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treat no_mangle_generic_items as hard error instead of lint warning #154585

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treat no_mangle_generic_items as hard error instead of lint warning #154585

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3b4b402
set no_mangle_generic_items deny by default
HerrCai0907 Mar 30, 2026
40a9cfe
fix review
HerrCai0907 Mar 30, 2026
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51 changes: 10 additions & 41 deletions compiler/rustc_lint/src/builtin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,11 +53,11 @@ 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, Level, LintContext};
declare_lint! {
Expand Down Expand Up @@ -924,36 +924,7 @@ 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(
Expand All @@ -964,11 +935,10 @@ 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::errors::BuiltinNoMangleGeneric {
span: cx.tcx.def_span(def_id),
suggestion: attr_span,
});
}
}
}
Expand Down Expand Up @@ -1607,7 +1577,6 @@ declare_lint_pass!(
ANONYMOUS_PARAMETERS,
UNUSED_DOC_COMMENTS,
NO_MANGLE_CONST_ITEMS,
NO_MANGLE_GENERIC_ITEMS,
MUTABLE_TRANSMUTES,
UNSTABLE_FEATURES,
UNREACHABLE_PUB,
Expand Down
16 changes: 16 additions & 0 deletions compiler/rustc_lint/src/errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Expand Down
5 changes: 5 additions & 0 deletions compiler/rustc_lint/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -643,6 +643,11 @@ fn register_builtins(store: &mut LintStore) {
);
store.register_removed("wasm_c_abi", "the wasm C ABI has been fixed");
store.register_removed("soft_unstable", "the general soft-unstable mechanism has been removed");
store.register_removed(
"no_mangle_generic_items",
"converted into hard error, \
generic items must always be mangled",
);
}

fn register_internals(store: &mut LintStore) {
Expand Down
14 changes: 0 additions & 14 deletions compiler/rustc_lint/src/lints.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -264,20 +264,6 @@ 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 {
Expand Down
2 changes: 1 addition & 1 deletion src/tools/miri/test-cargo-miri/issue-rust-86261/src/lib.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
#![allow(unused_imports, unused_attributes, no_mangle_generic_items)]
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@RalfJung RalfJung Apr 10, 2026 •
edited by rustbot
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View changes since the review

This looks like we should keep allowing the lint here until this is a hard error.

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@RalfJung RalfJung Apr 10, 2026

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Oh, the PR title is outdated. It is a hard error now, I see. Please update the PR title and description.

#![allow(unused_imports, unused_attributes)]

// Regression test for https://github.com/rust-lang/rust/issues/86261:
// `#[no_mangle]` on a `use` item.
Expand Down
3 changes: 1 addition & 2 deletions tests/codegen-llvm/avr/avr-func-addrspace.rs
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Expand Up @@ -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)()
}
Expand All @@ -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.
Expand Down
3 changes: 0 additions & 3 deletions tests/ui/backtrace/auxiliary/line-tables-only-helper.rs
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Original file line number Diff line number Diff line change
@@ -1,16 +1,13 @@
//@ compile-flags: -Cstrip=none -Cdebuginfo=line-tables-only

#[no_mangle]
pub fn baz<F>(mut cb: F, data: u32) where F: FnMut(u32) {
cb(data);
}

#[no_mangle]
pub fn bar<F>(cb: F, data: u32) where F: FnMut(u32) {
baz(cb, data);
}

#[no_mangle]
pub fn foo<F>(cb: F, data: u32) where F: FnMut(u32) {
bar(cb, data);
}
Expand Down
6 changes: 3 additions & 3 deletions tests/ui/backtrace/line-tables-only.rs
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Expand Up @@ -46,8 +46,8 @@ fn main() {
// line tables?
#[cfg(not(all(target_pointer_width = "32", target_env = "msvc")))]
{
assert_contains(&backtrace, "foo", "line-tables-only-helper.rs", 5);
assert_contains(&backtrace, "foo", "line-tables-only-helper.rs", 6);
}
assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 10);
assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 5);
assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 11);
assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 6);
}
157 changes: 0 additions & 157 deletions tests/ui/generics/export-name-on-generics.fixed
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This file was deleted.

2 changes: 0 additions & 2 deletions tests/ui/generics/export-name-on-generics.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,4 @@
//@ run-rustfix
#![allow(dead_code, mismatched_lifetime_syntaxes)]
#![deny(no_mangle_generic_items)]

#[export_name = "foo"]
pub fn foo<T>() {} //~ ERROR functions generic over types or consts must be mangled
Expand Down
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