1 use crate::{LateContext, LateLintPass, LintContext};
3 use rustc_attr as attr;
4 use rustc_data_structures::fx::FxHashSet;
5 use rustc_errors::{fluent, Applicability, DiagnosticMessage};
7 use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
8 use rustc_macros::LintDiagnostic;
9 use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
10 use rustc_middle::ty::subst::SubstsRef;
11 use rustc_middle::ty::{self, AdtKind, DefIdTree, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable};
12 use rustc_span::source_map;
13 use rustc_span::symbol::sym;
14 use rustc_span::{Span, Symbol};
15 use rustc_target::abi::{Abi, Size, WrappingRange};
16 use rustc_target::abi::{Integer, TagEncoding, Variants};
17 use rustc_target::spec::abi::Abi as SpecAbi;
21 use std::ops::ControlFlow;
24 /// The `unused_comparisons` lint detects comparisons made useless by
25 /// limits of the types involved.
39 /// A useless comparison may indicate a mistake, and should be fixed or
43 "comparisons made useless by limits of the types involved"
47 /// The `overflowing_literals` lint detects literal out of range for its
52 /// ```rust,compile_fail
60 /// It is usually a mistake to use a literal that overflows the type where
61 /// it is used. Either use a literal that is within range, or change the
62 /// type to be within the range of the literal.
65 "literal out of range for its type"
69 /// The `variant_size_differences` lint detects enums with widely varying
74 /// ```rust,compile_fail
75 /// #![deny(variant_size_differences)]
86 /// It can be a mistake to add a variant to an enum that is much larger
87 /// than the other variants, bloating the overall size required for all
88 /// variants. This can impact performance and memory usage. This is
89 /// triggered if one variant is more than 3 times larger than the
90 /// second-largest variant.
92 /// Consider placing the large variant's contents on the heap (for example
93 /// via [`Box`]) to keep the overall size of the enum itself down.
95 /// This lint is "allow" by default because it can be noisy, and may not be
96 /// an actual problem. Decisions about this should be guided with
97 /// profiling and benchmarking.
99 /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html
100 VARIANT_SIZE_DIFFERENCES,
102 "detects enums with widely varying variant sizes"
105 #[derive(Copy, Clone)]
106 pub struct TypeLimits {
107 /// Id of the last visited negated expression
108 negated_expr_id: Option<hir::HirId>,
111 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
114 pub fn new() -> TypeLimits {
115 TypeLimits { negated_expr_id: None }
119 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint (`expr..MAX+1`).
120 /// Returns `true` iff the lint was emitted.
121 fn lint_overflowing_range_endpoint<'tcx>(
122 cx: &LateContext<'tcx>,
126 expr: &'tcx hir::Expr<'tcx>,
129 // We only want to handle exclusive (`..`) ranges,
130 // which are represented as `ExprKind::Struct`.
131 let par_id = cx.tcx.hir().get_parent_node(expr.hir_id);
132 let Node::ExprField(field) = cx.tcx.hir().get(par_id) else { return false };
133 let field_par_id = cx.tcx.hir().get_parent_node(field.hir_id);
134 let Node::Expr(struct_expr) = cx.tcx.hir().get(field_par_id) else { return false };
135 if !is_range_literal(struct_expr) {
138 let ExprKind::Struct(_, eps, _) = &struct_expr.kind else { return false };
143 // We can suggest using an inclusive range
144 // (`..=`) instead only if it is the `end` that is
145 // overflowing and only by 1.
146 if !(eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max) {
149 let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) else { return false };
152 OVERFLOWING_LITERALS,
154 fluent::lint_range_endpoint_out_of_range,
156 use ast::{LitIntType, LitKind};
158 lint.set_arg("ty", ty);
160 // We need to preserve the literal's suffix,
161 // as it may determine typing information.
162 let suffix = match lit.node {
163 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
164 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
165 LitKind::Int(_, LitIntType::Unsuffixed) => "",
168 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
169 lint.span_suggestion(
173 Applicability::MachineApplicable,
180 // We've just emitted a lint, special cased for `(...)..MAX+1` ranges,
181 // return `true` so the callers don't also emit a lint
185 // For `isize` & `usize`, be conservative with the warnings, so that the
186 // warnings are consistent between 32- and 64-bit platforms.
