1 #![allow(non_snake_case)]
3 use crate::{LateContext, LateLintPass, LintContext};
5 use rustc_attr as attr;
6 use rustc_data_structures::fx::FxHashSet;
7 use rustc_errors::Applicability;
9 use rustc_hir::{is_range_literal, ExprKind, Node};
10 use rustc_index::vec::Idx;
11 use rustc_middle::mir::interpret::{sign_extend, truncate};
12 use rustc_middle::ty::layout::{IntegerExt, SizeSkeleton};
13 use rustc_middle::ty::subst::SubstsRef;
14 use rustc_middle::ty::{self, AdtKind, Ty, TyCtxt, TypeFoldable};
15 use rustc_span::source_map;
16 use rustc_span::symbol::sym;
17 use rustc_span::{Span, DUMMY_SP};
18 use rustc_target::abi::Abi;
19 use rustc_target::abi::{Integer, LayoutOf, TagEncoding, VariantIdx, Variants};
20 use rustc_target::spec::abi::Abi as SpecAbi;
28 "comparisons made useless by limits of the types involved"
34 "literal out of range for its type"
38 VARIANT_SIZE_DIFFERENCES,
40 "detects enums with widely varying variant sizes"
43 #[derive(Copy, Clone)]
44 pub struct TypeLimits {
45 /// Id of the last visited negated expression
46 negated_expr_id: Option<hir::HirId>,
49 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
52 pub fn new() -> TypeLimits {
53 TypeLimits { negated_expr_id: None }
57 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
58 /// Returns `true` iff the lint was overridden.
59 fn lint_overflowing_range_endpoint<'tcx>(
60 cx: &LateContext<'tcx>,
64 expr: &'tcx hir::Expr<'tcx>,
65 parent_expr: &'tcx hir::Expr<'tcx>,
68 // We only want to handle exclusive (`..`) ranges,
69 // which are represented as `ExprKind::Struct`.
70 let mut overwritten = false;
71 if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
75 // We can suggest using an inclusive range
76 // (`..=`) instead only if it is the `end` that is
77 // overflowing and only by 1.
78 if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
79 cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| {
80 let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty));
81 if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
82 use ast::{LitIntType, LitKind};
83 // We need to preserve the literal's suffix,
84 // as it may determine typing information.
85 let suffix = match lit.node {
86 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str().to_string(),
87 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str().to_string(),
88 LitKind::Int(_, LitIntType::Unsuffixed) => "".to_string(),
91 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
94 &"use an inclusive range instead",
96 Applicability::MachineApplicable,
107 // For `isize` & `usize`, be conservative with the warnings, so that the
108 // warnings are consistent between 32- and 64-bit platforms.
109 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
111 ast::IntTy::Isize => (i64::MIN as i128, i64::MAX as i128),
112 ast::IntTy::I8 => (i8::MIN as i64 as i128, i8::MAX as i128),
113 ast::IntTy::I16 => (i16::MIN as i64 as i128, i16::MAX as i128),
114 ast::IntTy::I32 => (i32::MIN as i64 as i128, i32::MAX as i128),
115 ast::IntTy::I64 => (i64::MIN as i128, i64::MAX as i128),
116 ast::IntTy::I128 => (i128::MIN as i128, i128::MAX),
120 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
122 ast::UintTy::Usize => (u64::MIN as u128, u64::MAX as u128),
123 ast::UintTy::U8 => (u8::MIN as u128, u8::MAX as u128),
124 ast::UintTy::U16 => (u16::MIN as u128, u16::MAX as u128),
125 ast::UintTy::U32 => (u32::MIN as u128, u32::MAX as u128),
126 ast::UintTy::U64 => (u64::MIN as u128, u64::MAX as u128),
127 ast::UintTy::U128 => (u128::MIN, u128::MAX),
131 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
132 let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
133 let firstch = src.chars().next()?;
136 match src.chars().nth(1) {
137 Some('x' | 'b') => return Some(src),
145 fn report_bin_hex_error(
146 cx: &LateContext<'_>,
147 expr: &hir::Expr<'_>,
153 let size = Integer::from_attr(&cx.tcx, ty).size();
154 cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
155 let (t, actually) = match ty {
156 attr::IntType::SignedInt(t) => {
157 let actually = sign_extend(val, size) as i128;
158 (t.name_str(), actually.to_string())
160 attr::IntType::UnsignedInt(t) => {
161 let actually = truncate(val, size);
162 (t.name_str(), actually.to_string())
165 let mut err = lint.build(&format!("literal out of range for {}", t));
167 "the literal `{}` (decimal `{}`) does not fit into \
168 the type `{}` and will become `{}{}`",
169 repr_str, val, t, actually, t
171 if let Some(sugg_ty) =
172 get_type_suggestion(&cx.typeck_results().node_type(expr.hir_id), val, negative)
174 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
175 let (sans_suffix, _) = repr_str.split_at(pos);
178 &format!("consider using `{}` instead", sugg_ty),
179 format!("{}{}", sans_suffix, sugg_ty),
180 Applicability::MachineApplicable,
183 err.help(&format!("consider using `{}` instead", sugg_ty));
190 // This function finds the next fitting type and generates a suggestion string.
