Fix double error for #[no_mangle] on consts

Author: JonathanBrouwer

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;

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
@@ -61,17 +65,26 @@ 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,
         })
         .collect()
     }
 }
 
+/// 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),
 }
 

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]`
 

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]`
 

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;
    |              ---------^^^^^^^^^^^^^^^^