187 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
189 ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
190 ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
191 ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
192 ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
193 ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
194 ty::IntTy::I128 => (i128::MIN, i128::MAX),
198 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
199 let max = match uint_ty {
200 ty::UintTy::Usize => u64::MAX.into(),
201 ty::UintTy::U8 => u8::MAX.into(),
202 ty::UintTy::U16 => u16::MAX.into(),
203 ty::UintTy::U32 => u32::MAX.into(),
204 ty::UintTy::U64 => u64::MAX.into(),
205 ty::UintTy::U128 => u128::MAX,
210 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
211 let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
212 let firstch = src.chars().next()?;
215 match src.chars().nth(1) {
216 Some('x' | 'b') => return Some(src),
224 fn report_bin_hex_error(
225 cx: &LateContext<'_>,
226 expr: &hir::Expr<'_>,
234 OVERFLOWING_LITERALS,
236 fluent::lint_overflowing_bin_hex,
238 let (t, actually) = match ty {
239 attr::IntType::SignedInt(t) => {
240 let actually = if negative {
241 -(size.sign_extend(val) as i128)
243 size.sign_extend(val) as i128
245 (t.name_str(), actually.to_string())
247 attr::IntType::UnsignedInt(t) => {
248 let actually = size.truncate(val);
249 (t.name_str(), actually.to_string())
254 // If the value is negative,
255 // emits a note about the value itself, apart from the literal.
256 lint.note(fluent::negative_note);
257 lint.note(fluent::negative_becomes_note);
259 lint.note(fluent::positive_note);
261 if let Some(sugg_ty) =
262 get_type_suggestion(cx.typeck_results().node_type(expr.hir_id), val, negative)
264 lint.set_arg("suggestion_ty", sugg_ty);
265 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
266 let (sans_suffix, _) = repr_str.split_at(pos);
267 lint.span_suggestion(
270 format!("{}{}", sans_suffix, sugg_ty),
271 Applicability::MachineApplicable,
274 lint.help(fluent::help);
277 lint.set_arg("ty", t)
278 .set_arg("lit", repr_str)
280 .set_arg("actually", actually);
287 // This function finds the next fitting type and generates a suggestion string.
288 // It searches for fitting types in the following way (`X < Y`):
289 // - `iX`: if literal fits in `uX` => `uX`, else => `iY`
293 // No suggestion for: `isize`, `usize`.
294 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
297 macro_rules! find_fit {
298 ($ty:expr, $val:expr, $negative:expr,
299 $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
301 let _neg = if negative { 1 } else { 0 };
304 $(if !negative && val <= uint_ty_range($utypes).1 {
305 return Some($utypes.name_str())
307 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
308 return Some($itypes.name_str())
318 ty::Int(i) => find_fit!(i, val, negative,
319 I8 => [U8] => [I16, I32, I64, I128],
320 I16 => [U16] => [I32, I64, I128],
321 I32 => [U32] => [I64, I128],
322 I64 => [U64] => [I128],
323 I128 => [U128] => []),
324 ty::Uint(u) => find_fit!(u, val, negative,
325 U8 => [U8, U16, U32, U64, U128] => [],
326 U16 => [U16, U32, U64, U128] => [],
327 U32 => [U32, U64, U128] => [],
328 U64 => [U64, U128] => [],
329 U128 => [U128] => []),
334 fn lint_int_literal<'tcx>(
335 cx: &LateContext<'tcx>,
336 type_limits: &TypeLimits,
337 e: &'tcx hir::Expr<'tcx>,
342 let int_type = t.normalize(cx.sess().target.pointer_width);
343 let (min, max) = int_ty_range(int_type);
344 let max = max as u128;
345 let negative = type_limits.negated_expr_id == Some(e.hir_id);
347 // Detect literal value out of range [min, max] inclusive
348 // avoiding use of -min to prevent overflow/panic
349 if (negative && v > max + 1) || (!negative && v > max) {
350 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
351 report_bin_hex_error(
354 attr::IntType::SignedInt(ty::ast_int_ty(t)),
355 Integer::from_int_ty(cx, t).size(),
363 if lint_overflowing_range_endpoint(cx, lit, v, max, e, t.name_str()) {
364 // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
368 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, fluent::lint_overflowing_int, |lint| {
369 lint.set_arg("ty", t.name_str())
374 .span_to_snippet(lit.span)
375 .expect("must get snippet from literal"),
381 if let Some(sugg_ty) =
382 get_type_suggestion(cx.typeck_results().node_type(e.hir_id), v, negative)
384 lint.set_arg("suggestion_ty", sugg_ty);
385 lint.help(fluent::help);
393 fn lint_uint_literal<'tcx>(
394 cx: &LateContext<'tcx>,
395 e: &'tcx hir::Expr<'tcx>,
399 let uint_type = t.normalize(cx.sess().target.pointer_width);
