Fix #6325: Propagate error type to internal splice

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

@@ -1181,7 +1181,9 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   /** An extractor for typed splices */
   object Splice {
     def apply(tree: Tree)(implicit ctx: Context): Tree = {
-      val argType = tree.tpe.baseType(defn.QuotedExprClass).argTypesHi.head
+      val argType =
+        if (tree.tpe.widen.isError) tree.tpe.widen
+        else tree.tpe.baseType(defn.QuotedExprClass).argTypesHi.head
       ref(defn.InternalQuoted_exprSplice).appliedToType(argType).appliedTo(tree)
     }
     def unapply(tree: Tree)(implicit ctx: Context): Option[Tree] = tree match {

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

@@ -2011,12 +2011,16 @@ class Typer extends Namer
         typed(innerExpr, pt)
       case expr =>
         if (ctx.mode.is(Mode.QuotedPattern) && level == 1) {
-          fullyDefinedType(pt, "quoted pattern selector", tree.span)
-          def spliceOwner(ctx: Context): Symbol =
-            if (ctx.mode.is(Mode.QuotedPattern)) spliceOwner(ctx.outer) else ctx.owner
-          val pat = typedPattern(expr, defn.QuotedExprType.appliedTo(pt))(
-            spliceContext.retractMode(Mode.QuotedPattern).withOwner(spliceOwner(ctx)))
-          Splice(pat)
+          if (isFullyDefined(pt, ForceDegree.all)) {
+            def spliceOwner(ctx: Context): Symbol =
+              if (ctx.mode.is(Mode.QuotedPattern)) spliceOwner(ctx.outer) else ctx.owner
+            val pat = typedPattern(expr, defn.QuotedExprType.appliedTo(pt))(
+              spliceContext.retractMode(Mode.QuotedPattern).withOwner(spliceOwner(ctx)))
+            Splice(pat)
+          } else {
+            ctx.error(i"Type must be fully defined.\nConsider annotating the splice using a type ascription:\n  ($tree: XYZ).", expr.sourcePos)
+            tree.withType(UnspecifiedErrorType)
+          }
         }
         else
           typedApply(untpd.Apply(untpd.ref(defn.InternalQuoted_exprSpliceR), tree.expr), pt)(spliceContext).withSpan(tree.span)

tests/neg/i6324.scala

@@ -0,0 +1,6 @@
+class Test {
+  def res(x: quoted.Expr[Int]) given tasty.Reflection: quoted.Expr[Int] = x match {
+    case '{ 1 + $b } => // error: Type must be fully defined. Consider annotating the splice using a type ascription: (${b}: XYZ).
+      b // error: Not found: b
+  }
+}

tests/neg/i6325.scala

@@ -0,0 +1,7 @@
+//import scala.quoted.matching.Bind
+object Test {
+  def res(x: quoted.Expr[Int]) given tasty.Reflection: quoted.Expr[Int] = x match {
+    case '{ 1 + (${Bind(b)}: Int) } => ??? // error: Not found: Bind
+    case _ => ???
+  }
+}