191 // It searches for fitting types in the following way (`X < Y`):
192 // - `iX`: if literal fits in `uX` => `uX`, else => `iY`
196 // No suggestion for: `isize`, `usize`.
197 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
198 use rustc_ast::ast::IntTy::*;
199 use rustc_ast::ast::UintTy::*;
200 macro_rules! find_fit {
201 ($ty:expr, $val:expr, $negative:expr,
202 $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
204 let _neg = if negative { 1 } else { 0 };
207 $(if !negative && val <= uint_ty_range($utypes).1 {
208 return Some($utypes.name_str())
210 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
211 return Some($itypes.name_str())
221 ty::Int(i) => find_fit!(i, val, negative,
222 I8 => [U8] => [I16, I32, I64, I128],
223 I16 => [U16] => [I32, I64, I128],
224 I32 => [U32] => [I64, I128],
225 I64 => [U64] => [I128],
226 I128 => [U128] => []),
227 ty::Uint(u) => find_fit!(u, val, negative,
228 U8 => [U8, U16, U32, U64, U128] => [],
229 U16 => [U16, U32, U64, U128] => [],
230 U32 => [U32, U64, U128] => [],
231 U64 => [U64, U128] => [],
232 U128 => [U128] => []),
237 fn lint_int_literal<'tcx>(
238 cx: &LateContext<'tcx>,
239 type_limits: &TypeLimits,
240 e: &'tcx hir::Expr<'tcx>,
245 let int_type = t.normalize(cx.sess().target.ptr_width);
246 let (min, max) = int_ty_range(int_type);
247 let max = max as u128;
248 let negative = type_limits.negated_expr_id == Some(e.hir_id);
250 // Detect literal value out of range [min, max] inclusive
251 // avoiding use of -min to prevent overflow/panic
252 if (negative && v > max + 1) || (!negative && v > max) {
253 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
254 report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
258 let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
259 if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
260 if let hir::ExprKind::Struct(..) = par_e.kind {
261 if is_range_literal(cx.sess().source_map(), par_e)
262 && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
264 // The overflowing literal lint was overridden.
270 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
271 lint.build(&format!("literal out of range for `{}`", t.name_str()))
273 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
276 .span_to_snippet(lit.span)
277 .expect("must get snippet from literal"),
287 fn lint_uint_literal<'tcx>(
288 cx: &LateContext<'tcx>,
289 e: &'tcx hir::Expr<'tcx>,
293 let uint_type = t.normalize(cx.sess().target.ptr_width);
294 let (min, max) = uint_ty_range(uint_type);
295 let lit_val: u128 = match lit.node {
296 // _v is u8, within range by definition
297 ast::LitKind::Byte(_v) => return,
298 ast::LitKind::Int(v, _) => v,
301 if lit_val < min || lit_val > max {
302 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
303 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
305 hir::ExprKind::Cast(..) => {
306 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind {
307 cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
308 lint.build("only `u8` can be cast into `char`")
311 &"use a `char` literal instead",
312 format!("'\\u{{{:X}}}'", lit_val),
313 Applicability::MachineApplicable,
320 hir::ExprKind::Struct(..) if is_range_literal(cx.sess().source_map(), par_e) => {
321 let t = t.name_str();
322 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
323 // The overflowing literal lint was overridden.
