From dd3b668b8b9065fc9dd23f0c9df0631b6fd43d64 Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Sat, 23 Nov 2024 19:55:45 +0100
Subject: [PATCH] Discard the full annotation tree if a sub-tree is invalid

---
 .../src/dotty/tools/dotc/typer/Checking.scala | 74 +++++++++----------
 tests/neg/annot-invalid.check                 |  8 +-
 2 files changed, 40 insertions(+), 42 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/typer/Checking.scala b/compiler/src/dotty/tools/dotc/typer/Checking.scala
index 85ed864715e6..a6cd5f46eea7 100644
--- a/compiler/src/dotty/tools/dotc/typer/Checking.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Checking.scala
@@ -1425,48 +1425,46 @@ trait Checking {
             report.error(em"@${cls.name} needs a string literal as argument", arg.srcPos)
         tree
       case _ =>
-        checkAnnotTreeMap.transform(tree)
-
-  private def checkAnnotTreeMap(using Context) =
-    new TreeMap:
-      override def transform(tree: Tree)(using Context): Tree =
-        tree match
-          case _ if tree.isType =>
-            super.transform(tree)
-          case _: ( EmptyTree.type
-                  | Ident
-                  | Select
-                  | This
-                  | Super
-                  | Apply
-                  | TypeApply
-                  | Literal
-                  | New
-                  | Typed
-                  | NamedArg
-                  | Assign
-                  | Block
-                  | If
-                  | Closure
-                  | Return
-                  | SeqLiteral
-                  | Inlined
-                  | Quote
-                  | Splice
-                  | Hole
-                  | ValDef
-                  | DefDef
-                  | Annotated) =>
-            super.transform(tree)
-          case _ =>
+        tree.find(!isValidAnnotSubtree(_)) match
+          case None => tree
+          case Some(invalidSubTree) =>
             errorTree(
               EmptyTree,
-              em"""Implementation restriction: this tree cannot be used in an annotation.
-                  |Tree: ${tree}
-                  |Type: ${tree.tpe}""",
-              tree.srcPos
+              em"""Implementation restriction: expression cannot be used inside an annotation argument.
+                  |Tree: ${invalidSubTree}
+                  |Type: ${invalidSubTree.tpe}""",
+              invalidSubTree.srcPos
             )
 
+  /** Returns `true` if this tree can appear inside an annotation argument. */
+  private def isValidAnnotSubtree(subTree: Tree) =
+    subTree.isType || subTree.isInstanceOf[
+        EmptyTree.type
+      | Ident
+      | Select
+      | This
+      | Super
+      | Apply
+      | TypeApply
+      | Literal
+      | New
+      | Typed
+      | NamedArg
+      | Assign
+      | Block
+      | If
+      | Closure
+      | Return
+      | SeqLiteral
+      | Inlined
+      | Quote
+      | Splice
+      | Hole
+      | ValDef
+      | DefDef
+      | Annotated
+    ]
+
   /** 1. Check that all case classes that extend `scala.reflect.Enum` are `enum` cases
    *  2. Check that parameterised `enum` cases do not extend java.lang.Enum.
    *  3. Check that only a static `enum` base class can extend java.lang.Enum.
diff --git a/tests/neg/annot-invalid.check b/tests/neg/annot-invalid.check
index 09a29f1be6cb..8305f47a8c58 100644
--- a/tests/neg/annot-invalid.check
+++ b/tests/neg/annot-invalid.check
@@ -1,24 +1,24 @@
 -- Error: tests/neg/annot-invalid.scala:4:21 ---------------------------------------------------------------------------
 4 |  val x1: Int @annot(new Object {}) = 0 // error
   |                     ^^^^^^^^^^^^^
-  |                     Implementation restriction: this tree cannot be used in an annotation.
+  |                     Implementation restriction: expression cannot be used inside an annotation argument.
   |                     Tree: final class $anon() extends Object() {}
   |                     Type: Object {...}
 -- Error: tests/neg/annot-invalid.scala:5:28 ---------------------------------------------------------------------------
 5 |  val x2: Int @annot({class C}) = 0 // error
   |                      ^^^^^^^
-  |                      Implementation restriction: this tree cannot be used in an annotation.
+  |                      Implementation restriction: expression cannot be used inside an annotation argument.
   |                      Tree: class C() extends Object() {}
   |                      Type: C
 -- Error: tests/neg/annot-invalid.scala:7:9 ----------------------------------------------------------------------------
 7 |  @annot(new Object {}) val y1: Int = 0 // error
   |         ^^^^^^^^^^^^^
-  |         Implementation restriction: this tree cannot be used in an annotation.
+  |         Implementation restriction: expression cannot be used inside an annotation argument.
   |         Tree: final class $anon() extends Object() {}
   |         Type: Object {...}
 -- Error: tests/neg/annot-invalid.scala:8:16 ---------------------------------------------------------------------------
 8 |  @annot({class C}) val y2: Int = 0  // error
   |          ^^^^^^^
-  |          Implementation restriction: this tree cannot be used in an annotation.
+  |          Implementation restriction: expression cannot be used inside an annotation argument.
   |          Tree: class C() extends Object() {}
   |          Type: C