Add hint for nested quotes missing staged Quotes (#18755)

Fix #17338

Author: nicolasstucki

compiler/src/dotty/tools/dotc/staging/CrossStageSafety.scala

@@ -228,6 +228,10 @@ class CrossStageSafety extends TreeMapWithStages {
         "\n\n" +
         "Hint: Staged references to inline definition in quotes are only inlined after the quote is spliced into level 0 code by a macro. " +
         "Try moving this inline definition in a statically accessible location such as an object (this definition can be private)."
+      else if level > 0 && sym.info.derivesFrom(defn.QuotesClass) then
+        s"""\n
+         |Hint: Nested quote needs a local context defined at level $level.
+         |One way to introduce this context is to give the outer quote the type `Expr[Quotes ?=> Expr[T]]`.""".stripMargin
       else ""
     report.error(
       em"""access to $symStr from wrong staging level:

tests/neg-macros/i17338.check

@@ -0,0 +1,9 @@
+-- Error: tests/neg-macros/i17338.scala:4:5 ----------------------------------------------------------------------------
+4 |  '{ '{ 1 } } // error
+  |     ^
+  |     access to parameter quotes from wrong staging level:
+  |      - the definition is at level 0,
+  |      - but the access is at level 1.
+  |
+  |     Hint: Nested quote needs a local context defined at level 1.
+  |     One way to introduce this context is to give the outer quote the type `Expr[Quotes ?=> Expr[T]]`.

tests/neg-macros/i17338.scala

@@ -0,0 +1,4 @@
+import scala.quoted.*
+
+def test(using quotes: Quotes): Expr[Expr[Int]] =
+  '{ '{ 1 } } // error