treat no_mangle_generic_items as hard error instead of lint warning

compiler/rustc_lint/src/builtin.rs

@@ -54,11 +54,11 @@ use crate::lints::{
     BuiltinExplicitOutlives, BuiltinExplicitOutlivesSuggestion, BuiltinFeatureIssueNote,
     BuiltinIncompleteFeatures, BuiltinIncompleteFeaturesHelp, BuiltinInternalFeatures,
     BuiltinKeywordIdents, BuiltinMissingCopyImpl, BuiltinMissingDebugImpl, BuiltinMissingDoc,
-    BuiltinMutablesTransmutes, BuiltinNoMangleGeneric, BuiltinNonShorthandFieldPatterns,
-    BuiltinSpecialModuleNameUsed, BuiltinTrivialBounds, BuiltinTypeAliasBounds,
-    BuiltinUngatedAsyncFnTrackCaller, BuiltinUnpermittedTypeInit, BuiltinUnpermittedTypeInitSub,
-    BuiltinUnreachablePub, BuiltinUnsafe, BuiltinUnstableFeatures, BuiltinUnusedDocComment,
-    BuiltinUnusedDocCommentSub, BuiltinWhileTrue, EqInternalMethodImplemented, InvalidAsmLabel,
+    BuiltinMutablesTransmutes, BuiltinNonShorthandFieldPatterns, BuiltinSpecialModuleNameUsed,
+    BuiltinTrivialBounds, BuiltinTypeAliasBounds, BuiltinUngatedAsyncFnTrackCaller,
+    BuiltinUnpermittedTypeInit, BuiltinUnpermittedTypeInitSub, BuiltinUnreachablePub,
+    BuiltinUnsafe, BuiltinUnstableFeatures, BuiltinUnusedDocComment, BuiltinUnusedDocCommentSub,
+    BuiltinWhileTrue, EqInternalMethodImplemented, InvalidAsmLabel,
 };
 use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
 
@@ -870,36 +870,7 @@ declare_lint! {
     "const items will not have their symbols exported"
 }
 
-declare_lint! {
-    /// The `no_mangle_generic_items` lint detects generic items that must be
-    /// mangled.
-    ///
-    /// ### Example
-    ///
-    /// ```rust
-    /// #[unsafe(no_mangle)]
-    /// fn foo<T>(t: T) {}
-    ///
-    /// #[unsafe(export_name = "bar")]
-    /// fn bar<T>(t: T) {}
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// A function with generics must have its symbol mangled to accommodate
-    /// the generic parameter. The [`no_mangle`] and [`export_name`] attributes
-    /// have no effect in this situation, and should be removed.
-    ///
-    /// [`no_mangle`]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
-    /// [`export_name`]: https://doc.rust-lang.org/reference/abi.html#the-export_name-attribute
-    NO_MANGLE_GENERIC_ITEMS,
-    Warn,
-    "generic items must be mangled"
-}
-
-declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
+declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS]);
 
 impl InvalidNoMangleItems {
     fn check_no_mangle_on_generic_fn(
@@ -910,11 +881,10 @@ impl InvalidNoMangleItems {
     ) {
         let generics = cx.tcx.generics_of(def_id);
         if generics.requires_monomorphization(cx.tcx) {
-            cx.emit_span_lint(
-                NO_MANGLE_GENERIC_ITEMS,
-                cx.tcx.def_span(def_id),
-                BuiltinNoMangleGeneric { suggestion: attr_span },
-            );
+            cx.tcx.dcx().emit_err(crate::diagnostics::BuiltinNoMangleGeneric {
+                span: cx.tcx.def_span(def_id),
+                suggestion: attr_span,
+            });
         }
     }
 }
@@ -1553,7 +1523,6 @@ pub mod soft {
             ANONYMOUS_PARAMETERS,
             UNUSED_DOC_COMMENTS,
             NO_MANGLE_CONST_ITEMS,
-            NO_MANGLE_GENERIC_ITEMS,
             MUTABLE_TRANSMUTES,
             UNSTABLE_FEATURES,
             UNREACHABLE_PUB,

compiler/rustc_lint/src/diagnostics.rs

@@ -74,6 +74,22 @@ pub(crate) struct UnknownToolInScopedLint {
     pub is_nightly_build: bool,
 }
 
