1 use crate::{LateContext, LateLintPass, LintContext};
3 use rustc_attr as attr;
4 use rustc_data_structures::fx::FxHashSet;
5 use rustc_errors::Applicability;
7 use rustc_hir::def_id::DefId;
8 use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
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, TypeFoldable, TypeSuperFoldable};
12 use rustc_span::source_map;
13 use rustc_span::symbol::sym;
14 use rustc_span::{Span, Symbol, DUMMY_SP};
15 use rustc_target::abi::{Abi, WrappingRange};
16 use rustc_target::abi::{Integer, TagEncoding, Variants};
17 use rustc_target::spec::abi::Abi as SpecAbi;
21 use std::ops::ControlFlow;
25 /// The `unused_comparisons` lint detects comparisons made useless by
26 /// limits of the types involved.
40 /// A useless comparison may indicate a mistake, and should be fixed or
44 "comparisons made useless by limits of the types involved"
48 /// The `overflowing_literals` lint detects literal out of range for its
53 /// ```rust,compile_fail
61 /// It is usually a mistake to use a literal that overflows the type where
62 /// it is used. Either use a literal that is within range, or change the
63 /// type to be within the range of the literal.
66 "literal out of range for its type"
70 /// The `variant_size_differences` lint detects enums with widely varying
75 /// ```rust,compile_fail
76 /// #![deny(variant_size_differences)]
87 /// It can be a mistake to add a variant to an enum that is much larger
88 /// than the other variants, bloating the overall size required for all
89 /// variants. This can impact performance and memory usage. This is
90 /// triggered if one variant is more than 3 times larger than the
91 /// second-largest variant.
93 /// Consider placing the large variant's contents on the heap (for example
94 /// via [`Box`]) to keep the overall size of the enum itself down.
96 /// This lint is "allow" by default because it can be noisy, and may not be
97 /// an actual problem. Decisions about this should be guided with
98 /// profiling and benchmarking.
100 /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html
101 VARIANT_SIZE_DIFFERENCES,
103 "detects enums with widely varying variant sizes"
106 #[derive(Copy, Clone)]
107 pub struct TypeLimits {
108 /// Id of the last visited negated expression
109 negated_expr_id: Option<hir::HirId>,
112 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
115 pub fn new() -> TypeLimits {
116 TypeLimits { negated_expr_id: None }
120 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
121 /// Returns `true` iff the lint was overridden.
122 fn lint_overflowing_range_endpoint<'tcx>(
123 cx: &LateContext<'tcx>,
127 expr: &'tcx hir::Expr<'tcx>,
128 parent_expr: &'tcx hir::Expr<'tcx>,
131 // We only want to handle exclusive (`..`) ranges,
132 // which are represented as `ExprKind::Struct`.
133 let mut overwritten = false;
134 if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
138 // We can suggest using an inclusive range
139 // (`..=`) instead only if it is the `end` that is
140 // overflowing and only by 1.
141 if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
142 cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| {
143 let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty));
144 if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
145 use ast::{LitIntType, LitKind};
146 // We need to preserve the literal's suffix,
147 // as it may determine typing information.
148 let suffix = match lit.node {
149 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
150 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
151 LitKind::Int(_, LitIntType::Unsuffixed) => "",
154 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
157 "use an inclusive range instead",
159 Applicability::MachineApplicable,
170 // For `isize` & `usize`, be conservative with the warnings, so that the
171 // warnings are consistent between 32- and 64-bit platforms.
172 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
174 ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
175 ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
176 ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
177 ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
178 ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
179 ty::IntTy::I128 => (i128::MIN, i128::MAX),
183 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
184 let max = match uint_ty {
185 ty::UintTy::Usize => u64::MAX.into(),
186 ty::UintTy::U8 => u8::MAX.into(),
187 ty::UintTy::U16 => u16::MAX.into(),
188 ty::UintTy::U32 => u32::MAX.into(),
189 ty::UintTy::U64 => u64::MAX.into(),
190 ty::UintTy::U128 => u128::MAX,
195 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
196 let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
197 let firstch = src.chars().next()?;
200 match src.chars().nth(1) {
201 Some('x' | 'b') => return Some(src),
209 fn report_bin_hex_error(
210 cx: &LateContext<'_>,
211 expr: &hir::Expr<'_>,
217 let size = Integer::from_attr(&cx.tcx, ty).size();
218 cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
219 let (t, actually) = match ty {
220 attr::IntType::SignedInt(t) => {
221 let actually = if negative {
222 -(size.sign_extend(val) as i128)
224 size.sign_extend(val) as i128
226 (t.name_str(), actually.to_string())
228 attr::IntType::UnsignedInt(t) => {
229 let actually = size.truncate(val);
230 (t.name_str(), actually.to_string())
233 let mut err = lint.build(&format!("literal out of range for `{}`", t));
235 // If the value is negative,
236 // emits a note about the value itself, apart from the literal.