330 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
331 report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
334 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
335 lint.build(&format!("literal out of range for `{}`", t.name_str()))
337 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
340 .span_to_snippet(lit.span)
341 .expect("must get snippet from literal"),
351 fn lint_literal<'tcx>(
352 cx: &LateContext<'tcx>,
353 type_limits: &TypeLimits,
354 e: &'tcx hir::Expr<'tcx>,
357 match cx.typeck_results().node_type(e.hir_id).kind {
360 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
361 lint_int_literal(cx, type_limits, e, lit, t, v)
366 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
368 let is_infinite = match lit.node {
369 ast::LitKind::Float(v, _) => match t {
370 ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
371 ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
375 if is_infinite == Ok(true) {
376 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
377 lint.build(&format!("literal out of range for `{}`", t.name_str()))
379 "the literal `{}` does not fit into the type `{}` and will be converted to `std::{}::INFINITY`",
382 .span_to_snippet(lit.span)
383 .expect("must get snippet from literal"),
395 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
396 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
398 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
399 // propagate negation, if the negation itself isn't negated
400 if self.negated_expr_id != Some(e.hir_id) {
401 self.negated_expr_id = Some(expr.hir_id);
404 hir::ExprKind::Binary(binop, ref l, ref r) => {
405 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
406 cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
407 lint.build("comparison is useless due to type limits").emit()
411 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
415 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
417 hir::BinOpKind::Lt => v > min && v <= max,
418 hir::BinOpKind::Le => v >= min && v < max,
419 hir::BinOpKind::Gt => v >= min && v < max,
420 hir::BinOpKind::Ge => v > min && v <= max,
421 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
426 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
430 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
431 hir::BinOpKind::Le => hir::BinOpKind::Ge,
432 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
433 hir::BinOpKind::Ge => hir::BinOpKind::Le,
440 cx: &LateContext<'_>,
445 let (lit, expr, swap) = match (&l.kind, &r.kind) {
446 (&hir::ExprKind::Lit(_), _) => (l, r, true),
447 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
450 // Normalize the binop so that the literal is always on the RHS in
452 let norm_binop = if swap { rev_binop(binop) } else { binop };
453 match cx.typeck_results().node_type(expr.hir_id).kind {
455 let (min, max) = int_ty_range(int_ty);
456 let lit_val: i128 = match lit.kind {
457 hir::ExprKind::Lit(ref li) => match li.node {
460 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
466 is_valid(norm_binop, lit_val, min, max)
468 ty::Uint(uint_ty) => {
469 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
470 let lit_val: u128 = match lit.kind {
471 hir::ExprKind::Lit(ref li) => match li.node {
472 ast::LitKind::Int(v, _) => v,
477 is_valid(norm_binop, lit_val, min, max)
483 fn is_comparison(binop: hir::BinOp) -> bool {
490 | hir::BinOpKind::Gt => true,
500 "proper use of libc types in foreign modules"
503 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
506 IMPROPER_CTYPES_DEFINITIONS,
508 "proper use of libc types in foreign item definitions"
511 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
513 #[derive(Clone, Copy)]
514 crate enum CItemKind {
519 struct ImproperCTypesVisitor<'a, 'tcx> {
520 cx: &'a LateContext<'tcx>,
524 enum FfiResult<'tcx> {
526 FfiPhantom(Ty<'tcx>),
527 FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option<String> },
530 /// Is type known to be non-null?
531 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
534 ty::FnPtr(_) => true,
536 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
537 ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
538 let guaranteed_nonnull_optimization = tcx
541 .any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed));
543 if guaranteed_nonnull_optimization {
546 for variant in &def.variants {
547 if let Some(field) = variant.transparent_newtype_field(tcx) {
548 if ty_is_known_nonnull(cx, field.ty(tcx, substs), mode) {
559 /// Given a potentially non-null type `ty`, return its default, nullable type.
560 fn get_nullable_type<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
562 ty::Adt(field_def, field_substs) => {
563 let field_variants = &field_def.variants;
564 // We hit this case for #[repr(transparent)] structs with a single
567 field_variants.len() == 1 && field_variants[VariantIdx::new(0)].fields.len() == 1,
568 "inner ty not a newtype struct"
570 debug_assert!(field_def.repr.transparent(), "inner ty not transparent");
571 // As it's easy to get this wrong, it's worth noting that
572 // `inner_field_ty` is not the same as `field_ty`: Given Option<S>,
573 // where S is a transparent newtype of some type T, `field_ty`
574 // gives us S, while `inner_field_ty` is T.
576 field_def.variants[VariantIdx::new(0)].fields[0].ty(tcx, field_substs);
577 get_nullable_type(tcx, inner_field_ty)
579 ty::Int(ty) => tcx.mk_mach_int(ty),
580 ty::Uint(ty) => tcx.mk_mach_uint(ty),
581 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
582 // As these types are always non-null, the nullable equivalent of
583 // Option<T> of these types are their raw pointer counterparts.
584 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
586 // There is no nullable equivalent for Rust's function pointers -- you
587 // must use an Option<fn(..) -> _> to represent it.
