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;
20 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.
120 /// Returns `true` iff the lint was overridden.
121 fn lint_overflowing_range_endpoint<'tcx>(
122 cx: &LateContext<'tcx>,
126 expr: &'tcx hir::Expr<'tcx>,
127 parent_expr: &'tcx hir::Expr<'tcx>,
130 // We only want to handle exclusive (`..`) ranges,
131 // which are represented as `ExprKind::Struct`.
132 let mut overwritten = false;
133 if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
137 // We can suggest using an inclusive range
138 // (`..=`) instead only if it is the `end` that is
139 // overflowing and only by 1.
140 if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
141 cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| {
142 let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty));
143 if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
144 use ast::{LitIntType, LitKind};
145 // We need to preserve the literal's suffix,
146 // as it may determine typing information.
147 let suffix = match lit.node {
148 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
149 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
150 LitKind::Int(_, LitIntType::Unsuffixed) => "",
153 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
156 &"use an inclusive range instead",
158 Applicability::MachineApplicable,
169 // For `isize` & `usize`, be conservative with the warnings, so that the
170 // warnings are consistent between 32- and 64-bit platforms.
171 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
173 ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
174 ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
175 ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
176 ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
177 ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
178 ty::IntTy::I128 => (i128::MIN, i128::MAX),
182 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
183 let max = match uint_ty {
184 ty::UintTy::Usize => u64::MAX.into(),
185 ty::UintTy::U8 => u8::MAX.into(),
186 ty::UintTy::U16 => u16::MAX.into(),
187 ty::UintTy::U32 => u32::MAX.into(),
188 ty::UintTy::U64 => u64::MAX.into(),
189 ty::UintTy::U128 => u128::MAX,
194 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
195 let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
196 let firstch = src.chars().next()?;
199 match src.chars().nth(1) {
200 Some('x' | 'b') => return Some(src),
208 fn report_bin_hex_error(
209 cx: &LateContext<'_>,
210 expr: &hir::Expr<'_>,
216 let size = Integer::from_attr(&cx.tcx, ty).size();
217 cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
218 let (t, actually) = match ty {
219 attr::IntType::SignedInt(t) => {
220 let actually = size.sign_extend(val) as i128;
221 (t.name_str(), actually.to_string())
223 attr::IntType::UnsignedInt(t) => {
224 let actually = size.truncate(val);
225 (t.name_str(), actually.to_string())
228 let mut err = lint.build(&format!("literal out of range for `{}`", t));
230 "the literal `{}` (decimal `{}`) does not fit into \
231 the type `{}` and will become `{}{}`",
232 repr_str, val, t, actually, t
234 if let Some(sugg_ty) =
235 get_type_suggestion(&cx.typeck_results().node_type(expr.hir_id), val, negative)
237 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
238 let (sans_suffix, _) = repr_str.split_at(pos);
241 &format!("consider using the type `{}` instead", sugg_ty),
242 format!("{}{}", sans_suffix, sugg_ty),
243 Applicability::MachineApplicable,
246 err.help(&format!("consider using the type `{}` instead", sugg_ty));
253 // This function finds the next fitting type and generates a suggestion string.
254 // It searches for fitting types in the following way (`X < Y`):
255 // - `iX`: if literal fits in `uX` => `uX`, else => `iY`
259 // No suggestion for: `isize`, `usize`.
