Keep tree of type ascriptions of quote pattern splices

These trees where removed as part of an optimization. However, they
should be kept around to allow for better error messages and IDE navigation.

The type of the ascription in pickled in the TASTy file but is elided in
the pickled quote pattern (same optimization already done later).

Fixes scala#18409

Author: nicolasstucki

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

@@ -259,14 +259,8 @@ trait QuotesAndSplices {
             pat.symbol.addAnnotation(Annotation(New(ref(defn.QuotedRuntimePatterns_fromAboveAnnot.typeRef)).withSpan(pat.span)))
           allTypeBindings += pat
           TypeTree(pat.symbol.typeRef).withSpan(pat.span)
-
-        case Typed(splice: SplicePattern, tpt) if !tpt.tpe.derivesFrom(defn.RepeatedParamClass) =>
-          // We drop the type ascription because it is redundant, the SplicePattern contains the same type
-          transform(tpt) // Collect type bindings
-          splice
         case _: SplicePattern =>
           tree
-
         case _ =>
           super.transform(tree)
     }

tests/neg-macros/i7264d.scala

@@ -1,7 +1,7 @@
 import scala.quoted.*
 class Foo {
   def f[T2: Type](e: Expr[T2])(using Quotes) = e match {
-    case '{ $x: *:[Int, Any] } => // error: Type argument Any does not conform to upper bound Tuple
+    case '{ $x: *:[Int, Any] } => // error // error: Type argument Any does not conform to upper bound Tuple
 
   }
 }

tests/neg-macros/quote-type-variable-no-inference-2.check

@@ -1,13 +1,19 @@
 -- Warning: tests/neg-macros/quote-type-variable-no-inference-2.scala:5:22 ---------------------------------------------
-5 |    case '{ $_ : F[t, t]; () } => // warn // error
+5 |    case '{ $_ : F[t, t]; () } => // warn // error // error
   |                      ^
   |                      Ignored bound <: Double
   |
   |                      Consider defining bounds explicitly:
   |                        '{ type t <: Int & Double; ... }
 -- [E057] Type Mismatch Error: tests/neg-macros/quote-type-variable-no-inference-2.scala:5:12 --------------------------
-5 |    case '{ $_ : F[t, t]; () } => // warn // error
+5 |    case '{ $_ : F[t, t]; () } => // warn // error // error
   |            ^
   |            Type argument t does not conform to upper bound Double in inferred type F[t, t]
   |
   | longer explanation available when compiling with `-explain`
+-- [E057] Type Mismatch Error: tests/neg-macros/quote-type-variable-no-inference-2.scala:5:20 --------------------------
+5 |    case '{ $_ : F[t, t]; () } => // warn // error // error
+  |                    ^
+  |                    Type argument t does not conform to upper bound Double
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg-macros/quote-type-variable-no-inference-2.scala

@@ -2,7 +2,7 @@ import scala.quoted.*
 
 def test2(x: Expr[Any])(using Quotes) =
   x match
-    case '{ $_ : F[t, t]; () } => // warn // error
+    case '{ $_ : F[t, t]; () } => // warn // error // error
     case '{ type u <: Int & Double; $_ : F[u, u] } =>
 
 type F[X <: Int, Y <: Double]

tests/neg-macros/quote-type-variable-no-inference-3.check

@@ -1,5 +1,5 @@
 -- Warning: tests/neg-macros/quote-type-variable-no-inference-3.scala:5:22 ---------------------------------------------
-5 |    case '{ $_ : F[t, t]; () } => // warn // error
+5 |    case '{ $_ : F[t, t]; () } => // warn // error // error
   |                      ^
   |                      Ignored bound <: Comparable[U]
   |
@@ -13,8 +13,14 @@
   |                                                 Consider defining bounds explicitly:
   |                                                   '{ type u <: Comparable[u] & Comparable[Any]; ... }
 -- [E057] Type Mismatch Error: tests/neg-macros/quote-type-variable-no-inference-3.scala:5:12 --------------------------
-5 |    case '{ $_ : F[t, t]; () } => // warn // error
+5 |    case '{ $_ : F[t, t]; () } => // warn // error // error
   |            ^
   |            Type argument t does not conform to upper bound Comparable[t] in inferred type F[t, t]
   |
   | longer explanation available when compiling with `-explain`
+-- [E057] Type Mismatch Error: tests/neg-macros/quote-type-variable-no-inference-3.scala:5:20 --------------------------
+5 |    case '{ $_ : F[t, t]; () } => // warn // error // error
+  |                    ^
+  |                    Type argument t does not conform to upper bound Comparable[t]
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg-macros/quote-type-variable-no-inference-3.scala

@@ -2,7 +2,7 @@ import scala.quoted.*
 
 def test2(x: Expr[Any])(using Quotes) =
   x match
-    case '{ $_ : F[t, t]; () } => // warn // error
+    case '{ $_ : F[t, t]; () } => // warn // error // error
     case '{ type u <: Comparable[`u`]; $_ : F[u, u] } =>
 
 type F[T, U <: Comparable[U]]

tests/pos-macros/i18409.scala

@@ -0,0 +1,26 @@
+// scalac: -Werror -Wunused:all
+
+import scala.quoted.*
+
+object model {
+  trait Transformer[Source, Dest] {
+    def transform(from: Source): Dest
+  }
+  object Transformer {
+    trait ForProduct[A, B] extends Transformer[A, B]
+  }
+}
+
+object Ops {
+  import model.Transformer // unused import false-positive
+
+  def unapply(using Quotes)(term: quotes.reflect.Term): Option[String] = {
+    term.asExpr match {
+      case '{
+            ($transformer: Transformer.ForProduct[a, b]).transform($appliedTo)
+          } =>
+        Some("")
+      case other => None
+    }
+  }
+}