From d95e7a78d2bb5df8639b7f0ee804e013583bd602 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Tue, 24 Oct 2023 16:38:08 +0200
Subject: [PATCH] Add hint for nested quotes missing staged `Quotes`

Fix #17338
---
 .../src/dotty/tools/dotc/staging/CrossStageSafety.scala  | 4 ++++
 tests/neg-macros/i17338.check                            | 9 +++++++++
 tests/neg-macros/i17338.scala                            | 4 ++++
 3 files changed, 17 insertions(+)
 create mode 100644 tests/neg-macros/i17338.check
 create mode 100644 tests/neg-macros/i17338.scala

diff --git a/compiler/src/dotty/tools/dotc/staging/CrossStageSafety.scala b/compiler/src/dotty/tools/dotc/staging/CrossStageSafety.scala
index 25887cedb3e5..89d8f9a80ee3 100644
--- a/compiler/src/dotty/tools/dotc/staging/CrossStageSafety.scala
+++ b/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:
diff --git a/tests/neg-macros/i17338.check b/tests/neg-macros/i17338.check
new file mode 100644
index 000000000000..e47312130b1e
--- /dev/null
+++ b/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]]`.
diff --git a/tests/neg-macros/i17338.scala b/tests/neg-macros/i17338.scala
new file mode 100644
index 000000000000..941cbdd6216d
--- /dev/null
+++ b/tests/neg-macros/i17338.scala
@@ -0,0 +1,4 @@
+import scala.quoted.*
+
+def test(using quotes: Quotes): Expr[Expr[Int]] =
+  '{ '{ 1 } } // error