400 let (min, max) = uint_ty_range(uint_type);
401 let lit_val: u128 = match lit.node {
402 // _v is u8, within range by definition
403 ast::LitKind::Byte(_v) => return,
404 ast::LitKind::Int(v, _) => v,
407 if lit_val < min || lit_val > max {
408 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
409 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
411 hir::ExprKind::Cast(..) => {
412 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
414 OVERFLOWING_LITERALS,
416 fluent::lint_only_cast_u8_to_char,
418 lint.span_suggestion(
421 format!("'\\u{{{:X}}}'", lit_val),
422 Applicability::MachineApplicable,
432 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, t.name_str()) {
433 // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
436 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
437 report_bin_hex_error(
440 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
441 Integer::from_uint_ty(cx, t).size(),
448 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, fluent::lint_overflowing_uint, |lint| {
449 lint.set_arg("ty", t.name_str())
454 .span_to_snippet(lit.span)
455 .expect("must get snippet from literal"),
464 fn lint_literal<'tcx>(
465 cx: &LateContext<'tcx>,
466 type_limits: &TypeLimits,
467 e: &'tcx hir::Expr<'tcx>,
470 match *cx.typeck_results().node_type(e.hir_id).kind() {
473 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
474 lint_int_literal(cx, type_limits, e, lit, t, v)
479 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
481 let is_infinite = match lit.node {
482 ast::LitKind::Float(v, _) => match t {
483 ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
484 ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
488 if is_infinite == Ok(true) {
490 OVERFLOWING_LITERALS,
492 fluent::lint_overflowing_literal,
494 lint.set_arg("ty", t.name_str())
499 .span_to_snippet(lit.span)
500 .expect("must get snippet from literal"),
511 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
512 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
514 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
515 // propagate negation, if the negation itself isn't negated
516 if self.negated_expr_id != Some(e.hir_id) {
517 self.negated_expr_id = Some(expr.hir_id);
520 hir::ExprKind::Binary(binop, ref l, ref r) => {
521 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
525 fluent::lint_unused_comparisons,
530 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
534 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
536 hir::BinOpKind::Lt => v > min && v <= max,
537 hir::BinOpKind::Le => v >= min && v < max,
538 hir::BinOpKind::Gt => v >= min && v < max,
539 hir::BinOpKind::Ge => v > min && v <= max,
540 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
545 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
549 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
550 hir::BinOpKind::Le => hir::BinOpKind::Ge,
551 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
552 hir::BinOpKind::Ge => hir::BinOpKind::Le,
559 cx: &LateContext<'_>,
564 let (lit, expr, swap) = match (&l.kind, &r.kind) {
565 (&hir::ExprKind::Lit(_), _) => (l, r, true),
566 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
569 // Normalize the binop so that the literal is always on the RHS in
571 let norm_binop = if swap { rev_binop(binop) } else { binop };
572 match *cx.typeck_results().node_type(expr.hir_id).kind() {
574 let (min, max) = int_ty_range(int_ty);
575 let lit_val: i128 = match lit.kind {
576 hir::ExprKind::Lit(ref li) => match li.node {
579 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
585 is_valid(norm_binop, lit_val, min, max)
587 ty::Uint(uint_ty) => {
588 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
589 let lit_val: u128 = match lit.kind {
590 hir::ExprKind::Lit(ref li) => match li.node {
591 ast::LitKind::Int(v, _) => v,
596 is_valid(norm_binop, lit_val, min, max)
602 fn is_comparison(binop: hir::BinOp) -> bool {
617 /// The `improper_ctypes` lint detects incorrect use of types in foreign
624 /// static STATIC: String;
632 /// The compiler has several checks to verify that types used in `extern`
633 /// blocks are safe and follow certain rules to ensure proper
634 /// compatibility with the foreign interfaces. This lint is issued when it
635 /// detects a probable mistake in a definition. The lint usually should
636 /// provide a description of the issue, along with possibly a hint on how
640 "proper use of libc types in foreign modules"
643 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
646 /// The `improper_ctypes_definitions` lint detects incorrect use of
647 /// [`extern` function] definitions.