238 "the literal `{}` (decimal `{}`) does not fit into \
242 err.note(&format!("and the value `-{}` will become `{}{}`", repr_str, actually, t));
245 "the literal `{}` (decimal `{}`) does not fit into \
246 the type `{}` and will become `{}{}`",
247 repr_str, val, t, actually, t
250 if let Some(sugg_ty) =
251 get_type_suggestion(cx.typeck_results().node_type(expr.hir_id), val, negative)
253 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
254 let (sans_suffix, _) = repr_str.split_at(pos);
257 &format!("consider using the type `{}` instead", sugg_ty),
258 format!("{}{}", sans_suffix, sugg_ty),
259 Applicability::MachineApplicable,
262 err.help(&format!("consider using the type `{}` instead", sugg_ty));
269 // This function finds the next fitting type and generates a suggestion string.
270 // It searches for fitting types in the following way (`X < Y`):
271 // - `iX`: if literal fits in `uX` => `uX`, else => `iY`
275 // No suggestion for: `isize`, `usize`.
276 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
279 macro_rules! find_fit {
280 ($ty:expr, $val:expr, $negative:expr,
281 $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
283 let _neg = if negative { 1 } else { 0 };
286 $(if !negative && val <= uint_ty_range($utypes).1 {
287 return Some($utypes.name_str())
289 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
290 return Some($itypes.name_str())
300 ty::Int(i) => find_fit!(i, val, negative,
301 I8 => [U8] => [I16, I32, I64, I128],
302 I16 => [U16] => [I32, I64, I128],
303 I32 => [U32] => [I64, I128],
304 I64 => [U64] => [I128],
305 I128 => [U128] => []),
306 ty::Uint(u) => find_fit!(u, val, negative,
307 U8 => [U8, U16, U32, U64, U128] => [],
308 U16 => [U16, U32, U64, U128] => [],
309 U32 => [U32, U64, U128] => [],
310 U64 => [U64, U128] => [],
311 U128 => [U128] => []),
316 fn lint_int_literal<'tcx>(
317 cx: &LateContext<'tcx>,
318 type_limits: &TypeLimits,
319 e: &'tcx hir::Expr<'tcx>,
324 let int_type = t.normalize(cx.sess().target.pointer_width);
325 let (min, max) = int_ty_range(int_type);
326 let max = max as u128;
327 let negative = type_limits.negated_expr_id == Some(e.hir_id);
329 // Detect literal value out of range [min, max] inclusive
330 // avoiding use of -min to prevent overflow/panic
331 if (negative && v > max + 1) || (!negative && v > max) {
332 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
333 report_bin_hex_error(
336 attr::IntType::SignedInt(ty::ast_int_ty(t)),
344 let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
345 if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
346 if let hir::ExprKind::Struct(..) = par_e.kind {
347 if is_range_literal(par_e)
348 && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
350 // The overflowing literal lint was overridden.
356 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
357 let mut err = lint.build(&format!("literal out of range for `{}`", t.name_str()));
359 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
362 .span_to_snippet(lit.span)
363 .expect("must get snippet from literal"),
368 if let Some(sugg_ty) =
369 get_type_suggestion(cx.typeck_results().node_type(e.hir_id), v, negative)
371 err.help(&format!("consider using the type `{}` instead", sugg_ty));
378 fn lint_uint_literal<'tcx>(
379 cx: &LateContext<'tcx>,
380 e: &'tcx hir::Expr<'tcx>,
384 let uint_type = t.normalize(cx.sess().target.pointer_width);
385 let (min, max) = uint_ty_range(uint_type);
386 let lit_val: u128 = match lit.node {
387 // _v is u8, within range by definition
388 ast::LitKind::Byte(_v) => return,
389 ast::LitKind::Int(v, _) => v,
392 if lit_val < min || lit_val > max {
393 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
394 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
396 hir::ExprKind::Cast(..) => {
397 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
398 cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
399 lint.build("only `u8` can be cast into `char`")
402 "use a `char` literal instead",
403 format!("'\\u{{{:X}}}'", lit_val),
404 Applicability::MachineApplicable,
411 hir::ExprKind::Struct(..) if is_range_literal(par_e) => {
412 let t = t.name_str();
413 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
414 // The overflowing literal lint was overridden.
