Detect non Expr[..] splice patterns

compiler/src/dotty/tools/dotc/quoted/QuotePatterns.scala

@@ -28,7 +28,9 @@ object QuotePatterns:
   /** Check for restricted patterns */
   def checkPattern(quotePattern: QuotePattern)(using Context): Unit = new tpd.TreeTraverser {
     def traverse(tree: Tree)(using Context): Unit = tree match {
-      case _: SplicePattern =>
+      case tree: SplicePattern =>
+        if !tree.body.typeOpt.derivesFrom(defn.QuotedExprClass) then
+          report.error(i"Splice pattern must match an Expr[...]", tree.body.srcPos)
       case tdef: TypeDef if tdef.symbol.isClass =>
         val kind = if tdef.symbol.is(Module) then "objects" else "classes"
         report.error(em"Implementation restriction: cannot match $kind", tree.srcPos)

tests/neg-macros/i19941.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg-macros/i19941.scala:7:14 ---------------------------------------------------------------------------
+7 |    case '{ ${hd *: tl} : *:[Int, EmptyTuple] } => '{ ??? } // error
+  |              ^^^^^^^^
+  |              Splice pattern must match an Expr[...]

tests/neg-macros/i19941.scala

@@ -0,0 +1,7 @@
+import scala.quoted.*
+
+inline def expandMacro(inline from: Tuple): Any = ${ expandMacroImpl }
+
+def expandMacroImpl(using Quotes): Expr[?] =
+  '{ 1 *: EmptyTuple } match
+    case '{ ${hd *: tl} : *:[Int, EmptyTuple] } => '{ ??? } // error

tests/pos-macros/quotedPatterns-4.scala → tests/neg-macros/quotedPatterns-4.scala

@@ -3,7 +3,7 @@ object Test {
   def impl(receiver: Expr[StringContext])(using qctx: scala.quoted.Quotes) = {
     import quotes.reflect.Repeated
     receiver match {
-      case '{ StringContext(${Repeated(parts, tpt)}*) } => // now OK
+      case '{ StringContext(${Repeated(parts, tpt)}*) } => // error: Repeated is not an Expr pattern
     }
   }
 }