From c050bfbf6f1c932ae955a81a0571a0fa354442fc Mon Sep 17 00:00:00 2001
From: Jonathan Brouwer <jonathantbrouwer@gmail.com>
Date: Wed, 8 Oct 2025 10:10:20 +0200
Subject: [PATCH] Fix double error for `#[no_mangle]` on consts

---
 .../src/attributes/codegen_attrs.rs             |  2 ++
 .../rustc_attr_parsing/src/target_checking.rs   | 17 +++++++++++++++--
 tests/ui/issues/issue-45562.fixed               |  2 ++
 tests/ui/issues/issue-45562.rs                  |  2 ++
 tests/ui/issues/issue-45562.stderr              |  2 +-
 5 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
index 0f92968385f6..f09b02251e4d 100644
--- a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
@@ -6,6 +6,7 @@ use crate::session_diagnostics::{
     NakedFunctionIncompatibleAttribute, NullOnExport, NullOnObjcClass, NullOnObjcSelector,
     ObjcClassExpectedStringLiteral, ObjcSelectorExpectedStringLiteral,
 };
+use crate::target_checking::Policy::AllowSilent;
 
 pub(crate) struct OptimizeParser;
 
@@ -362,6 +363,7 @@ impl<S: Stage> NoArgsAttributeParser<S> for NoMangleParser {
         Allow(Target::Static),
         Allow(Target::Method(MethodKind::Inherent)),
         Allow(Target::Method(MethodKind::TraitImpl)),
+        AllowSilent(Target::Const), // Handled in the `InvalidNoMangleItems` pass
         Error(Target::Closure),
     ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::NoMangle;
diff --git a/compiler/rustc_attr_parsing/src/target_checking.rs b/compiler/rustc_attr_parsing/src/target_checking.rs
index d28f43943ba8..fabd364d3d7f 100644
--- a/compiler/rustc_attr_parsing/src/target_checking.rs
+++ b/compiler/rustc_attr_parsing/src/target_checking.rs
@@ -31,7 +31,9 @@ impl AllowedTargets {
     pub(crate) fn is_allowed(&self, target: Target) -> AllowedResult {
         match self {
             AllowedTargets::AllowList(list) => {
-                if list.contains(&Policy::Allow(target)) {
+                if list.contains(&Policy::Allow(target))
+                    || list.contains(&Policy::AllowSilent(target))
+                {
                     AllowedResult::Allowed
                 } else if list.contains(&Policy::Warn(target)) {
                     AllowedResult::Warn
@@ -40,7 +42,9 @@ impl AllowedTargets {
                 }
             }
             AllowedTargets::AllowListWarnRest(list) => {
-                if list.contains(&Policy::Allow(target)) {
+                if list.contains(&Policy::Allow(target))
+                    || list.contains(&Policy::AllowSilent(target))
+                {
                     AllowedResult::Allowed
                 } else if list.contains(&Policy::Error(target)) {
                     AllowedResult::Error
@@ -61,6 +65,7 @@ impl AllowedTargets {
         .iter()
         .filter_map(|target| match target {
             Policy::Allow(target) => Some(*target),
+            Policy::AllowSilent(_) => None, // Not listed in possible targets
             Policy::Warn(_) => None,
             Policy::Error(_) => None,
         })
@@ -68,10 +73,18 @@ impl AllowedTargets {
     }
 }
 
+/// This policy determines what diagnostics should be emitted based on the `Target` of the attribute.
 #[derive(Debug, Eq, PartialEq)]
 pub(crate) enum Policy {
+    /// A target that is allowed.
     Allow(Target),
+    /// A target that is allowed and not listed in the possible targets.
+    /// This is useful if the target is checked elsewhere.
+    AllowSilent(Target),
+    /// Emits a FCW on this target.
+    /// This is useful if the target was previously allowed but should not be.
     Warn(Target),
+    /// Emits an error on this target.
     Error(Target),
 }
 
diff --git a/tests/ui/issues/issue-45562.fixed b/tests/ui/issues/issue-45562.fixed
index 8dcdd3a541ce..529b5bd744e0 100644
--- a/tests/ui/issues/issue-45562.fixed
+++ b/tests/ui/issues/issue-45562.fixed
@@ -1,5 +1,7 @@
 //@ run-rustfix
 
+#![deny(unused_attributes)]
+
 #[no_mangle] pub static RAH: usize = 5;
 //~^ ERROR const items should never be `#[no_mangle]`
 
diff --git a/tests/ui/issues/issue-45562.rs b/tests/ui/issues/issue-45562.rs
index 08f6c8046dce..7c30a967c784 100644
--- a/tests/ui/issues/issue-45562.rs
+++ b/tests/ui/issues/issue-45562.rs
@@ -1,5 +1,7 @@
 //@ run-rustfix
 
+#![deny(unused_attributes)]
+
 #[no_mangle] pub const RAH: usize = 5;
 //~^ ERROR const items should never be `#[no_mangle]`
 
diff --git a/tests/ui/issues/issue-45562.stderr b/tests/ui/issues/issue-45562.stderr
index 6fae86f9f31c..55d35f76a019 100644
--- a/tests/ui/issues/issue-45562.stderr
+++ b/tests/ui/issues/issue-45562.stderr
@@ -1,5 +1,5 @@
 error: const items should never be `#[no_mangle]`
-  --> $DIR/issue-45562.rs:3:14
+  --> $DIR/issue-45562.rs:5:14
    |
 LL | #[no_mangle] pub const RAH: usize = 5;
    |              ---------^^^^^^^^^^^^^^^^