421 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
422 report_bin_hex_error(
425 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
432 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
433 lint.build(&format!("literal out of range for `{}`", t.name_str()))
435 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
438 .span_to_snippet(lit.span)
439 .expect("must get snippet from literal"),
449 fn lint_literal<'tcx>(
450 cx: &LateContext<'tcx>,
451 type_limits: &TypeLimits,
452 e: &'tcx hir::Expr<'tcx>,
455 match *cx.typeck_results().node_type(e.hir_id).kind() {
458 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
459 lint_int_literal(cx, type_limits, e, lit, t, v)
464 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
466 let is_infinite = match lit.node {
467 ast::LitKind::Float(v, _) => match t {
468 ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
469 ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
473 if is_infinite == Ok(true) {
474 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
475 lint.build(&format!("literal out of range for `{}`", t.name_str()))
477 "the literal `{}` does not fit into the type `{}` and will be converted to `{}::INFINITY`",
480 .span_to_snippet(lit.span)
481 .expect("must get snippet from literal"),
493 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
494 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
496 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
497 // propagate negation, if the negation itself isn't negated
498 if self.negated_expr_id != Some(e.hir_id) {
499 self.negated_expr_id = Some(expr.hir_id);
502 hir::ExprKind::Binary(binop, ref l, ref r) => {
503 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
504 cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
505 lint.build("comparison is useless due to type limits").emit();
509 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
513 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
515 hir::BinOpKind::Lt => v > min && v <= max,
516 hir::BinOpKind::Le => v >= min && v < max,
517 hir::BinOpKind::Gt => v >= min && v < max,
518 hir::BinOpKind::Ge => v > min && v <= max,
519 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
524 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
528 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
529 hir::BinOpKind::Le => hir::BinOpKind::Ge,
530 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
531 hir::BinOpKind::Ge => hir::BinOpKind::Le,
538 cx: &LateContext<'_>,
543 let (lit, expr, swap) = match (&l.kind, &r.kind) {
544 (&hir::ExprKind::Lit(_), _) => (l, r, true),
545 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
548 // Normalize the binop so that the literal is always on the RHS in
550 let norm_binop = if swap { rev_binop(binop) } else { binop };
551 match *cx.typeck_results().node_type(expr.hir_id).kind() {
553 let (min, max) = int_ty_range(int_ty);
554 let lit_val: i128 = match lit.kind {
555 hir::ExprKind::Lit(ref li) => match li.node {
558 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
564 is_valid(norm_binop, lit_val, min, max)
566 ty::Uint(uint_ty) => {
567 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
568 let lit_val: u128 = match lit.kind {
569 hir::ExprKind::Lit(ref li) => match li.node {
570 ast::LitKind::Int(v, _) => v,
575 is_valid(norm_binop, lit_val, min, max)
581 fn is_comparison(binop: hir::BinOp) -> bool {
596 /// The `improper_ctypes` lint detects incorrect use of types in foreign
603 /// static STATIC: String;
611 /// The compiler has several checks to verify that types used in `extern`
612 /// blocks are safe and follow certain rules to ensure proper
613 /// compatibility with the foreign interfaces. This lint is issued when it
614 /// detects a probable mistake in a definition. The lint usually should
615 /// provide a description of the issue, along with possibly a hint on how
619 "proper use of libc types in foreign modules"
622 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
625 /// The `improper_ctypes_definitions` lint detects incorrect use of
626 /// [`extern` function] definitions.
628 /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
633 /// # #![allow(unused)]
634 /// pub extern "C" fn str_type(p: &str) { }
641 /// There are many parameter and return types that may be specified in an
642 /// `extern` function that are not compatible with the given ABI. This
643 /// lint is an alert that these types should not be used. The lint usually
644 /// should provide a description of the issue, along with possibly a hint
645 /// on how to resolve it.
