the #[track_caller] shim should not inherit #[no_mangle]

Author: folkertdev

compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

@@ -13,6 +13,8 @@ impl<'tcx> TyCtxt<'tcx> {
         self,
         instance_kind: InstanceKind<'_>,
     ) -> Cow<'tcx, CodegenFnAttrs> {
+        // NOTE: we try to not clone the `CodegenFnAttrs` when that is not needed.
+        // The `to_mut` method used below clones the inner value.
         let mut attrs = Cow::Borrowed(self.codegen_fn_attrs(instance_kind.def_id()));
 
         // Drop the `#[naked]` attribute on non-item `InstanceKind`s, like the shims that
@@ -23,6 +25,28 @@ impl<'tcx> TyCtxt<'tcx> {
             }
         }
 
+        // A shim created by `#[track_caller]` should not inherit any attributes
+        // that modify the symbol name. Failing to remove these attributes from
+        // the shim leads to errors like `symbol `foo` is already defined`.
+        //
+        // A `ClosureOnceShim` with the track_caller attribute does not have a symbol,
+        // and therefore can be skipped here.
+        if let InstanceKind::ReifyShim(_, _) = instance_kind
+            && attrs.flags.contains(CodegenFnAttrFlags::TRACK_CALLER)
+        {
+            if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
+                attrs.to_mut().flags.remove(CodegenFnAttrFlags::NO_MANGLE);
+            }
+
+            if attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
+                attrs.to_mut().flags.remove(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
+            }
+
+            if attrs.symbol_name.is_some() {
+                attrs.to_mut().symbol_name = None;
+            }
+        }
+
         attrs
     }
 }

tests/ui/rfcs/rfc-2091-track-caller/shim-does-not-modify-symbol.rs

@@ -0,0 +1,26 @@
+//@ run-pass
+#![feature(rustc_attrs)]
+
+// The shim that is generated for a function annotated with `#[track_caller]` should not inherit
+// attributes that modify its symbol name. Failing to remove these attributes from the shim
+// leads to errors like `symbol `foo` is already defined`.
+//
+// See also https://github.com/rust-lang/rust/issues/143162.
+
+#[unsafe(no_mangle)]
+#[track_caller]
+pub fn foo() {}
+
+#[unsafe(export_name = "bar")]
+#[track_caller]
+pub fn bar() {}
+
+#[rustc_std_internal_symbol]
+#[track_caller]
+pub fn baz() {}
+
+fn main() {
+    let _a = foo as fn();
+    let _b = bar as fn();
+    let _c = baz as fn();
+}