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::{is_range_literal, ExprKind, Node};
8 use rustc_index::vec::Idx;
9 use rustc_middle::ty::layout::{IntegerExt, SizeSkeleton};
10 use rustc_middle::ty::subst::SubstsRef;
11 use rustc_middle::ty::{self, AdtKind, Ty, TyCtxt, TypeFoldable};
12 use rustc_span::source_map;
13 use rustc_span::symbol::sym;
14 use rustc_span::{Span, DUMMY_SP};
15 use rustc_target::abi::Abi;
16 use rustc_target::abi::{Integer, LayoutOf, TagEncoding, VariantIdx, 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 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 crate fn nonnull_optimization_guaranteed<'tcx>(tcx: TyCtxt<'tcx>, def: &ty::AdtDef) -> bool {
671 tcx.get_attrs(def.did)
673 .any(|a| tcx.sess.check_name(a, sym::rustc_nonnull_optimization_guaranteed))
676 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
678 pub fn transparent_newtype_field<'a, 'tcx>(
680 variant: &'a ty::VariantDef,
681 ) -> Option<&'a ty::FieldDef> {
682 let param_env = tcx.param_env(variant.def_id);
683 for field in &variant.fields {
684 let field_ty = tcx.type_of(field.did);
685 let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
695 /// Is type known to be non-null?
696 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
699 ty::FnPtr(_) => true,
701 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
702 ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
703 let marked_non_null = nonnull_optimization_guaranteed(tcx, &def);
709 // Types with a `#[repr(no_niche)]` attribute have their niche hidden.
710 // The attribute is used by the UnsafeCell for example (the only use so far).
711 if def.repr.hide_niche() {
715 for variant in &def.variants {
716 if let Some(field) = transparent_newtype_field(cx.tcx, variant) {
717 if ty_is_known_nonnull(cx, field.ty(tcx, substs), mode) {
729 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
730 /// If the type passed in was not scalar, returns None.
731 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
733 Some(match *ty.kind() {
734 ty::Adt(field_def, field_substs) => {
735 let inner_field_ty = {
736 let first_non_zst_ty =
737 field_def.variants.iter().filter_map(|v| transparent_newtype_field(cx.tcx, v));
739 first_non_zst_ty.clone().count(),
741 "Wrong number of fields for transparent type"
745 .expect("No non-zst fields in transparent type.")
746 .ty(tcx, field_substs)
748 return get_nullable_type(cx, inner_field_ty);
750 ty::Int(ty) => tcx.mk_mach_int(ty),
751 ty::Uint(ty) => tcx.mk_mach_uint(ty),
752 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
753 // As these types are always non-null, the nullable equivalent of
754 // Option<T> of these types are their raw pointer counterparts.
755 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
757 // There is no nullable equivalent for Rust's function pointers -- you
758 // must use an Option<fn(..) -> _> to represent it.
762 // We should only ever reach this case if ty_is_known_nonnull is extended
766 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
774 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
775 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
776 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
777 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
778 /// FIXME: This duplicates code in codegen.
779 crate fn repr_nullable_ptr<'tcx>(
780 cx: &LateContext<'tcx>,
783 ) -> Option<Ty<'tcx>> {
784 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
785 if let ty::Adt(ty_def, substs) = ty.kind() {
786 if ty_def.variants.len() != 2 {
790 let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
791 let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
792 let fields = if variant_fields[0].is_empty() {
794 } else if variant_fields[1].is_empty() {
800 if fields.len() != 1 {
804 let field_ty = fields[0].ty(cx.tcx, substs);
805 if !ty_is_known_nonnull(cx, field_ty, ckind) {
809 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
810 // If the computed size for the field and the enum are different, the nonnull optimization isn't
811 // being applied (and we've got a problem somewhere).
812 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
813 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
814 bug!("improper_ctypes: Option nonnull optimization not applied?");
817 // Return the nullable type this Option-like enum can be safely represented with.
818 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
819 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
820 match (field_ty_scalar.valid_range.start(), field_ty_scalar.valid_range.end()) {
821 (0, _) => unreachable!("Non-null optimisation extended to a non-zero value."),
823 return Some(get_nullable_type(cx, field_ty).unwrap());
825 (start, end) => unreachable!("Unhandled start and end range: ({}, {})", start, end),
832 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
833 /// Check if the type is array and emit an unsafe type lint.
834 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
835 if let ty::Array(..) = ty.kind() {
836 self.emit_ffi_unsafe_type_lint(
839 "passing raw arrays by value is not FFI-safe",
840 Some("consider passing a pointer to the array"),
848 /// Checks if the given field's type is "ffi-safe".