646 IMPROPER_CTYPES_DEFINITIONS,
648 "proper use of libc types in foreign item definitions"
651 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
653 #[derive(Clone, Copy)]
654 pub(crate) enum CItemKind {
659 struct ImproperCTypesVisitor<'a, 'tcx> {
660 cx: &'a LateContext<'tcx>,
664 enum FfiResult<'tcx> {
666 FfiPhantom(Ty<'tcx>),
667 FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option<String> },
670 pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
672 def: ty::AdtDef<'tcx>,
674 tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
677 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
679 pub fn transparent_newtype_field<'a, 'tcx>(
681 variant: &'a ty::VariantDef,
682 ) -> Option<&'a ty::FieldDef> {
683 let param_env = tcx.param_env(variant.def_id);
684 variant.fields.iter().find(|field| {
685 let field_ty = tcx.type_of(field.did);
686 let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
691 /// Is type known to be non-null?
692 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
695 ty::FnPtr(_) => true,
697 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
698 ty::Adt(def, substs) if def.repr().transparent() && !def.is_union() => {
699 let marked_non_null = nonnull_optimization_guaranteed(tcx, *def);
705 // Types with a `#[repr(no_niche)]` attribute have their niche hidden.
706 // The attribute is used by the UnsafeCell for example (the only use so far).
707 if def.repr().hide_niche() {
713 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
714 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
720 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
721 /// If the type passed in was not scalar, returns None.
722 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
724 Some(match *ty.kind() {
725 ty::Adt(field_def, field_substs) => {
726 let inner_field_ty = {
727 let first_non_zst_ty = field_def
730 .filter_map(|v| transparent_newtype_field(cx.tcx, v));
732 first_non_zst_ty.clone().count(),
734 "Wrong number of fields for transparent type"
738 .expect("No non-zst fields in transparent type.")
739 .ty(tcx, field_substs)
741 return get_nullable_type(cx, inner_field_ty);
743 ty::Int(ty) => tcx.mk_mach_int(ty),
744 ty::Uint(ty) => tcx.mk_mach_uint(ty),
745 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
746 // As these types are always non-null, the nullable equivalent of
747 // Option<T> of these types are their raw pointer counterparts.
748 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
750 // There is no nullable equivalent for Rust's function pointers -- you
751 // must use an Option<fn(..) -> _> to represent it.
755 // We should only ever reach this case if ty_is_known_nonnull is extended
759 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
767 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
768 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
769 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
770 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
771 /// FIXME: This duplicates code in codegen.
772 pub(crate) fn repr_nullable_ptr<'tcx>(
773 cx: &LateContext<'tcx>,
776 ) -> Option<Ty<'tcx>> {
777 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
778 if let ty::Adt(ty_def, substs) = ty.kind() {
779 let field_ty = match &ty_def.variants().raw[..] {
780 [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
781 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
787 if !ty_is_known_nonnull(cx, field_ty, ckind) {
791 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
792 // If the computed size for the field and the enum are different, the nonnull optimization isn't
793 // being applied (and we've got a problem somewhere).
794 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
795 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
796 bug!("improper_ctypes: Option nonnull optimization not applied?");
799 // Return the nullable type this Option-like enum can be safely represented with.
800 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
801 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
802 match field_ty_scalar.valid_range(cx) {
803 WrappingRange { start: 0, end }
804 if end == field_ty_scalar.size(&cx.tcx).unsigned_int_max() - 1 =>
806 return Some(get_nullable_type(cx, field_ty).unwrap());
808 WrappingRange { start: 1, .. } => {
809 return Some(get_nullable_type(cx, field_ty).unwrap());
811 WrappingRange { start, end } => {
812 unreachable!("Unhandled start and end range: ({}, {})", start, end)
820 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
821 /// Check if the type is array and emit an unsafe type lint.
822 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
823 if let ty::Array(..) = ty.kind() {
824 self.emit_ffi_unsafe_type_lint(
827 "passing raw arrays by value is not FFI-safe",
828 Some("consider passing a pointer to the array"),
836 /// Checks if the given field's type is "ffi-safe".
837 fn check_field_type_for_ffi(
839 cache: &mut FxHashSet<Ty<'tcx>>,
840 field: &ty::FieldDef,
841 substs: SubstsRef<'tcx>,
842 ) -> FfiResult<'tcx> {
843 let field_ty = field.ty(self.cx.tcx, substs);
844 if field_ty.has_opaque_types() {
845 self.check_type_for_ffi(cache, field_ty)
847 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
848 self.check_type_for_ffi(cache, field_ty)
852 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
853 fn check_variant_for_ffi(
855 cache: &mut FxHashSet<Ty<'tcx>>,
857 def: ty::AdtDef<'tcx>,
858 variant: &ty::VariantDef,
859 substs: SubstsRef<'tcx>,
860 ) -> FfiResult<'tcx> {
863 if def.repr().transparent() {
864 // Can assume that at most one field is not a ZST, so only check
865 // that field's type for FFI-safety.
