Fix HOAS pattern example and error message (#19655)

Fixes #19342

Author: nicolasstucki

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -764,7 +764,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         val spliceTypeText = (keywordStr("[") ~ toTextGlobal(tree.typeOpt) ~ keywordStr("]")).provided(printDebug && tree.typeOpt.exists)
         keywordStr("$") ~ spliceTypeText ~ {
           if args.isEmpty then keywordStr("{") ~ inPattern(toText(pattern)) ~ keywordStr("}")
-          else toText(pattern.symbol.name) ~ "(" ~ toTextGlobal(args, ", ") ~ ")"
+          else toText(pattern) ~ "(" ~ toTextGlobal(args, ", ") ~ ")"
         }
       case Hole(isTerm, idx, args, content) =>
         val (prefix, postfix) = if isTerm then ("{{{", "}}}") else ("[[[", "]]]")

docs/_docs/reference/metaprogramming/macros.md

@@ -452,10 +452,10 @@ The lambda arguments will replace the variables that might have been extruded.
 
 ```scala
 '{ ((x: Int) => x + 1).apply(2) } match
-  case '{ ((y: Int) => $f(y)).apply($z: Int) } =>
+  case '{ ((y: Int) => $f(y): Int).apply($z: Int) } =>
     // f may contain references to `x` (replaced by `$y`)
-    // f = (y: Expr[Int]) => '{ $y + 1 }
-    f(z) // generates '{ 2 + 1 }
+    // f = '{ (y: Int) => $y + 1 }
+    Expr.betaReduce('{ $f($z)}) // generates '{ 2 + 1 }
 ```
 
 

tests/neg-macros/i19342.check

@@ -0,0 +1,6 @@
+-- Error: tests/neg-macros/i19342.scala:5:26 ---------------------------------------------------------------------------
+5 |    case '{ ((y: Int) => $f(y)).apply($z: Int) } => () // error
+  |                          ^
+  |                          Type must be fully defined.
+  |                          Consider annotating the splice using a type ascription:
+  |                            ($f(y): XYZ).

tests/neg-macros/i19342.scala

@@ -0,0 +1,7 @@
+import scala.quoted.*
+
+def scrutinizeHoas(expr: Expr[Int])(using Quotes): Unit =
+  expr match {
+    case '{ ((y: Int) => $f(y)).apply($z: Int) } => () // error
+    case _ => ()
+  }