260 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
263 macro_rules! find_fit {
264 ($ty:expr, $val:expr, $negative:expr,
265 $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
267 let _neg = if negative { 1 } else { 0 };
270 $(if !negative && val <= uint_ty_range($utypes).1 {
271 return Some($utypes.name_str())
273 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
274 return Some($itypes.name_str())
284 ty::Int(i) => find_fit!(i, val, negative,
285 I8 => [U8] => [I16, I32, I64, I128],
286 I16 => [U16] => [I32, I64, I128],
287 I32 => [U32] => [I64, I128],
288 I64 => [U64] => [I128],
289 I128 => [U128] => []),
290 ty::Uint(u) => find_fit!(u, val, negative,
291 U8 => [U8, U16, U32, U64, U128] => [],
292 U16 => [U16, U32, U64, U128] => [],
293 U32 => [U32, U64, U128] => [],
294 U64 => [U64, U128] => [],
295 U128 => [U128] => []),
300 fn lint_int_literal<'tcx>(
301 cx: &LateContext<'tcx>,
302 type_limits: &TypeLimits,
303 e: &'tcx hir::Expr<'tcx>,
308 let int_type = t.normalize(cx.sess().target.pointer_width);
309 let (min, max) = int_ty_range(int_type);
310 let max = max as u128;
311 let negative = type_limits.negated_expr_id == Some(e.hir_id);
313 // Detect literal value out of range [min, max] inclusive
314 // avoiding use of -min to prevent overflow/panic
315 if (negative && v > max + 1) || (!negative && v > max) {
316 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
317 report_bin_hex_error(
320 attr::IntType::SignedInt(ty::ast_int_ty(t)),
328 let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
329 if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
330 if let hir::ExprKind::Struct(..) = par_e.kind {
331 if is_range_literal(par_e)
332 && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
334 // The overflowing literal lint was overridden.
340 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
341 let mut err = lint.build(&format!("literal out of range for `{}`", t.name_str()));
343 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
346 .span_to_snippet(lit.span)
347 .expect("must get snippet from literal"),
352 if let Some(sugg_ty) =
353 get_type_suggestion(&cx.typeck_results().node_type(e.hir_id), v, negative)
355 err.help(&format!("consider using the type `{}` instead", sugg_ty));
362 fn lint_uint_literal<'tcx>(
363 cx: &LateContext<'tcx>,
364 e: &'tcx hir::Expr<'tcx>,
368 let uint_type = t.normalize(cx.sess().target.pointer_width);
369 let (min, max) = uint_ty_range(uint_type);
370 let lit_val: u128 = match lit.node {
371 // _v is u8, within range by definition
372 ast::LitKind::Byte(_v) => return,
373 ast::LitKind::Int(v, _) => v,
376 if lit_val < min || lit_val > max {
377 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
378 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
380 hir::ExprKind::Cast(..) => {
381 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
382 cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
383 lint.build("only `u8` can be cast into `char`")
386 &"use a `char` literal instead",
387 format!("'\\u{{{:X}}}'", lit_val),
388 Applicability::MachineApplicable,
395 hir::ExprKind::Struct(..) if is_range_literal(par_e) => {
396 let t = t.name_str();
397 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
398 // The overflowing literal lint was overridden.
405 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
406 report_bin_hex_error(
409 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
416 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
417 lint.build(&format!("literal out of range for `{}`", t.name_str()))
419 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
422 .span_to_snippet(lit.span)
423 .expect("must get snippet from literal"),
433 fn lint_literal<'tcx>(
434 cx: &LateContext<'tcx>,
435 type_limits: &TypeLimits,
436 e: &'tcx hir::Expr<'tcx>,
439 match *cx.typeck_results().node_type(e.hir_id).kind() {
442 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
443 lint_int_literal(cx, type_limits, e, lit, t, v)
448 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
450 let is_infinite = match lit.node {
451 ast::LitKind::Float(v, _) => match t {
452 ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
453 ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
457 if is_infinite == Ok(true) {
458 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
459 lint.build(&format!("literal out of range for `{}`", t.name_str()))
461 "the literal `{}` does not fit into the type `{}` and will be converted to `{}::INFINITY`",
464 .span_to_snippet(lit.span)
465 .expect("must get snippet from literal"),
477 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
478 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
480 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
481 // propagate negation, if the negation itself isn't negated
482 if self.negated_expr_id != Some(e.hir_id) {
483 self.negated_expr_id = Some(expr.hir_id);
486 hir::ExprKind::Binary(binop, ref l, ref r) => {
487 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