649 /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
654 /// # #![allow(unused)]
655 /// pub extern "C" fn str_type(p: &str) { }
662 /// There are many parameter and return types that may be specified in an
663 /// `extern` function that are not compatible with the given ABI. This
664 /// lint is an alert that these types should not be used. The lint usually
665 /// should provide a description of the issue, along with possibly a hint
666 /// on how to resolve it.
667 IMPROPER_CTYPES_DEFINITIONS,
669 "proper use of libc types in foreign item definitions"
672 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
674 #[derive(Clone, Copy)]
675 pub(crate) enum CItemKind {
680 struct ImproperCTypesVisitor<'a, 'tcx> {
681 cx: &'a LateContext<'tcx>,
685 enum FfiResult<'tcx> {
687 FfiPhantom(Ty<'tcx>),
688 FfiUnsafe { ty: Ty<'tcx>, reason: DiagnosticMessage, help: Option<DiagnosticMessage> },
691 pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
693 def: ty::AdtDef<'tcx>,
695 tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
698 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
700 pub fn transparent_newtype_field<'a, 'tcx>(
702 variant: &'a ty::VariantDef,
703 ) -> Option<&'a ty::FieldDef> {
704 let param_env = tcx.param_env(variant.def_id);
705 variant.fields.iter().find(|field| {
706 let field_ty = tcx.type_of(field.did);
707 let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
712 /// Is type known to be non-null?
713 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
716 ty::FnPtr(_) => true,
718 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
719 ty::Adt(def, substs) if def.repr().transparent() && !def.is_union() => {
720 let marked_non_null = nonnull_optimization_guaranteed(tcx, *def);
726 // `UnsafeCell` has its niche hidden.
727 if def.is_unsafe_cell() {
733 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
734 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
740 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
741 /// If the type passed in was not scalar, returns None.
742 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
744 Some(match *ty.kind() {
745 ty::Adt(field_def, field_substs) => {
746 let inner_field_ty = {
747 let mut first_non_zst_ty = field_def
750 .filter_map(|v| transparent_newtype_field(cx.tcx, v));
752 first_non_zst_ty.clone().count(),
754 "Wrong number of fields for transparent type"
758 .expect("No non-zst fields in transparent type.")
759 .ty(tcx, field_substs)
761 return get_nullable_type(cx, inner_field_ty);
763 ty::Int(ty) => tcx.mk_mach_int(ty),
764 ty::Uint(ty) => tcx.mk_mach_uint(ty),
765 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
766 // As these types are always non-null, the nullable equivalent of
767 // Option<T> of these types are their raw pointer counterparts.
768 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
770 // There is no nullable equivalent for Rust's function pointers -- you
771 // must use an Option<fn(..) -> _> to represent it.
775 // We should only ever reach this case if ty_is_known_nonnull is extended
779 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
787 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
788 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
789 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
790 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
791 /// FIXME: This duplicates code in codegen.
792 pub(crate) fn repr_nullable_ptr<'tcx>(
793 cx: &LateContext<'tcx>,
796 ) -> Option<Ty<'tcx>> {
797 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
798 if let ty::Adt(ty_def, substs) = ty.kind() {
799 let field_ty = match &ty_def.variants().raw[..] {
800 [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
801 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
807 if !ty_is_known_nonnull(cx, field_ty, ckind) {
811 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
812 // If the computed size for the field and the enum are different, the nonnull optimization isn't
813 // being applied (and we've got a problem somewhere).
814 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
815 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
816 bug!("improper_ctypes: Option nonnull optimization not applied?");
819 // Return the nullable type this Option-like enum can be safely represented with.
