Rollup merge of #154585 - HerrCai0907:fix/no_mangle_generic_items, r=oli-obk

treat no_mangle_generic_items as hard error instead of lint warning

Reference PR:

- rust-lang/reference#1904

In rust-lang#4929 (comment), rustc should reject the no_mangled generic function.
This PR treat is as a hard error

Author: JonathanBrouwer

src/helpers.rs

@@ -132,15 +132,7 @@ pub fn iter_exported_symbols<'tcx>(
         if !(used || codegen_attrs.contains_extern_indicator()) {
             continue;
         }
-        // FIXME: `#[no_mangle]` makes no sense on a generic item, but still causes it to be
-        // considered "extern". Remove this once `no_mangle_generic_items` is a hard error.
-        let mono = {
-            let generics = tcx.generics_of(def_id);
-            !generics.requires_monomorphization(tcx)
-        };
-        if mono {
-            f(LOCAL_CRATE, def_id.into(), used)?;
-        }
+        f(LOCAL_CRATE, def_id.into(), used)?;
     }
 
     // Next, all our dependencies.

test-cargo-miri/issue-rust-86261/src/lib.rs

@@ -1,4 +1,4 @@
-#![allow(unused_imports, unused_attributes, no_mangle_generic_items)]
+#![allow(unused_imports, unused_attributes)]
 
 // Regression test for https://github.com/rust-lang/rust/issues/86261:
 // `#[no_mangle]` on a `use` item.
@@ -14,10 +14,6 @@ pub struct NoMangleStruct;
 #[export_name = "NoMangleStruct"]
 fn no_mangle_struct() {}
 
-// `#[no_mangle]` on a generic function can also cause ICEs.
-#[no_mangle]
-fn no_mangle_generic<T>() {}
-
-// Same as `no_mangle_struct()` but for the `no_mangle_generic()` generic function.
-#[export_name = "no_mangle_generic"]
-fn no_mangle_generic2() {}
+// Same as `no_mangle_struct()` but for the `no_mangle_struct()` function.
+#[export_name = "no_mangle_struct"]
+fn no_mangle_alias() {}

test-cargo-miri/src/main.rs

@@ -87,13 +87,13 @@ mod test {
                 fn assoc_fn_as_exported_symbol() -> i32;
                 fn make_true() -> bool;
                 fn NoMangleStruct();
-                fn no_mangle_generic();
+                fn no_mangle_struct();
             }
             assert_eq!(unsafe { exported_symbol() }, 123456);
             assert_eq!(unsafe { assoc_fn_as_exported_symbol() }, -123456);
             assert!(unsafe { make_true() });
             unsafe { NoMangleStruct() }
-            unsafe { no_mangle_generic() }
+            unsafe { no_mangle_struct() }
         }
     }