488 cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
489 lint.build("comparison is useless due to type limits").emit()
493 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
497 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
499 hir::BinOpKind::Lt => v > min && v <= max,
500 hir::BinOpKind::Le => v >= min && v < max,
501 hir::BinOpKind::Gt => v >= min && v < max,
502 hir::BinOpKind::Ge => v > min && v <= max,
503 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
508 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
512 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
513 hir::BinOpKind::Le => hir::BinOpKind::Ge,
514 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
515 hir::BinOpKind::Ge => hir::BinOpKind::Le,
522 cx: &LateContext<'_>,
527 let (lit, expr, swap) = match (&l.kind, &r.kind) {
528 (&hir::ExprKind::Lit(_), _) => (l, r, true),
529 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
532 // Normalize the binop so that the literal is always on the RHS in
534 let norm_binop = if swap { rev_binop(binop) } else { binop };
535 match *cx.typeck_results().node_type(expr.hir_id).kind() {
537 let (min, max) = int_ty_range(int_ty);
538 let lit_val: i128 = match lit.kind {
539 hir::ExprKind::Lit(ref li) => match li.node {
542 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
548 is_valid(norm_binop, lit_val, min, max)
550 ty::Uint(uint_ty) => {
551 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
552 let lit_val: u128 = match lit.kind {
553 hir::ExprKind::Lit(ref li) => match li.node {
554 ast::LitKind::Int(v, _) => v,
559 is_valid(norm_binop, lit_val, min, max)
565 fn is_comparison(binop: hir::BinOp) -> bool {
580 /// The `improper_ctypes` lint detects incorrect use of types in foreign
587 /// static STATIC: String;
595 /// The compiler has several checks to verify that types used in `extern`
596 /// blocks are safe and follow certain rules to ensure proper
597 /// compatibility with the foreign interfaces. This lint is issued when it
598 /// detects a probable mistake in a definition. The lint usually should
599 /// provide a description of the issue, along with possibly a hint on how
603 "proper use of libc types in foreign modules"
606 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
609 /// The `improper_ctypes_definitions` lint detects incorrect use of
610 /// [`extern` function] definitions.
612 /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
617 /// # #![allow(unused)]
618 /// pub extern "C" fn str_type(p: &str) { }
625 /// There are many parameter and return types that may be specified in an
626 /// `extern` function that are not compatible with the given ABI. This
627 /// lint is an alert that these types should not be used. The lint usually
628 /// should provide a description of the issue, along with possibly a hint
629 /// on how to resolve it.
630 IMPROPER_CTYPES_DEFINITIONS,
632 "proper use of libc types in foreign item definitions"
635 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
637 #[derive(Clone, Copy)]
638 crate enum CItemKind {
643 struct ImproperCTypesVisitor<'a, 'tcx> {
644 cx: &'a LateContext<'tcx>,
648 enum FfiResult<'tcx> {
650 FfiPhantom(Ty<'tcx>),
651 FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option<String> },
654 crate fn nonnull_optimization_guaranteed<'tcx>(tcx: TyCtxt<'tcx>, def: &ty::AdtDef) -> bool {
655 tcx.get_attrs(def.did)
657 .any(|a| tcx.sess.check_name(a, sym::rustc_nonnull_optimization_guaranteed))
660 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
662 pub fn transparent_newtype_field<'a, 'tcx>(
664 variant: &'a ty::VariantDef,
665 ) -> Option<&'a ty::FieldDef> {
666 let param_env = tcx.param_env(variant.def_id);
667 for field in &variant.fields {
668 let field_ty = tcx.type_of(field.did);
669 let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
679 /// Is type known to be non-null?
680 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
683 ty::FnPtr(_) => true,
685 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
686 ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
687 let marked_non_null = nonnull_optimization_guaranteed(tcx, &def);
693 // Types with a `#[repr(no_niche)]` attribute have their niche hidden.
694 // The attribute is used by the UnsafeCell for example (the only use so far).
695 if def.repr.hide_niche() {
699 for variant in &def.variants {
700 if let Some(field) = transparent_newtype_field(cx.tcx, variant) {
701 if ty_is_known_nonnull(cx, field.ty(tcx, substs), mode) {
713 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
714 /// If the type passed in was not scalar, returns None.
715 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
717 Some(match *ty.kind() {
718 ty::Adt(field_def, field_substs) => {
719 let inner_field_ty = {
720 let first_non_zst_ty =
721 field_def.variants.iter().filter_map(|v| transparent_newtype_field(cx.tcx, v));
723 first_non_zst_ty.clone().count(),
725 "Wrong number of fields for transparent type"
729 .expect("No non-zst fields in transparent type.")