849 fn check_field_type_for_ffi(
851 cache: &mut FxHashSet<Ty<'tcx>>,
852 field: &ty::FieldDef,
853 substs: SubstsRef<'tcx>,
854 ) -> FfiResult<'tcx> {
855 let field_ty = field.ty(self.cx.tcx, substs);
856 if field_ty.has_opaque_types() {
857 self.check_type_for_ffi(cache, field_ty)
859 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
860 self.check_type_for_ffi(cache, field_ty)
864 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
865 fn check_variant_for_ffi(
867 cache: &mut FxHashSet<Ty<'tcx>>,
870 variant: &ty::VariantDef,
871 substs: SubstsRef<'tcx>,
872 ) -> FfiResult<'tcx> {
875 if def.repr.transparent() {
876 // Can assume that only one field is not a ZST, so only check
877 // that field's type for FFI-safety.
878 if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
879 self.check_field_type_for_ffi(cache, field, substs)
881 bug!("malformed transparent type");
884 // We can't completely trust repr(C) markings; make sure the fields are
886 let mut all_phantom = !variant.fields.is_empty();
887 for field in &variant.fields {
888 match self.check_field_type_for_ffi(cache, &field, substs) {
892 FfiPhantom(..) if def.is_enum() => {
895 reason: "this enum contains a PhantomData field".into(),
904 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
908 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
909 /// representation which can be exported to C code).
910 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
913 let tcx = self.cx.tcx;
915 // Protect against infinite recursion, for example
916 // `struct S(*mut S);`.
917 // FIXME: A recursion limit is necessary as well, for irregular
919 if !cache.insert(ty) {
924 ty::Adt(def, _) if def.is_box() && matches!(self.mode, CItemKind::Definition) => {
928 ty::Adt(def, substs) => {
929 if def.is_phantom_data() {
930 return FfiPhantom(ty);
932 match def.adt_kind() {
933 AdtKind::Struct | AdtKind::Union => {
934 let kind = if def.is_struct() { "struct" } else { "union" };
936 if !def.repr.c() && !def.repr.transparent() {
939 reason: format!("this {} has unspecified layout", kind),
941 "consider adding a `#[repr(C)]` or \
942 `#[repr(transparent)]` attribute to this {}",
948 let is_non_exhaustive =
949 def.non_enum_variant().is_field_list_non_exhaustive();
950 if is_non_exhaustive && !def.did.is_local() {
953 reason: format!("this {} is non-exhaustive", kind),
958 if def.non_enum_variant().fields.is_empty() {
961 reason: format!("this {} has no fields", kind),
962 help: Some(format!("consider adding a member to this {}", kind)),
966 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
969 if def.variants.is_empty() {
970 // Empty enums are okay... although sort of useless.
974 // Check for a repr() attribute to specify the size of the
976 if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
977 // Special-case types like `Option<extern fn()>`.
978 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
981 reason: "enum has no representation hint".into(),
983 "consider adding a `#[repr(C)]`, \
984 `#[repr(transparent)]`, or integer `#[repr(...)]` \
985 attribute to this enum"
992 if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
995 reason: "this enum is non-exhaustive".into(),
1000 // Check the contained variants.
1001 for variant in &def.variants {
1002 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1003 if is_non_exhaustive && !variant.def_id.is_local() {
1006 reason: "this enum has non-exhaustive variants".into(),
1011 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1022 ty::Char => FfiUnsafe {
1024 reason: "the `char` type has no C equivalent".into(),
1025 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
1028 ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => FfiUnsafe {
1030 reason: "128-bit integers don't currently have a known stable ABI".into(),
1034 // Primitive types with a stable representation.
1035 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1037 ty::Slice(_) => FfiUnsafe {
1039 reason: "slices have no C equivalent".into(),
1040 help: Some("consider using a raw pointer instead".into()),
1043 ty::Dynamic(..) => {
1044 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
1047 ty::Str => FfiUnsafe {
1049 reason: "string slices have no C equivalent".into(),
1050 help: Some("consider using `*const u8` and a length instead".into()),
1053 ty::Tuple(..) => FfiUnsafe {
1055 reason: "tuples have unspecified layout".into(),
1056 help: Some("consider using a struct instead".into()),
1059 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1061 matches!(self.mode, CItemKind::Definition)
1062 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1068 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1069 self.check_type_for_ffi(cache, ty)
1072 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1075 if self.is_internal_abi(sig.abi()) {
1078 reason: "this function pointer has Rust-specific calling convention".into(),
1080 "consider using an `extern fn(...) -> ...` \
1081 function pointer instead"
1087 let sig = tcx.erase_late_bound_regions(sig);
1088 if !sig.output().is_unit() {
1089 let r = self.check_type_for_ffi(cache, sig.output());
1097 for arg in sig.inputs() {
1098 let r = self.check_type_for_ffi(cache, arg);
1109 ty::Foreign(..) => FfiSafe,
1111 // While opaque types are checked for earlier, if a projection in a struct field
1112 // normalizes to an opaque type, then it will reach this branch.
1114 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
1117 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1118 // so they are currently ignored for the purposes of this lint.
1119 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1124 | ty::Projection(..)
1130 | ty::GeneratorWitness(..)
1131 | ty::Placeholder(..)
