From ecee4985ae982612232d84235553978ccbdbe105 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Sun, 8 Mar 2020 17:57:52 +0100
Subject: [PATCH] Fix #7698: Disallow quoted patterns against non Expr/Type

---
 .../dotty/tools/dotc/typer/QuotesAndSplices.scala  |  5 +++++
 tests/neg/i7698.scala                              | 14 ++++++++++++++
 tests/pos/i6998.scala                              |  2 +-
 3 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg/i7698.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala b/compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala
index e813b87c978f..92e3e4ef188a 100644
--- a/compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala
+++ b/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 {
diff --git a/tests/neg/i7698.scala b/tests/neg/i7698.scala
new file mode 100644
index 000000000000..a71b53a6267e
--- /dev/null
+++ b/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) }
diff --git a/tests/pos/i6998.scala b/tests/pos/i6998.scala
index e87f45166368..41b34d785c23 100644
--- a/tests/pos/i6998.scala
+++ b/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]
 }