820 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
821 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
822 match field_ty_scalar.valid_range(cx) {
823 WrappingRange { start: 0, end }
824 if end == field_ty_scalar.size(&cx.tcx).unsigned_int_max() - 1 =>
826 return Some(get_nullable_type(cx, field_ty).unwrap());
828 WrappingRange { start: 1, .. } => {
829 return Some(get_nullable_type(cx, field_ty).unwrap());
831 WrappingRange { start, end } => {
832 unreachable!("Unhandled start and end range: ({}, {})", start, end)
840 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
841 /// Check if the type is array and emit an unsafe type lint.
842 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
843 if let ty::Array(..) = ty.kind() {
844 self.emit_ffi_unsafe_type_lint(
847 fluent::lint_improper_ctypes_array_reason,
848 Some(fluent::lint_improper_ctypes_array_help),
856 /// Checks if the given field's type is "ffi-safe".
857 fn check_field_type_for_ffi(
859 cache: &mut FxHashSet<Ty<'tcx>>,
860 field: &ty::FieldDef,
861 substs: SubstsRef<'tcx>,
862 ) -> FfiResult<'tcx> {
863 let field_ty = field.ty(self.cx.tcx, substs);
864 if field_ty.has_opaque_types() {
865 self.check_type_for_ffi(cache, field_ty)
867 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
868 self.check_type_for_ffi(cache, field_ty)
872 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
873 fn check_variant_for_ffi(
875 cache: &mut FxHashSet<Ty<'tcx>>,
877 def: ty::AdtDef<'tcx>,
878 variant: &ty::VariantDef,
879 substs: SubstsRef<'tcx>,
880 ) -> FfiResult<'tcx> {
883 if def.repr().transparent() {
884 // Can assume that at most one field is not a ZST, so only check
885 // that field's type for FFI-safety.
886 if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
887 self.check_field_type_for_ffi(cache, field, substs)
889 // All fields are ZSTs; this means that the type should behave
890 // like (), which is FFI-unsafe
891 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_struct_zst, help: None }
894 // We can't completely trust repr(C) markings; make sure the fields are
896 let mut all_phantom = !variant.fields.is_empty();
897 for field in &variant.fields {
898 match self.check_field_type_for_ffi(cache, &field, substs) {
902 FfiPhantom(..) if def.is_enum() => {
905 reason: fluent::lint_improper_ctypes_enum_phantomdata,
914 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
918 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
919 /// representation which can be exported to C code).
920 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
923 let tcx = self.cx.tcx;
925 // Protect against infinite recursion, for example
926 // `struct S(*mut S);`.
927 // FIXME: A recursion limit is necessary as well, for irregular
929 if !cache.insert(ty) {
934 ty::Adt(def, substs) => {
935 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
936 if ty.boxed_ty().is_sized(tcx, self.cx.param_env) {
941 reason: fluent::lint_improper_ctypes_box,
946 if def.is_phantom_data() {
947 return FfiPhantom(ty);
949 match def.adt_kind() {
950 AdtKind::Struct | AdtKind::Union => {
951 if !def.repr().c() && !def.repr().transparent() {
954 reason: if def.is_struct() {
955 fluent::lint_improper_ctypes_struct_layout_reason
957 fluent::lint_improper_ctypes_union_layout_reason
959 help: if def.is_struct() {
960 Some(fluent::lint_improper_ctypes_struct_layout_help)
962 Some(fluent::lint_improper_ctypes_union_layout_help)
967 let is_non_exhaustive =
968 def.non_enum_variant().is_field_list_non_exhaustive();
969 if is_non_exhaustive && !def.did().is_local() {
972 reason: if def.is_struct() {
973 fluent::lint_improper_ctypes_struct_non_exhaustive
975 fluent::lint_improper_ctypes_union_non_exhaustive
981 if def.non_enum_variant().fields.is_empty() {
984 reason: if def.is_struct() {
985 fluent::lint_improper_ctypes_struct_fieldless_reason
987 fluent::lint_improper_ctypes_union_fieldless_reason
989 help: if def.is_struct() {
990 Some(fluent::lint_improper_ctypes_struct_fieldless_help)
992 Some(fluent::lint_improper_ctypes_union_fieldless_help)
997 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
1000 if def.variants().is_empty() {
1001 // Empty enums are okay... although sort of useless.
