Fix #7698: Disallow quoted patterns against non Expr/Type

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

@@ -337,6 +337,11 @@ trait QuotesAndSplices {
    *  ```
    */
   private def typedQuotePattern(tree: untpd.Quote, pt: Type, qctx: Tree)(implicit ctx: Context): Tree = {
+    if tree.quoted.isTerm && !pt.derivesFrom(defn.QuotedExprClass) then
+      ctx.error("Quote pattern can only match scrutinees of type scala.quoted.Expr", tree.sourcePos)
+    else if tree.quoted.isType && !pt.derivesFrom(defn.QuotedTypeClass) then
+      ctx.error("Quote pattern can only match scrutinees of type scala.quoted.Type", tree.sourcePos)
+
     val quoted = tree.quoted
     val exprPt = pt.baseType(if quoted.isType then defn.QuotedTypeClass else defn.QuotedExprClass)
     val quotedPt = exprPt.argInfos.headOption match {

tests/neg/i7698.scala

@@ -0,0 +1,14 @@
+import scala.quoted._
+import scala.quoted.matching._
+
+trait Show[T] {
+  def show(x: T): String
+}
+
+def showInterpolatorImpl(sc: Expr[StringContext], argsExpr: Expr[Seq[Any]])(using qctx: QuoteContext): Expr[String] =
+  argsExpr.unseal match
+    case '{ $arg: $t } => // error
+    case '[ Int ] => // error
+  ???
+
+inline def (sc: => StringContext) show (args: Any*): String = ${ showInterpolatorImpl('sc, 'args) }

tests/pos/i6998.scala

@@ -1,5 +1,5 @@
 import scala.quoted._
 
 def foo(using QuoteContext) : Unit = {
-  val '{ $f : (Int => Double) } = ???
+  val '{ $f : (Int => Double) } = ??? : Expr[Any]
 }