Improve type test error message position

compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala

@@ -345,7 +345,7 @@ object TypeTestsCasts {
           val argType = tree.args.head.tpe
           val isTrusted = tree.hasAttachment(PatternMatcher.TrustedTypeTestKey)
           if (!isTrusted && !checkable(expr.tpe, argType, tree.span))
-            report.warning(i"the type test for $argType cannot be checked at runtime", tree.srcPos)
+            report.warning(i"the type test for $argType cannot be checked at runtime", expr.srcPos)
           transformTypeTest(expr, tree.args.head.tpe, flagUnrelated = true)
         }
         else if (sym.isTypeCast)

tests/neg-custom-args/fatal-warnings/i12253.check

@@ -0,0 +1,8 @@
+-- Error: tests/neg-custom-args/fatal-warnings/i12253.scala:11:10 ------------------------------------------------------
+11 |     case extractors.InlinedLambda(_, Select(_, name)) => Expr(name) // error // error
+   |          ^
+   |          the type test for extractors.q2.reflect.Term cannot be checked at runtime
+-- Error: tests/neg-custom-args/fatal-warnings/i12253.scala:11:38 ------------------------------------------------------
+11 |     case extractors.InlinedLambda(_, Select(_, name)) => Expr(name) // error // error
+   |                                      ^
+   |                                      the type test for q1.reflect.Select cannot be checked at runtime

tests/neg-custom-args/fatal-warnings/i12253.scala

@@ -0,0 +1,28 @@
+import scala.quoted.{given, *}
+import deriving.*,  compiletime.*
+
+object MacroUtils:
+  transparent inline def extractNameFromSelector[To, T](inline code: To => T) = ${extractNameFromSelectorImpl('code)}
+
+  def extractNameFromSelectorImpl[To: Type, T: Type](code: Expr[To => T])(using q1: Quotes): Expr[String] =
+    import quotes.reflect.*
+    val extractors = new Extractors
+    code.asTerm match
+     case extractors.InlinedLambda(_, Select(_, name)) => Expr(name) // error // error
+     case t => report.throwError(s"Illegal argument to extractor: ${code.show}, in tasty: $t")
+
+  class Extractors(using val q2: Quotes):
+    //attempt to strip away consecutive inlines in AST and extract only final lambda
+    import quotes.reflect.*
+
+    object InlinedLambda:
+      def unapply(arg: Term): Option[(List[ValDef], Term)] =
+        arg match
+          case Inlined(_, _, Lambda(vals, term)) => Some((vals, term))
+          case Inlined(_, _, nested) => InlinedLambda.unapply(nested)
+          case t => None
+    end InlinedLambda
+
+  end Extractors
+end MacroUtils
+