1005 // Check for a repr() attribute to specify the size of the
1007 if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
1009 // Special-case types like `Option<extern fn()>`.
1010 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
1013 reason: fluent::lint_improper_ctypes_enum_repr_reason,
1014 help: Some(fluent::lint_improper_ctypes_enum_repr_help),
1019 if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
1022 reason: fluent::lint_improper_ctypes_non_exhaustive,
1027 // Check the contained variants.
1028 for variant in def.variants() {
1029 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1030 if is_non_exhaustive && !variant.def_id.is_local() {
1033 reason: fluent::lint_improper_ctypes_non_exhaustive_variant,
1038 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1049 ty::Char => FfiUnsafe {
1051 reason: fluent::lint_improper_ctypes_char_reason,
1052 help: Some(fluent::lint_improper_ctypes_char_help),
1055 ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => {
1056 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_128bit, help: None }
1059 // Primitive types with a stable representation.
1060 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1062 ty::Slice(_) => FfiUnsafe {
1064 reason: fluent::lint_improper_ctypes_slice_reason,
1065 help: Some(fluent::lint_improper_ctypes_slice_help),
1068 ty::Dynamic(..) => {
1069 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_dyn, help: None }
1072 ty::Str => FfiUnsafe {
1074 reason: fluent::lint_improper_ctypes_str_reason,
1075 help: Some(fluent::lint_improper_ctypes_str_help),
1078 ty::Tuple(..) => FfiUnsafe {
1080 reason: fluent::lint_improper_ctypes_tuple_reason,
1081 help: Some(fluent::lint_improper_ctypes_tuple_help),
1084 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1086 matches!(self.mode, CItemKind::Definition)
1087 && ty.is_sized(self.cx.tcx, self.cx.param_env)
1093 ty::RawPtr(ty::TypeAndMut { ty, .. })
1094 if match ty.kind() {
1095 ty::Tuple(tuple) => tuple.is_empty(),
1102 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1103 self.check_type_for_ffi(cache, ty)
1106 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1109 if self.is_internal_abi(sig.abi()) {
1112 reason: fluent::lint_improper_ctypes_fnptr_reason,
1113 help: Some(fluent::lint_improper_ctypes_fnptr_help),
1117 let sig = tcx.erase_late_bound_regions(sig);
1118 if !sig.output().is_unit() {
1119 let r = self.check_type_for_ffi(cache, sig.output());
1127 for arg in sig.inputs() {
1128 let r = self.check_type_for_ffi(cache, *arg);
1139 ty::Foreign(..) => FfiSafe,
1141 // While opaque types are checked for earlier, if a projection in a struct field
1142 // normalizes to an opaque type, then it will reach this branch.
1144 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_opaque, help: None }
1147 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1148 // so they are currently ignored for the purposes of this lint.
1149 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1154 | ty::Projection(..)
1160 | ty::GeneratorWitness(..)
1161 | ty::Placeholder(..)
1162 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1166 fn emit_ffi_unsafe_type_lint(
1170 note: DiagnosticMessage,
1171 help: Option<DiagnosticMessage>,
1173 let lint = match self.mode {
1174 CItemKind::Declaration => IMPROPER_CTYPES,
1175 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1178 self.cx.struct_span_lint(lint, sp, fluent::lint_improper_ctypes, |lint| {
1179 let item_description = match self.mode {
1180 CItemKind::Declaration => "block",
1181 CItemKind::Definition => "fn",
1183 lint.set_arg("ty", ty);
1184 lint.set_arg("desc", item_description);
1185 lint.span_label(sp, fluent::label);
1186 if let Some(help) = help {
1190 if let ty::Adt(def, _) = ty.kind() {
1191 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did()) {
1192 lint.span_note(sp, fluent::note);
1199 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1200 struct ProhibitOpaqueTypes;
1201 impl<'tcx> ty::visit::TypeVisitor<'tcx> for ProhibitOpaqueTypes {
1202 type BreakTy = Ty<'tcx>;
1204 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1205 if !ty.has_opaque_types() {
1206 return ControlFlow::CONTINUE;
1209 if let ty::Opaque(..) = ty.kind() {
1210 ControlFlow::Break(ty)
1212 ty.super_visit_with(self)
1217 if let Some(ty) = self
1220 .normalize_erasing_regions(self.cx.param_env, ty)
1221 .visit_with(&mut ProhibitOpaqueTypes)
1224 self.emit_ffi_unsafe_type_lint(ty, sp, fluent::lint_improper_ctypes_opaque, None);
1231 fn check_type_for_ffi_and_report_errors(
1236 is_return_type: bool,
1238 // We have to check for opaque types before `normalize_erasing_regions`,
1239 // which will replace opaque types with their underlying concrete type.