730 .ty(tcx, field_substs)
732 return get_nullable_type(cx, inner_field_ty);
734 ty::Int(ty) => tcx.mk_mach_int(ty),
735 ty::Uint(ty) => tcx.mk_mach_uint(ty),
736 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
737 // As these types are always non-null, the nullable equivalent of
738 // Option<T> of these types are their raw pointer counterparts.
739 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
741 // There is no nullable equivalent for Rust's function pointers -- you
742 // must use an Option<fn(..) -> _> to represent it.
746 // We should only ever reach this case if ty_is_known_nonnull is extended
750 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
758 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
759 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
760 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
761 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
762 /// FIXME: This duplicates code in codegen.
763 crate fn repr_nullable_ptr<'tcx>(
764 cx: &LateContext<'tcx>,
767 ) -> Option<Ty<'tcx>> {
768 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
769 if let ty::Adt(ty_def, substs) = ty.kind() {
770 if ty_def.variants.len() != 2 {
774 let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
775 let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
776 let fields = if variant_fields[0].is_empty() {
778 } else if variant_fields[1].is_empty() {
784 if fields.len() != 1 {
788 let field_ty = fields[0].ty(cx.tcx, substs);
789 if !ty_is_known_nonnull(cx, field_ty, ckind) {
793 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
794 // If the computed size for the field and the enum are different, the nonnull optimization isn't
795 // being applied (and we've got a problem somewhere).
796 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
797 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
798 bug!("improper_ctypes: Option nonnull optimization not applied?");
801 // Return the nullable type this Option-like enum can be safely represented with.
802 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
803 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
804 match (field_ty_scalar.valid_range.start(), field_ty_scalar.valid_range.end()) {
805 (0, _) => unreachable!("Non-null optimisation extended to a non-zero value."),
807 return Some(get_nullable_type(cx, field_ty).unwrap());
809 (start, end) => unreachable!("Unhandled start and end range: ({}, {})", start, end),
816 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
817 /// Check if the type is array and emit an unsafe type lint.
818 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
819 if let ty::Array(..) = ty.kind() {
820 self.emit_ffi_unsafe_type_lint(
823 "passing raw arrays by value is not FFI-safe",
824 Some("consider passing a pointer to the array"),
832 /// Checks if the given field's type is "ffi-safe".
833 fn check_field_type_for_ffi(
835 cache: &mut FxHashSet<Ty<'tcx>>,
836 field: &ty::FieldDef,
837 substs: SubstsRef<'tcx>,
838 ) -> FfiResult<'tcx> {
839 let field_ty = field.ty(self.cx.tcx, substs);
840 if field_ty.has_opaque_types() {
841 self.check_type_for_ffi(cache, field_ty)
843 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
844 self.check_type_for_ffi(cache, field_ty)
848 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
849 fn check_variant_for_ffi(
851 cache: &mut FxHashSet<Ty<'tcx>>,
854 variant: &ty::VariantDef,
855 substs: SubstsRef<'tcx>,
856 ) -> FfiResult<'tcx> {
859 if def.repr.transparent() {
860 // Can assume that only one field is not a ZST, so only check
861 // that field's type for FFI-safety.
862 if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
863 self.check_field_type_for_ffi(cache, field, substs)
865 bug!("malformed transparent type");
868 // We can't completely trust repr(C) markings; make sure the fields are
870 let mut all_phantom = !variant.fields.is_empty();
871 for field in &variant.fields {
872 match self.check_field_type_for_ffi(cache, &field, substs) {
876 FfiPhantom(..) if def.is_enum() => {
879 reason: "this enum contains a PhantomData field".into(),
888 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
892 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
893 /// representation which can be exported to C code).
894 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
897 let tcx = self.cx.tcx;
899 // Protect against infinite recursion, for example
900 // `struct S(*mut S);`.