+#[derive(Diagnostic)]
+#[diag("functions generic over types or consts must be mangled")]
+pub(crate) struct BuiltinNoMangleGeneric {
+    #[primary_span]
+    pub span: Span,
+    // Use of `#[no_mangle]` suggests FFI intent; correct
+    // fix may be to monomorphize source by hand
+    #[suggestion(
+        "remove this attribute",
+        style = "short",
+        code = "",
+        applicability = "maybe-incorrect"
+    )]
+    pub suggestion: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag("`...` range patterns are deprecated", code = E0783)]
 pub(crate) struct BuiltinEllipsisInclusiveRangePatterns {

compiler/rustc_lint/src/lib.rs

@@ -695,6 +695,11 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, \
          see <https://github.com/rust-lang/rust/issues/78586> for more information",
     );
+    store.register_removed(
+        "no_mangle_generic_items",
+        "converted into hard error, \
+         generic items must always be mangled",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {

compiler/rustc_lint/src/lints.rs

@@ -225,20 +225,6 @@ pub(crate) enum BuiltinUnusedDocCommentSub {
     BlockHelp,
 }
 
-#[derive(Diagnostic)]
-#[diag("functions generic over types or consts must be mangled")]
-pub(crate) struct BuiltinNoMangleGeneric {
-    // Use of `#[no_mangle]` suggests FFI intent; correct
-    // fix may be to monomorphize source by hand
-    #[suggestion(
-        "remove this attribute",
-        style = "short",
-        code = "",
-        applicability = "maybe-incorrect"
-    )]
-    pub suggestion: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag("const items should never be `#[no_mangle]`")]
 pub(crate) struct BuiltinConstNoMangle {

src/tools/miri/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.

src/tools/miri/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() {}

src/tools/miri/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() }
         }
     }
 

tests/codegen-llvm/avr/avr-func-addrspace.rs

@@ -30,7 +30,6 @@ fn arbitrary_black_box(ptr: &usize, _: &mut u32) -> Result<(), ()> {
 }
 
 #[inline(never)]
-#[no_mangle]
 fn call_through_fn_trait(a: &mut impl Fn<(), Output = ()>) {
     (*a)()
 }
@@ -49,7 +48,7 @@ pub extern "C" fn test() {
 
     // A call through the Fn trait must use address space 1.
     //
-    // CHECK: call{{.+}}addrspace(1) void @call_through_fn_trait({{.*}})
+    // CHECK: call{{.+}}addrspace(1) void @{{.*call_through_fn_trait.*}}({{.*}})
     call_through_fn_trait(&mut update_bar_value);
 
     // A call through a global variable must use address space 1.

tests/ui/backtrace/auxiliary/line-tables-only-helper.rs

@@ -1,16 +1,13 @@
 //@ compile-flags: -Cstrip=none -Cdebuginfo=line-tables-only
 
-#[no_mangle]
 pub fn backtrace_with_baz_in_it<F>(mut cb: F, data: u32) where F: FnMut(u32) {
     cb(data);
 }
 
-#[no_mangle]
 pub fn backtrace_with_bar_in_it<F>(cb: F, data: u32) where F: FnMut(u32) {
     backtrace_with_baz_in_it(cb, data);
 }
 
-#[no_mangle]
 pub fn backtrace_with_foo_in_it<F>(cb: F, data: u32) where F: FnMut(u32) {
     backtrace_with_bar_in_it(cb, data);
 }

tests/ui/backtrace/line-tables-only.rs

@@ -32,9 +32,7 @@ fn assert_contains(
     expected_line: u32,
 ) {
     // The formatted frames look like this:
-    // `{ fn: "backtrace_with_baz_in_it", file: ".../tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 5 }`
-    // or this:
-    // `{ fn: "line_tables_only_helper::backtrace_with_baz_in_it<line_tables_only_helper::capture_backtrace::closure_env$0>", file: "...\tests\ui\backtrace\auxiliary\line-tables-only-helper.rs", line: 5 },`
+    // `{ fn: "line_tables_only_helper::backtrace_with_baz_in_it::<line_tables_only_helper::capture_backtrace::{closure#0}>", file: ".../tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 4 },
     // Make sure we match the right part when searching for the function name and line number.
     let expected_line_str = format!("line: {expected_line} ");
     eprintln!("{:#?}", backtrace);
@@ -63,8 +61,8 @@ fn main() {
     // And with #143208 we also lost `bar` in the line tables.
     #[cfg(not(all(target_pointer_width = "32", target_env = "msvc")))]
     {
-        assert_contains(&backtrace, "backtrace_with_foo_in_it", "line-tables-only-helper.rs", 15);
-        assert_contains(&backtrace, "backtrace_with_bar_in_it", "line-tables-only-helper.rs", 10);
+        assert_contains(&backtrace, "backtrace_with_foo_in_it", "line-tables-only-helper.rs", 12);
+        assert_contains(&backtrace, "backtrace_with_bar_in_it", "line-tables-only-helper.rs", 8);
     }
-    assert_contains(&backtrace, "backtrace_with_baz_in_it", "line-tables-only-helper.rs", 5);
+    assert_contains(&backtrace, "backtrace_with_baz_in_it", "line-tables-only-helper.rs", 4);
 }