1240 if self.check_for_opaque_ty(sp, ty) {
1241 // We've already emitted an error due to an opaque type.
1245 // it is only OK to use this function because extern fns cannot have
1246 // any generic types right now:
1247 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1249 // C doesn't really support passing arrays by value - the only way to pass an array by value
1250 // is through a struct. So, first test that the top level isn't an array, and then
1251 // recursively check the types inside.
1252 if !is_static && self.check_for_array_ty(sp, ty) {
1256 // Don't report FFI errors for unit return types. This check exists here, and not in
1257 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1259 if is_return_type && ty.is_unit() {
1263 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1264 FfiResult::FfiSafe => {}
1265 FfiResult::FfiPhantom(ty) => {
1266 self.emit_ffi_unsafe_type_lint(
1269 fluent::lint_improper_ctypes_only_phantomdata,
1273 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1274 // argument, which after substitution, is `()`, then this branch can be hit.
1275 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1276 FfiResult::FfiUnsafe { ty, reason, help } => {
1277 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
1282 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1283 let def_id = self.cx.tcx.hir().local_def_id(id);
1284 let sig = self.cx.tcx.fn_sig(def_id);
1285 let sig = self.cx.tcx.erase_late_bound_regions(sig);
1287 for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1288 self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
1291 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1292 let ret_ty = sig.output();
1293 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1297 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1298 let def_id = self.cx.tcx.hir().local_def_id(id);
1299 let ty = self.cx.tcx.type_of(def_id);
1300 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1303 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1306 SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1311 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1312 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1313 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1314 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1316 if !vis.is_internal_abi(abi) {
1318 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1319 vis.check_foreign_fn(it.hir_id(), decl);
1321 hir::ForeignItemKind::Static(ref ty, _) => {
1322 vis.check_foreign_static(it.hir_id(), ty.span);
1324 hir::ForeignItemKind::Type => (),
1330 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1333 cx: &LateContext<'tcx>,
1334 kind: hir::intravisit::FnKind<'tcx>,
1335 decl: &'tcx hir::FnDecl<'_>,
1336 _: &'tcx hir::Body<'_>,
1340 use hir::intravisit::FnKind;
1342 let abi = match kind {
1343 FnKind::ItemFn(_, _, header, ..) => header.abi,
1344 FnKind::Method(_, sig, ..) => sig.header.abi,
1348 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1349 if !vis.is_internal_abi(abi) {
1350 vis.check_foreign_fn(hir_id, decl);
1355 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1357 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1358 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1359 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1360 let t = cx.tcx.type_of(it.owner_id);
1361 let ty = cx.tcx.erase_regions(t);
1362 let Ok(layout) = cx.layout_of(ty) else { return };
1363 let Variants::Multiple {
1364 tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1365 } = &layout.variants else {
1369 let tag_size = tag.size(&cx.tcx).bytes();
1372 "enum `{}` is {} bytes large with layout:\n{:#?}",
1374 layout.size.bytes(),
1378 let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1379 .map(|(variant, variant_layout)| {
1380 // Subtract the size of the enum tag.
1381 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1383 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1387 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1390 } else if size > s {
1397 // We only warn if the largest variant is at least thrice as large as
1398 // the second-largest.
1399 if largest > slargest * 3 && slargest > 0 {
1400 cx.struct_span_lint(
1401 VARIANT_SIZE_DIFFERENCES,
1402 enum_definition.variants[largest_index].span,
1403 fluent::lint_variant_size_differences,
1404 |lint| lint.set_arg("largest", largest),
1412 /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1413 /// to an atomic operation that does not support that ordering.