901 // FIXME: A recursion limit is necessary as well, for irregular
903 if !cache.insert(ty) {
908 ty::Adt(def, _) if def.is_box() && matches!(self.mode, CItemKind::Definition) => {
912 ty::Adt(def, substs) => {
913 if def.is_phantom_data() {
914 return FfiPhantom(ty);
916 match def.adt_kind() {
917 AdtKind::Struct | AdtKind::Union => {
918 let kind = if def.is_struct() { "struct" } else { "union" };
920 if !def.repr.c() && !def.repr.transparent() {
923 reason: format!("this {} has unspecified layout", kind),
925 "consider adding a `#[repr(C)]` or \
926 `#[repr(transparent)]` attribute to this {}",
932 let is_non_exhaustive =
933 def.non_enum_variant().is_field_list_non_exhaustive();
934 if is_non_exhaustive && !def.did.is_local() {
937 reason: format!("this {} is non-exhaustive", kind),
942 if def.non_enum_variant().fields.is_empty() {
945 reason: format!("this {} has no fields", kind),
946 help: Some(format!("consider adding a member to this {}", kind)),
950 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
953 if def.variants.is_empty() {
954 // Empty enums are okay... although sort of useless.
958 // Check for a repr() attribute to specify the size of the
960 if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
961 // Special-case types like `Option<extern fn()>`.
962 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
965 reason: "enum has no representation hint".into(),
967 "consider adding a `#[repr(C)]`, \
968 `#[repr(transparent)]`, or integer `#[repr(...)]` \
969 attribute to this enum"
976 if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
979 reason: "this enum is non-exhaustive".into(),
984 // Check the contained variants.
985 for variant in &def.variants {
986 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
987 if is_non_exhaustive && !variant.def_id.is_local() {
990 reason: "this enum has non-exhaustive variants".into(),
995 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1006 ty::Char => FfiUnsafe {
1008 reason: "the `char` type has no C equivalent".into(),
1009 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
1012 ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => FfiUnsafe {
1014 reason: "128-bit integers don't currently have a known stable ABI".into(),
1018 // Primitive types with a stable representation.
1019 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1021 ty::Slice(_) => FfiUnsafe {
1023 reason: "slices have no C equivalent".into(),
1024 help: Some("consider using a raw pointer instead".into()),
1027 ty::Dynamic(..) => {
1028 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
1031 ty::Str => FfiUnsafe {
1033 reason: "string slices have no C equivalent".into(),
1034 help: Some("consider using `*const u8` and a length instead".into()),
1037 ty::Tuple(..) => FfiUnsafe {
1039 reason: "tuples have unspecified layout".into(),
1040 help: Some("consider using a struct instead".into()),
1043 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1045 matches!(self.mode, CItemKind::Definition)
1046 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1052 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1053 self.check_type_for_ffi(cache, ty)
1056 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1059 if self.is_internal_abi(sig.abi()) {
1062 reason: "this function pointer has Rust-specific calling convention".into(),
1064 "consider using an `extern fn(...) -> ...` \
1065 function pointer instead"
1071 let sig = tcx.erase_late_bound_regions(sig);
1072 if !sig.output().is_unit() {
1073 let r = self.check_type_for_ffi(cache, sig.output());
1081 for arg in sig.inputs() {
1082 let r = self.check_type_for_ffi(cache, arg);
1093 ty::Foreign(..) => FfiSafe,
1095 // While opaque types are checked for earlier, if a projection in a struct field
1096 // normalizes to an opaque type, then it will reach this branch.
1098 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
1101 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1102 // so they are currently ignored for the purposes of this lint.
1103 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1108 | ty::Projection(..)
1114 | ty::GeneratorWitness(..)
1115 | ty::Placeholder(..)
1116 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1120 fn emit_ffi_unsafe_type_lint(
1127 let lint = match self.mode {
1128 CItemKind::Declaration => IMPROPER_CTYPES,
1129 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1132 self.cx.struct_span_lint(lint, sp, |lint| {
1133 let item_description = match self.mode {
1134 CItemKind::Declaration => "block",
1135 CItemKind::Definition => "fn",
1137 let mut diag = lint.build(&format!(
1138 "`extern` {} uses type `{}`, which is not FFI-safe",
1139 item_description, ty
1141 diag.span_label(sp, "not FFI-safe");
1142 if let Some(help) = help {
1146 if let ty::Adt(def, _) = ty.kind() {
1147 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
1148 diag.span_note(sp, "the type is defined here");
1155 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1156 struct ProhibitOpaqueTypes<'a, 'tcx> {
1157 cx: &'a LateContext<'tcx>,
1160 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1161 type BreakTy = Ty<'tcx>;
1163 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1165 ty::Opaque(..) => ControlFlow::Break(ty),
1166 // Consider opaque types within projections FFI-safe if they do not normalize
1167 // to more opaque types.
