicolasstucki

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -1518,7 +1518,7 @@ object Trees {
         paramss.mapConserve(transformParams)
 
       protected def transformMoreCases(tree: Tree)(using Context): Tree = {
-        assert(ctx.reporter.errorsReported)
+        assert(ctx.reporter.errorsReported, tree)
         tree
       }
     }

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

@@ -10,6 +10,7 @@ import dotty.tools.dotc.core.Contexts._
 import dotty.tools.dotc.core.Decorators._
 import dotty.tools.dotc.core.Flags._
 import dotty.tools.dotc.core.NameKinds.PatMatGivenVarName
+import dotty.tools.dotc.core.NameOps.isVarPattern
 import dotty.tools.dotc.core.Names._
 import dotty.tools.dotc.core.StagingContext._
 import dotty.tools.dotc.core.StdNames._
@@ -24,7 +25,6 @@ import dotty.tools.dotc.util.Stats.record
 import dotty.tools.dotc.reporting.IllegalVariableInPatternAlternative
 import scala.collection.mutable
 
-
 /** Type quotes `'{ ... }` and splices `${ ... }` */
 trait QuotesAndSplices {
   self: Typer =>
@@ -394,9 +394,84 @@ trait QuotesAndSplices {
     }
     val quoted0 = desugar.quotedPattern(quoted, untpd.TypedSplice(TypeTree(quotedPt)))
     val quoteCtx = quoteContext.addMode(Mode.QuotedPattern).retractMode(Mode.Pattern)
+
+    def normalizeTypeBindings(quoted: untpd.Tree): untpd.Tree =
+      val variables = mutable.Set.empty[TypeName] // TODO use stable order
+      def normalizeType(tpt: untpd.Tree): untpd.Tree =
+        new untpd.UntypedTreeMap {
+          override def transform(tpt: untpd.Tree)(using Context) =
+            tpt match
+              case untpd.Ident(tpnme.WILDCARD_STAR) => tpt
+              case tpt @ untpd.Ident(name) if !tpt.isBackquoted && name.isVarPattern =>
+                variables += name.asTypeName
+                tpt.pushAttachment(Trees.Backquoted, ())
+                tpt
+              case _: untpd.TypedSplice => tpt
+              case _ =>
+                super.transform(tpt)
+        }.transform(tpt)
+      val transformed: untpd.Tree = new untpd.UntypedTreeMap {
+          override def transform(tree: untpd.Tree)(using Context) =
+            // println("- " + tree.show)
+            // println("- " + tree)
+            tree match
+              case untpd.Splice(_) => tree
+              case untpd.Typed(expr, tpt) =>
+                untpd.cpy.Typed(tree)(
+                  super.transform(expr),
+                  normalizeType(tpt)
+                )
+              case untpd.TypeApply(fn, targs) =>
+                untpd.cpy.TypeApply(tree)(
+                  super.transform(fn),
+                  targs.map(normalizeType)
+                )
+              case _ => super.transform(tree)
+      }.transform(quoted)
+
+      def typeBindingDefinedInSource: List[TypeName] =
+        transformed match
+          case untpd.Block(stats, _) =>
+            stats.takeWhile {
+              case untpd.TypeDef(name, _) => name.isVarPattern
+              case _ => false
+            }.map(_.asInstanceOf[untpd.TypeDef].name.asTypeName)
+          case _ => Nil
+      variables --= typeBindingDefinedInSource
+
+      // println("==============")
+      // println(quoted.show)
+      // println(quoted)
+      // println("--------------")
+      // println(transformed.show)
+      // println(transformed)
+      // println(" ")
+      // println(variables)
+      // println(" ")
+
+      if variables.isEmpty then transformed
+      else
+        transformed match
+          case untpd.Block(stats, expr) =>
+            val typeBindings = stats.takeWhile {
+              case untpd.TypeDef(name, _) => name.isVarPattern
+              case _ => false
+            }
+            variables --= typeBindings.map(_.asInstanceOf[untpd.TypeDef].name.asTypeName)
+            untpd.cpy.Block(quoted)(
+              variables.toList.map(name => untpd.TypeDef(name, untpd.TypeBoundsTree(untpd.EmptyTree, untpd.EmptyTree, untpd.EmptyTree))) ::: stats,
+              expr
+            )
+          case _ =>
+            untpd.cpy.Block(quoted)(
+              variables.toList.map(name => untpd.TypeDef(name, untpd.TypeBoundsTree(untpd.EmptyTree, untpd.EmptyTree, untpd.EmptyTree))),
+              transformed
+            )
+
+    val quoted0normalized = normalizeTypeBindings(quoted0)
     val quoted1 =
-      if quoted.isType then typedType(quoted0, WildcardType)(using quoteCtx)
-      else typedExpr(quoted0, WildcardType)(using quoteCtx)
+      if quoted.isType then typedType(quoted0normalized, WildcardType)(using quoteCtx)
+      else typedExpr(quoted0normalized, WildcardType)(using quoteCtx)
 
     val (typeBindings, shape, splices) = splitQuotePattern(quoted1)
 

tests/neg-macros/quotedPatterns-5.scala

@@ -2,7 +2,7 @@ import scala.quoted.*
 object Test {
   def test(x: quoted.Expr[Int])(using Quotes): Unit = x match {
     case '{ type t; 4 } => Type.of[t]
-    case '{ type t; poly[t]($x); 4 } => // error: duplicate pattern variable: t
+    case '{ type t; poly[t]($x); 4 } =>
     case '{ type `t`; poly[`t`]($x); 4 } =>
       Type.of[t] // error
     case _ =>

tests/pos-macros/i14708.scala

@@ -0,0 +1,18 @@
+import scala.quoted.*
+
+object Main {
+  def foo(a: Expr[Any])(using Quotes) = {
+    a match {
+      case '{ ($x: Set[t]).toSet } =>
+      case '{ ($x: Set[t]).toSet[t] } =>
+      case '{ val a = 1; a; ($x: Set[t]).toSet } =>
+      case '{ type u; ($x: Set[`u`]).toSet } =>
+      case '{ type t; ($x: Set[t]).toSet } =>
+      case '{ varargs(${_}*) } =>
+      case '{ type u; ($x: t, $y: t, $z: u) } =>
+      case _ =>
+    }
+  }
+}
+
+def varargs(x: Any*): Unit = ()