1417 /// ```rust,compile_fail
1418 /// # use core::sync::atomic::{AtomicU8, Ordering};
1419 /// let atom = AtomicU8::new(0);
1420 /// let value = atom.load(Ordering::Release);
1421 /// # let _ = value;
1428 /// Some atomic operations are only supported for a subset of the
1429 /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1430 /// an unconditional panic at runtime, which is detected by this lint.
1432 /// This lint will trigger in the following cases: (where `AtomicType` is an
1433 /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1434 /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1436 /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1437 /// `AtomicType::store`.
1439 /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1440 /// `AtomicType::load`.
1442 /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1443 /// `core::sync::atomic::compiler_fence`.
1445 /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1446 /// ordering for any of `AtomicType::compare_exchange`,
1447 /// `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1448 INVALID_ATOMIC_ORDERING,
1450 "usage of invalid atomic ordering in atomic operations and memory fences"
1453 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1455 impl InvalidAtomicOrdering {
1456 fn inherent_atomic_method_call<'hir>(
1457 cx: &LateContext<'_>,
1459 recognized_names: &[Symbol], // used for fast path calculation
1460 ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1461 const ATOMIC_TYPES: &[Symbol] = &[
1477 if let ExprKind::MethodCall(ref method_path, _, args, _) = &expr.kind
1478 && recognized_names.contains(&method_path.ident.name)
1479 && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
1480 && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
1481 && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
1482 // skip extension traits, only lint functions from the standard library
1483 && cx.tcx.trait_id_of_impl(impl_did).is_none()
1484 && let parent = cx.tcx.parent(adt.did())
1485 && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
1486 && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
1488 return Some((method_path.ident.name, args));
1493 fn match_ordering(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<Symbol> {
1494 let ExprKind::Path(ref ord_qpath) = ord_arg.kind else { return None };
1495 let did = cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()?;
1497 let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1498 let name = tcx.item_name(did);
1499 let parent = tcx.parent(did);
1500 [sym::Relaxed, sym::Release, sym::Acquire, sym::AcqRel, sym::SeqCst].into_iter().find(
1503 && (Some(parent) == atomic_ordering
1504 // needed in case this is a ctor, not a variant
1505 || tcx.opt_parent(parent) == atomic_ordering)
1510 fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1511 if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
1512 && let Some((ordering_arg, invalid_ordering, msg)) = match method {
1513 sym::load => Some((&args[0], sym::Release, fluent::lint_atomic_ordering_load)),
1514 sym::store => Some((&args[1], sym::Acquire, fluent::lint_atomic_ordering_store)),
1517 && let Some(ordering) = Self::match_ordering(cx, ordering_arg)
1518 && (ordering == invalid_ordering || ordering == sym::AcqRel)
1520 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, msg, |lint| {
1521 lint.help(fluent::help)
1526 fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1527 if let ExprKind::Call(ref func, ref args) = expr.kind
1528 && let ExprKind::Path(ref func_qpath) = func.kind
1529 && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
1530 && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
1531 && Self::match_ordering(cx, &args[0]) == Some(sym::Relaxed)
1533 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, fluent::lint_atomic_ordering_fence, |lint| {
1540 fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1541 let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
1544 let fail_order_arg = match method {
1545 sym::fetch_update => &args[1],
1546 sym::compare_exchange | sym::compare_exchange_weak => &args[3],
1550 let Some(fail_ordering) = Self::match_ordering(cx, fail_order_arg) else { return };
1552 if matches!(fail_ordering, sym::Release | sym::AcqRel) {
1553 #[derive(LintDiagnostic)]
1554 #[diag(lint_atomic_ordering_invalid)]
1556 struct InvalidAtomicOrderingDiag {
1559 fail_order_arg_span: Span,
1562 cx.emit_spanned_lint(
1563 INVALID_ATOMIC_ORDERING,
1564 fail_order_arg.span,
1565 InvalidAtomicOrderingDiag { method, fail_order_arg_span: fail_order_arg.span },
1571 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1572 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1573 Self::check_atomic_load_store(cx, expr);
1574 Self::check_memory_fence(cx, expr);
1575 Self::check_atomic_compare_exchange(cx, expr);