866 if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
867 self.check_field_type_for_ffi(cache, field, substs)
869 // All fields are ZSTs; this means that the type should behave
870 // like (), which is FFI-unsafe
873 reason: "this struct contains only zero-sized fields".into(),
878 // We can't completely trust repr(C) markings; make sure the fields are
880 let mut all_phantom = !variant.fields.is_empty();
881 for field in &variant.fields {
882 match self.check_field_type_for_ffi(cache, &field, substs) {
886 FfiPhantom(..) if def.is_enum() => {
889 reason: "this enum contains a PhantomData field".into(),
898 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
902 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
903 /// representation which can be exported to C code).
904 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
907 let tcx = self.cx.tcx;
909 // Protect against infinite recursion, for example
910 // `struct S(*mut S);`.
911 // FIXME: A recursion limit is necessary as well, for irregular
913 if !cache.insert(ty) {
918 ty::Adt(def, substs) => {
919 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
920 if ty.boxed_ty().is_sized(tcx.at(DUMMY_SP), self.cx.param_env) {
925 reason: "box cannot be represented as a single pointer".to_string(),
930 if def.is_phantom_data() {
931 return FfiPhantom(ty);
933 match def.adt_kind() {
934 AdtKind::Struct | AdtKind::Union => {
935 let kind = if def.is_struct() { "struct" } else { "union" };
937 if !def.repr().c() && !def.repr().transparent() {
940 reason: format!("this {} has unspecified layout", kind),
942 "consider adding a `#[repr(C)]` or \
943 `#[repr(transparent)]` attribute to this {}",
949 let is_non_exhaustive =
950 def.non_enum_variant().is_field_list_non_exhaustive();
951 if is_non_exhaustive && !def.did().is_local() {
954 reason: format!("this {} is non-exhaustive", kind),
959 if def.non_enum_variant().fields.is_empty() {
962 reason: format!("this {} has no fields", kind),
963 help: Some(format!("consider adding a member to this {}", kind)),
967 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
970 if def.variants().is_empty() {
971 // Empty enums are okay... although sort of useless.
975 // Check for a repr() attribute to specify the size of the
977 if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
979 // Special-case types like `Option<extern fn()>`.
980 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
983 reason: "enum has no representation hint".into(),
985 "consider adding a `#[repr(C)]`, \
986 `#[repr(transparent)]`, or integer `#[repr(...)]` \
987 attribute to this enum"
994 if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
997 reason: "this enum is non-exhaustive".into(),
1002 // Check the contained variants.
1003 for variant in def.variants() {
1004 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1005 if is_non_exhaustive && !variant.def_id.is_local() {
1008 reason: "this enum has non-exhaustive variants".into(),
1013 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1024 ty::Char => FfiUnsafe {
1026 reason: "the `char` type has no C equivalent".into(),
1027 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
1030 ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => FfiUnsafe {
1032 reason: "128-bit integers don't currently have a known stable ABI".into(),
1036 // Primitive types with a stable representation.
1037 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1039 ty::Slice(_) => FfiUnsafe {
1041 reason: "slices have no C equivalent".into(),
1042 help: Some("consider using a raw pointer instead".into()),
1045 ty::Dynamic(..) => {
1046 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
1049 ty::Str => FfiUnsafe {
1051 reason: "string slices have no C equivalent".into(),
1052 help: Some("consider using `*const u8` and a length instead".into()),
1055 ty::Tuple(..) => FfiUnsafe {
1057 reason: "tuples have unspecified layout".into(),
1058 help: Some("consider using a struct instead".into()),
1061 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1063 matches!(self.mode, CItemKind::Definition)
1064 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1070 ty::RawPtr(ty::TypeAndMut { ty, .. })
1071 if match ty.kind() {
1072 ty::Tuple(tuple) => tuple.is_empty(),
1079 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1080 self.check_type_for_ffi(cache, ty)
1083 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1086 if self.is_internal_abi(sig.abi()) {
1089 reason: "this function pointer has Rust-specific calling convention".into(),
1091 "consider using an `extern fn(...) -> ...` \
1092 function pointer instead"
1098 let sig = tcx.erase_late_bound_regions(sig);
1099 if !sig.output().is_unit() {
1100 let r = self.check_type_for_ffi(cache, sig.output());
1108 for arg in sig.inputs() {
1109 let r = self.check_type_for_ffi(cache, *arg);
1120 ty::Foreign(..) => FfiSafe,
1122 // While opaque types are checked for earlier, if a projection in a struct field
1123 // normalizes to an opaque type, then it will reach this branch.