1132 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1136 fn emit_ffi_unsafe_type_lint(
1143 let lint = match self.mode {
1144 CItemKind::Declaration => IMPROPER_CTYPES,
1145 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1148 self.cx.struct_span_lint(lint, sp, |lint| {
1149 let item_description = match self.mode {
1150 CItemKind::Declaration => "block",
1151 CItemKind::Definition => "fn",
1153 let mut diag = lint.build(&format!(
1154 "`extern` {} uses type `{}`, which is not FFI-safe",
1155 item_description, ty
1157 diag.span_label(sp, "not FFI-safe");
1158 if let Some(help) = help {
1162 if let ty::Adt(def, _) = ty.kind() {
1163 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
1164 diag.span_note(sp, "the type is defined here");
1171 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1172 struct ProhibitOpaqueTypes<'a, 'tcx> {
1173 cx: &'a LateContext<'tcx>,
1176 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1177 type BreakTy = Ty<'tcx>;
1179 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1181 ty::Opaque(..) => ControlFlow::Break(ty),
1182 // Consider opaque types within projections FFI-safe if they do not normalize
1183 // to more opaque types.
1184 ty::Projection(..) => {
1185 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1187 // If `ty` is a opaque type directly then `super_visit_with` won't invoke
1188 // this function again.
1189 if ty.has_opaque_types() {
1192 ControlFlow::CONTINUE
1195 _ => ty.super_visit_with(self),
1200 if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1201 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
1208 fn check_type_for_ffi_and_report_errors(
1213 is_return_type: bool,
1215 // We have to check for opaque types before `normalize_erasing_regions`,
1216 // which will replace opaque types with their underlying concrete type.
1217 if self.check_for_opaque_ty(sp, ty) {
1218 // We've already emitted an error due to an opaque type.
1222 // it is only OK to use this function because extern fns cannot have
1223 // any generic types right now:
1224 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1226 // C doesn't really support passing arrays by value - the only way to pass an array by value
1227 // is through a struct. So, first test that the top level isn't an array, and then
1228 // recursively check the types inside.
1229 if !is_static && self.check_for_array_ty(sp, ty) {
1233 // Don't report FFI errors for unit return types. This check exists here, and not in
1234 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1236 if is_return_type && ty.is_unit() {
1240 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1241 FfiResult::FfiSafe => {}
1242 FfiResult::FfiPhantom(ty) => {
1243 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1245 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1246 // argument, which after substitution, is `()`, then this branch can be hit.
1247 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1248 FfiResult::FfiUnsafe { ty, reason, help } => {
1249 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1254 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1255 let def_id = self.cx.tcx.hir().local_def_id(id);
1256 let sig = self.cx.tcx.fn_sig(def_id);
1257 let sig = self.cx.tcx.erase_late_bound_regions(sig);
1259 for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1260 self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false);
1263 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1264 let ret_ty = sig.output();
1265 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1269 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1270 let def_id = self.cx.tcx.hir().local_def_id(id);
1271 let ty = self.cx.tcx.type_of(def_id);
1272 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1275 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1278 SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1283 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1284 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1285 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1286 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1288 if !vis.is_internal_abi(abi) {
1290 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1291 vis.check_foreign_fn(it.hir_id(), decl);
1293 hir::ForeignItemKind::Static(ref ty, _) => {
1294 vis.check_foreign_static(it.hir_id(), ty.span);
1296 hir::ForeignItemKind::Type => (),
1302 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1305 cx: &LateContext<'tcx>,
1306 kind: hir::intravisit::FnKind<'tcx>,
1307 decl: &'tcx hir::FnDecl<'_>,
1308 _: &'tcx hir::Body<'_>,
1312 use hir::intravisit::FnKind;
1314 let abi = match kind {
1315 FnKind::ItemFn(_, _, header, ..) => header.abi,
1316 FnKind::Method(_, sig, ..) => sig.header.abi,
1320 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1321 if !vis.is_internal_abi(abi) {
1322 vis.check_foreign_fn(hir_id, decl);
1327 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1329 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1330 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1331 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1332 let t = cx.tcx.type_of(it.def_id);
1333 let ty = cx.tcx.erase_regions(t);
1334 let layout = match cx.layout_of(ty) {
1335 Ok(layout) => layout,
1337 ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
1340 let (variants, tag) = match layout.variants {
1341 Variants::Multiple {
1342 tag_encoding: TagEncoding::Direct,
1346 } => (variants, tag),
1350 let tag_size = tag.value.size(&cx.tcx).bytes();
1353 "enum `{}` is {} bytes large with layout:\n{:#?}",
1355 layout.size.bytes(),
1359 let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1360 .map(|(variant, variant_layout)| {
1361 // Subtract the size of the enum tag.
1362 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1364 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1368 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1371 } else if size > s {
1378 // We only warn if the largest variant is at least thrice as large as
1379 // the second-largest.
1380 if largest > slargest * 3 && slargest > 0 {
1381 cx.struct_span_lint(
1382 VARIANT_SIZE_DIFFERENCES,
1383 enum_definition.variants[largest_index].span,
1385 lint.build(&format!(
1386 "enum variant is more than three times \
1387 larger ({} bytes) than the next largest",