1168 ty::Projection(..) => {
1169 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1171 // If `ty` is a opaque type directly then `super_visit_with` won't invoke
1172 // this function again.
1173 if ty.has_opaque_types() {
1176 ControlFlow::CONTINUE
1179 _ => ty.super_visit_with(self),
1184 if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1185 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
1192 fn check_type_for_ffi_and_report_errors(
1197 is_return_type: bool,
1199 // We have to check for opaque types before `normalize_erasing_regions`,
1200 // which will replace opaque types with their underlying concrete type.
1201 if self.check_for_opaque_ty(sp, ty) {
1202 // We've already emitted an error due to an opaque type.
1206 // it is only OK to use this function because extern fns cannot have
1207 // any generic types right now:
1208 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1210 // C doesn't really support passing arrays by value - the only way to pass an array by value
1211 // is through a struct. So, first test that the top level isn't an array, and then
1212 // recursively check the types inside.
1213 if !is_static && self.check_for_array_ty(sp, ty) {
1217 // Don't report FFI errors for unit return types. This check exists here, and not in
1218 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1220 if is_return_type && ty.is_unit() {
1224 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1225 FfiResult::FfiSafe => {}
1226 FfiResult::FfiPhantom(ty) => {
1227 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1229 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1230 // argument, which after substitution, is `()`, then this branch can be hit.
1231 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1232 FfiResult::FfiUnsafe { ty, reason, help } => {
1233 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1238 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1239 let def_id = self.cx.tcx.hir().local_def_id(id);
1240 let sig = self.cx.tcx.fn_sig(def_id);
1241 let sig = self.cx.tcx.erase_late_bound_regions(sig);
1243 for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
1244 self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false);
1247 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1248 let ret_ty = sig.output();
1249 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1253 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1254 let def_id = self.cx.tcx.hir().local_def_id(id);
1255 let ty = self.cx.tcx.type_of(def_id);
1256 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1259 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1262 SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1267 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1268 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1269 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1270 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1272 if !vis.is_internal_abi(abi) {
1274 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1275 vis.check_foreign_fn(it.hir_id(), decl);
1277 hir::ForeignItemKind::Static(ref ty, _) => {
1278 vis.check_foreign_static(it.hir_id(), ty.span);
1280 hir::ForeignItemKind::Type => (),
1286 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1289 cx: &LateContext<'tcx>,
1290 kind: hir::intravisit::FnKind<'tcx>,
1291 decl: &'tcx hir::FnDecl<'_>,
1292 _: &'tcx hir::Body<'_>,
1296 use hir::intravisit::FnKind;
1298 let abi = match kind {
1299 FnKind::ItemFn(_, _, header, ..) => header.abi,
1300 FnKind::Method(_, sig, ..) => sig.header.abi,
1304 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1305 if !vis.is_internal_abi(abi) {
1306 vis.check_foreign_fn(hir_id, decl);
1311 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1313 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1314 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1315 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1316 let t = cx.tcx.type_of(it.def_id);
1317 let ty = cx.tcx.erase_regions(t);
1318 let layout = match cx.layout_of(ty) {
1319 Ok(layout) => layout,
1321 ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
1324 let (variants, tag) = match layout.variants {
1325 Variants::Multiple {
1326 tag_encoding: TagEncoding::Direct,
1330 } => (variants, tag),
1334 let tag_size = tag.value.size(&cx.tcx).bytes();
1337 "enum `{}` is {} bytes large with layout:\n{:#?}",
1339 layout.size.bytes(),
1343 let (largest, slargest, largest_index) = enum_definition
1347 .map(|(variant, variant_layout)| {
1348 // Subtract the size of the enum tag.
1349 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1351 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1355 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1358 } else if size > s {
1365 // We only warn if the largest variant is at least thrice as large as
1366 // the second-largest.
1367 if largest > slargest * 3 && slargest > 0 {
1368 cx.struct_span_lint(
1369 VARIANT_SIZE_DIFFERENCES,
1370 enum_definition.variants[largest_index].span,
1372 lint.build(&format!(
1373 "enum variant is more than three times \
1374 larger ({} bytes) than the next largest",