1125 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
1128 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1129 // so they are currently ignored for the purposes of this lint.
1130 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1135 | ty::Projection(..)
1141 | ty::GeneratorWitness(..)
1142 | ty::Placeholder(..)
1143 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1147 fn emit_ffi_unsafe_type_lint(
1154 let lint = match self.mode {
1155 CItemKind::Declaration => IMPROPER_CTYPES,
1156 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1159 self.cx.struct_span_lint(lint, sp, |lint| {
1160 let item_description = match self.mode {
1161 CItemKind::Declaration => "block",
1162 CItemKind::Definition => "fn",
1164 let mut diag = lint.build(&format!(
1165 "`extern` {} uses type `{}`, which is not FFI-safe",
1166 item_description, ty
1168 diag.span_label(sp, "not FFI-safe");
1169 if let Some(help) = help {
1173 if let ty::Adt(def, _) = ty.kind() {
1174 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did()) {
1175 diag.span_note(sp, "the type is defined here");
1182 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1183 struct ProhibitOpaqueTypes<'a, 'tcx> {
1184 cx: &'a LateContext<'tcx>,
1187 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1188 type BreakTy = Ty<'tcx>;
1190 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1192 ty::Opaque(..) => ControlFlow::Break(ty),
1193 // Consider opaque types within projections FFI-safe if they do not normalize
1194 // to more opaque types.
1195 ty::Projection(..) => {
1196 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1198 // If `ty` is an opaque type directly then `super_visit_with` won't invoke
1199 // this function again.
1200 if ty.has_opaque_types() {
1203 ControlFlow::CONTINUE
1206 _ => ty.super_visit_with(self),
1211 if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1212 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
1219 fn check_type_for_ffi_and_report_errors(
1224 is_return_type: bool,
1226 // We have to check for opaque types before `normalize_erasing_regions`,
1227 // which will replace opaque types with their underlying concrete type.
1228 if self.check_for_opaque_ty(sp, ty) {
1229 // We've already emitted an error due to an opaque type.
1233 // it is only OK to use this function because extern fns cannot have
1234 // any generic types right now:
1235 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1237 // C doesn't really support passing arrays by value - the only way to pass an array by value
1238 // is through a struct. So, first test that the top level isn't an array, and then
1239 // recursively check the types inside.
1240 if !is_static && self.check_for_array_ty(sp, ty) {
1244 // Don't report FFI errors for unit return types. This check exists here, and not in
1245 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1247 if is_return_type && ty.is_unit() {
1251 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1252 FfiResult::FfiSafe => {}
1253 FfiResult::FfiPhantom(ty) => {
1254 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1256 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1257 // argument, which after substitution, is `()`, then this branch can be hit.
1258 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1259 FfiResult::FfiUnsafe { ty, reason, help } => {
1260 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1265 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1266 let def_id = self.cx.tcx.hir().local_def_id(id);
1267 let sig = self.cx.tcx.fn_sig(def_id);
1268 let sig = self.cx.tcx.erase_late_bound_regions(sig);
1270 for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1271 self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
1274 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1275 let ret_ty = sig.output();
1276 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1280 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1281 let def_id = self.cx.tcx.hir().local_def_id(id);
1282 let ty = self.cx.tcx.type_of(def_id);
1283 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1286 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1289 SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1294 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1295 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1296 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1297 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1299 if !vis.is_internal_abi(abi) {
1301 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1302 vis.check_foreign_fn(it.hir_id(), decl);
1304 hir::ForeignItemKind::Static(ref ty, _) => {
1305 vis.check_foreign_static(it.hir_id(), ty.span);
1307 hir::ForeignItemKind::Type => (),
1313 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1316 cx: &LateContext<'tcx>,
1317 kind: hir::intravisit::FnKind<'tcx>,
1318 decl: &'tcx hir::FnDecl<'_>,
1319 _: &'tcx hir::Body<'_>,
1323 use hir::intravisit::FnKind;
1325 let abi = match kind {
1326 FnKind::ItemFn(_, _, header, ..) => header.abi,
1327 FnKind::Method(_, sig, ..) => sig.header.abi,
1331 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1332 if !vis.is_internal_abi(abi) {
1333 vis.check_foreign_fn(hir_id, decl);
1338 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1340 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1341 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1342 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1343 let t = cx.tcx.type_of(it.def_id);
1344 let ty = cx.tcx.erase_regions(t);
1345 let Ok(layout) = cx.layout_of(ty) else { return };
1346 let Variants::Multiple {
1347 tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1348 } = &layout.variants else {
1352 let tag_size = tag.size(&cx.tcx).bytes();
1355 "enum `{}` is {} bytes large with layout:\n{:#?}",
1357 layout.size.bytes(),
1361 let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1362 .map(|(variant, variant_layout)| {
1363 // Subtract the size of the enum tag.
