From f8eb853d0462ee31f7fda5401c72d4424778ce82 Mon Sep 17 00:00:00 2001
From: Hamza Remmal <hamza@remmal.net>
Date: Thu, 11 Sep 2025 18:59:11 +0200
Subject: [PATCH] fix: emit deprecation warnings when a symbol is annotated by
 a deprecated annotation

[Cherry-picked 8bd8f38d86bb5546ab61b3eb670704bef28dcd0f]
---
 .../tools/dotc/typer/CrossVersionChecks.scala   |  8 ++++++++
 tests/warn/i23905.check                         | 17 +++++++++++++++++
 tests/warn/i23905/Annot_1.scala                 |  2 ++
 tests/warn/i23905/Test_2.scala                  | 13 +++++++++++++
 4 files changed, 40 insertions(+)
 create mode 100644 tests/warn/i23905.check
 create mode 100644 tests/warn/i23905/Annot_1.scala
 create mode 100644 tests/warn/i23905/Test_2.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/CrossVersionChecks.scala b/compiler/src/dotty/tools/dotc/typer/CrossVersionChecks.scala
index 2122c10ad625..e4b0d7506319 100644
--- a/compiler/src/dotty/tools/dotc/typer/CrossVersionChecks.scala
+++ b/compiler/src/dotty/tools/dotc/typer/CrossVersionChecks.scala
@@ -37,6 +37,11 @@ class CrossVersionChecks extends MiniPhase:
       for annot <- sym.annotations if annot.symbol.isExperimental do
         Feature.checkExperimentalDef(annot.symbol, annot.tree)
 
+  private def checkDeprecatedAnnots(sym: Symbol)(using Context): Unit =
+    if sym.exists then
+      for annot <- sym.annotations if annot.symbol.isDeprecated do
+        checkDeprecatedRef(annot.symbol, annot.tree.srcPos)
+
   /** If @migration is present (indicating that the symbol has changed semantics between versions),
    *  emit a warning.
    */
@@ -85,16 +90,19 @@ class CrossVersionChecks extends MiniPhase:
   override def transformValDef(tree: ValDef)(using Context): ValDef =
     checkDeprecatedOvers(tree)
     checkExperimentalAnnots(tree.symbol)
+    checkDeprecatedAnnots(tree.symbol)
     tree
 
   override def transformDefDef(tree: DefDef)(using Context): DefDef =
     checkDeprecatedOvers(tree)
     checkExperimentalAnnots(tree.symbol)
+    checkDeprecatedAnnots(tree.symbol)
     tree
 
   override def transformTypeDef(tree: TypeDef)(using Context): TypeDef =
     // TODO do we need to check checkDeprecatedOvers(tree)?
     checkExperimentalAnnots(tree.symbol)
+    checkDeprecatedAnnots(tree.symbol)
     tree
 
   override def transformTemplate(tree: tpd.Template)(using Context): tpd.Tree =
diff --git a/tests/warn/i23905.check b/tests/warn/i23905.check
new file mode 100644
index 000000000000..9ca2ca0fb200
--- /dev/null
+++ b/tests/warn/i23905.check
@@ -0,0 +1,17 @@
+
+-- Deprecation Warning: tests/warn/i23905/Test_2.scala:3:0 -------------------------------------------------------------
+3 |@DeprecatedAnnotation // warn
+  |^^^^^^^^^^^^^^^^^^^^^
+  |class DeprecatedAnnotation is deprecated
+-- Deprecation Warning: tests/warn/i23905/Test_2.scala:6:0 -------------------------------------------------------------
+6 |@DeprecatedAnnotation // warn
+  |^^^^^^^^^^^^^^^^^^^^^
+  |class DeprecatedAnnotation is deprecated
+-- Deprecation Warning: tests/warn/i23905/Test_2.scala:9:0 -------------------------------------------------------------
+9 |@DeprecatedAnnotation // warn
+  |^^^^^^^^^^^^^^^^^^^^^
+  |class DeprecatedAnnotation is deprecated
+-- Deprecation Warning: tests/warn/i23905/Test_2.scala:12:0 ------------------------------------------------------------
+12 |@DeprecatedAnnotation // warn
+   |^^^^^^^^^^^^^^^^^^^^^
+   |class DeprecatedAnnotation is deprecated
diff --git a/tests/warn/i23905/Annot_1.scala b/tests/warn/i23905/Annot_1.scala
new file mode 100644
index 000000000000..e13664c67ebd
--- /dev/null
+++ b/tests/warn/i23905/Annot_1.scala
@@ -0,0 +1,2 @@
+@deprecated
+class DeprecatedAnnotation extends annotation.StaticAnnotation
diff --git a/tests/warn/i23905/Test_2.scala b/tests/warn/i23905/Test_2.scala
new file mode 100644
index 000000000000..248e923a5d83
--- /dev/null
+++ b/tests/warn/i23905/Test_2.scala
@@ -0,0 +1,13 @@
+//> using options -deprecation
+
+@DeprecatedAnnotation // warn
+object Test1
+
+@DeprecatedAnnotation // warn
+class Test2
+
+@DeprecatedAnnotation // warn
+def Test3 = ???
+
+@DeprecatedAnnotation // warn
+val Test4 = ???