Fix double warnings on #[no_mangle]

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 +363,8 @@ 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),
 }
 

compiler/rustc_codegen_ssa/messages.ftl

@@ -223,8 +223,6 @@ codegen_ssa_multiple_main_functions = entry symbol `main` declared multiple time
 
 codegen_ssa_no_field = no field `{$name}`
 
-codegen_ssa_no_mangle_nameless = `#[no_mangle]` cannot be used on {$definition} as it has no name
-
 codegen_ssa_no_module_named =
     no module named `{$user_path}` (mangled: {$cgu_name}). available modules: {$cgu_names}
 

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -19,7 +19,6 @@ use rustc_span::{Ident, Span, sym};
 use rustc_target::spec::SanitizerSet;
 
 use crate::errors;
-use crate::errors::NoMangleNameless;
 use crate::target_features::{
     check_target_feature_trait_unsafe, check_tied_features, from_target_feature_attr,
 };
@@ -182,14 +181,10 @@ fn process_builtin_attrs(
                     if tcx.opt_item_name(did.to_def_id()).is_some() {
                         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
                     } else {
-                        tcx.dcx().emit_err(NoMangleNameless {
-                            span: *attr_span,
-                            definition: format!(
-                                "{} {}",
-                                tcx.def_descr_article(did.to_def_id()),
-                                tcx.def_descr(did.to_def_id())
-                            ),
-                        });
+                        tcx.dcx().span_delayed_bug(
+                            *attr_span,
+                            "no_mangle should be on a named function",
+                        );
                     }
                 }
                 AttributeKind::Optimize(optimize, _) => codegen_fn_attrs.optimize = *optimize,

compiler/rustc_codegen_ssa/src/errors.rs

@@ -1284,14 +1284,6 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for TargetFeatureDisableOrEnable<'_
     }
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_no_mangle_nameless)]
-pub(crate) struct NoMangleNameless {
-    #[primary_span]
-    pub span: Span,
-    pub definition: String,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_feature_not_valid)]
 pub(crate) struct FeatureNotValid<'a> {

tests/ui/attributes/no-mangle-closure.rs

@@ -7,5 +7,5 @@ pub struct S([usize; 8]);
 
 pub fn outer_function(x: S, y: S) -> usize {
     (#[no_mangle] || y.0[0])()
-    //~^ ERROR `#[no_mangle]` cannot be used on a closure as it has no name
+    //~^ ERROR `#[no_mangle]` attribute cannot be used on closures
 }

tests/ui/attributes/no-mangle-closure.stderr

@@ -1,8 +1,10 @@
-error: `#[no_mangle]` cannot be used on a closure as it has no name
+error: `#[no_mangle]` attribute cannot be used on closures
   --> $DIR/no-mangle-closure.rs:9:6
    |
 LL |     (#[no_mangle] || y.0[0])()
    |      ^^^^^^^^^^^^
+   |
+   = help: `#[no_mangle]` can be applied to methods, functions, and statics
 
 error: aborting due to 1 previous error
 

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