1364 let bytes = variant_layout.size().bytes().saturating_sub(tag_size);
1366 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1370 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1373 } else if size > s {
1380 // We only warn if the largest variant is at least thrice as large as
1381 // the second-largest.
1382 if largest > slargest * 3 && slargest > 0 {
1383 cx.struct_span_lint(
1384 VARIANT_SIZE_DIFFERENCES,
1385 enum_definition.variants[largest_index].span,
1387 lint.build(&format!(
1388 "enum variant is more than three times \
1389 larger ({} bytes) than the next largest",
1401 /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1402 /// to an atomic operation that does not support that ordering.
1406 /// ```rust,compile_fail
1407 /// # use core::sync::atomic::{AtomicU8, Ordering};
1408 /// let atom = AtomicU8::new(0);
1409 /// let value = atom.load(Ordering::Release);
1410 /// # let _ = value;
1417 /// Some atomic operations are only supported for a subset of the
1418 /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1419 /// an unconditional panic at runtime, which is detected by this lint.
1421 /// This lint will trigger in the following cases: (where `AtomicType` is an
1422 /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1423 /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1425 /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1426 /// `AtomicType::store`.
1428 /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1429 /// `AtomicType::load`.
1431 /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1432 /// `core::sync::atomic::compiler_fence`.
1434 /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1435 /// ordering for any of `AtomicType::compare_exchange`,
1436 /// `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1438 /// - Passing in a pair of orderings to `AtomicType::compare_exchange`,
1439 /// `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`
1440 /// where the failure ordering is stronger than the success ordering.
1441 INVALID_ATOMIC_ORDERING,
1443 "usage of invalid atomic ordering in atomic operations and memory fences"
1446 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1448 impl InvalidAtomicOrdering {
1449 fn inherent_atomic_method_call<'hir>(
1450 cx: &LateContext<'_>,
1452 recognized_names: &[Symbol], // used for fast path calculation
1453 ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1454 const ATOMIC_TYPES: &[Symbol] = &[
1470 if let ExprKind::MethodCall(ref method_path, args, _) = &expr.kind
1471 && recognized_names.contains(&method_path.ident.name)
1472 && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
1473 && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
1474 && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
1475 // skip extension traits, only lint functions from the standard library
1476 && cx.tcx.trait_id_of_impl(impl_did).is_none()
1477 && let parent = cx.tcx.parent(adt.did())
1478 && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
1479 && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
1481 return Some((method_path.ident.name, args));
1486 fn matches_ordering(cx: &LateContext<'_>, did: DefId, orderings: &[Symbol]) -> bool {
1488 let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1489 orderings.iter().any(|ordering| {
1490 tcx.item_name(did) == *ordering && {
1491 let parent = tcx.parent(did);
1492 Some(parent) == atomic_ordering
1493 // needed in case this is a ctor, not a variant
1494 || tcx.opt_parent(parent) == atomic_ordering
1499 fn opt_ordering_defid(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<DefId> {
1500 if let ExprKind::Path(ref ord_qpath) = ord_arg.kind {
1501 cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()
1507 fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1508 use rustc_hir::def::{DefKind, Res};
1509 use rustc_hir::QPath;
1510 if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
1511 && let Some((ordering_arg, invalid_ordering)) = match method {
1512 sym::load => Some((&args[1], sym::Release)),
1513 sym::store => Some((&args[2], sym::Acquire)),
1516 && let ExprKind::Path(QPath::Resolved(_, path)) = ordering_arg.kind
1517 && let Res::Def(DefKind::Ctor(..), ctor_id) = path.res
1518 && Self::matches_ordering(cx, ctor_id, &[invalid_ordering, sym::AcqRel])
1520 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, |diag| {
1521 if method == sym::load {
1522 diag.build("atomic loads cannot have `Release` or `AcqRel` ordering")
1523 .help("consider using ordering modes `Acquire`, `SeqCst` or `Relaxed`")
1526 debug_assert_eq!(method, sym::store);
1527 diag.build("atomic stores cannot have `Acquire` or `AcqRel` ordering")
1528 .help("consider using ordering modes `Release`, `SeqCst` or `Relaxed`")
1535 fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1536 if let ExprKind::Call(ref func, ref args) = expr.kind
1537 && let ExprKind::Path(ref func_qpath) = func.kind
1538 && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
1539 && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
1540 && let ExprKind::Path(ref ordering_qpath) = &args[0].kind
1541 && let Some(ordering_def_id) = cx.qpath_res(ordering_qpath, args[0].hir_id).opt_def_id()
1542 && Self::matches_ordering(cx, ordering_def_id, &[sym::Relaxed])
1544 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, |diag| {
1545 diag.build("memory fences cannot have `Relaxed` ordering")
1546 .help("consider using ordering modes `Acquire`, `Release`, `AcqRel` or `SeqCst`")
1552 fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1553 if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
1554 && let Some((success_order_arg, failure_order_arg)) = match method {
1555 sym::fetch_update => Some((&args[1], &args[2])),
1556 sym::compare_exchange | sym::compare_exchange_weak => Some((&args[3], &args[4])),
1559 && let Some(fail_ordering_def_id) = Self::opt_ordering_defid(cx, failure_order_arg)
1561 // Helper type holding on to some checking and error reporting data. Has
1562 // - (success ordering,
1563 // - list of failure orderings forbidden by the success order,
1564 // - suggestion message)
1565 type OrdLintInfo = (Symbol, &'static [Symbol], &'static str);
1566 const RELAXED: OrdLintInfo = (sym::Relaxed, &[sym::SeqCst, sym::Acquire], "ordering mode `Relaxed`");
1567 const ACQUIRE: OrdLintInfo = (sym::Acquire, &[sym::SeqCst], "ordering modes `Acquire` or `Relaxed`");
1568 const SEQ_CST: OrdLintInfo = (sym::SeqCst, &[], "ordering modes `Acquire`, `SeqCst` or `Relaxed`");
1569 const RELEASE: OrdLintInfo = (sym::Release, RELAXED.1, RELAXED.2);
1570 const ACQREL: OrdLintInfo = (sym::AcqRel, ACQUIRE.1, ACQUIRE.2);
1571 const SEARCH: [OrdLintInfo; 5] = [RELAXED, ACQUIRE, SEQ_CST, RELEASE, ACQREL];
1573 let success_lint_info = Self::opt_ordering_defid(cx, success_order_arg)
1574 .and_then(|success_ord_def_id| -> Option<OrdLintInfo> {
1578 .find(|(ordering, ..)| {
1579 Self::matches_ordering(cx, success_ord_def_id, &[*ordering])
1582 if Self::matches_ordering(cx, fail_ordering_def_id, &[sym::Release, sym::AcqRel]) {
1583 // If we don't know the success order is, use what we'd suggest
1584 // if it were maximally permissive.
1585 let suggested = success_lint_info.unwrap_or(SEQ_CST).2;
1586 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, failure_order_arg.span, |diag| {
1588 "{}'s failure ordering may not be `Release` or `AcqRel`",
1592 .help(&format!("consider using {} instead", suggested))
1595 } else if let Some((success_ord, bad_ords_given_success, suggested)) = success_lint_info {
1596 if Self::matches_ordering(cx, fail_ordering_def_id, bad_ords_given_success) {
1597 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, failure_order_arg.span, |diag| {
1599 "{}'s failure ordering may not be stronger than the success ordering of `{}`",
1604 .help(&format!("consider using {} instead", suggested))
1613 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1614 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1615 Self::check_atomic_load_store(cx, expr);
1616 Self::check_memory_fence(cx, expr);
1617 Self::check_atomic_compare_exchange(cx, expr);