591 // We should only ever reach this case if ty_is_known_nonnull is extended
594 unreachable!("Unhandled scalar kind: {:?} while checking {:?}", unhandled, ty)
599 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
600 /// can, return the the type that `ty` can be safely converted to, otherwise return `None`.
601 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
602 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
603 /// FIXME: This duplicates code in codegen.
604 crate fn repr_nullable_ptr<'tcx>(
605 cx: &LateContext<'tcx>,
608 ) -> Option<Ty<'tcx>> {
609 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
610 if let ty::Adt(ty_def, substs) = ty.kind {
611 if ty_def.variants.len() != 2 {
615 let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
616 let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
617 let fields = if variant_fields[0].is_empty() {
619 } else if variant_fields[1].is_empty() {
625 if fields.len() != 1 {
629 let field_ty = fields[0].ty(cx.tcx, substs);
630 if !ty_is_known_nonnull(cx, field_ty, ckind) {
634 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
635 // If the computed size for the field and the enum are different, the nonnull optimization isn't
636 // being applied (and we've got a problem somewhere).
637 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
638 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
639 bug!("improper_ctypes: Option nonnull optimization not applied?");
642 // Return the nullable type this Option-like enum can be safely represented with.
643 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
644 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
645 match (field_ty_scalar.valid_range.start(), field_ty_scalar.valid_range.end()) {
646 (0, _) => bug!("Non-null optimisation extended to a non-zero value."),
648 return Some(get_nullable_type(cx.tcx, field_ty));
650 (start, end) => unreachable!("Unhandled start and end range: ({}, {})", start, end),
657 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
658 /// Check if the type is array and emit an unsafe type lint.
659 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
660 if let ty::Array(..) = ty.kind {
661 self.emit_ffi_unsafe_type_lint(
664 "passing raw arrays by value is not FFI-safe",
665 Some("consider passing a pointer to the array"),
673 /// Checks if the given field's type is "ffi-safe".
674 fn check_field_type_for_ffi(
676 cache: &mut FxHashSet<Ty<'tcx>>,
677 field: &ty::FieldDef,
678 substs: SubstsRef<'tcx>,
679 ) -> FfiResult<'tcx> {
680 let field_ty = field.ty(self.cx.tcx, substs);
681 if field_ty.has_opaque_types() {
682 self.check_type_for_ffi(cache, field_ty)
684 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
685 self.check_type_for_ffi(cache, field_ty)
689 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
690 fn check_variant_for_ffi(
692 cache: &mut FxHashSet<Ty<'tcx>>,
695 variant: &ty::VariantDef,
696 substs: SubstsRef<'tcx>,
697 ) -> FfiResult<'tcx> {
700 if def.repr.transparent() {
701 // Can assume that only one field is not a ZST, so only check
702 // that field's type for FFI-safety.
703 if let Some(field) = variant.transparent_newtype_field(self.cx.tcx) {
704 self.check_field_type_for_ffi(cache, field, substs)
706 bug!("malformed transparent type");
709 // We can't completely trust repr(C) markings; make sure the fields are
711 let mut all_phantom = !variant.fields.is_empty();
712 for field in &variant.fields {
713 match self.check_field_type_for_ffi(cache, &field, substs) {
717 FfiPhantom(..) if def.is_enum() => {
720 reason: "this enum contains a PhantomData field".into(),
729 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
733 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
734 /// representation which can be exported to C code).
735 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
738 let tcx = self.cx.tcx;
740 // Protect against infinite recursion, for example
741 // `struct S(*mut S);`.
742 // FIXME: A recursion limit is necessary as well, for irregular
744 if !cache.insert(ty) {
749 ty::Adt(def, _) if def.is_box() && matches!(self.mode, CItemKind::Definition) => {
753 ty::Adt(def, substs) => {
754 if def.is_phantom_data() {
755 return FfiPhantom(ty);
757 match def.adt_kind() {
758 AdtKind::Struct | AdtKind::Union => {
759 let kind = if def.is_struct() { "struct" } else { "union" };
761 if !def.repr.c() && !def.repr.transparent() {
764 reason: format!("this {} has unspecified layout", kind),
766 "consider adding a `#[repr(C)]` or \
767 `#[repr(transparent)]` attribute to this {}",
773 let is_non_exhaustive =
774 def.non_enum_variant().is_field_list_non_exhaustive();
775 if is_non_exhaustive && !def.did.is_local() {
778 reason: format!("this {} is non-exhaustive", kind),
783 if def.non_enum_variant().fields.is_empty() {
786 reason: format!("this {} has no fields", kind),
787 help: Some(format!("consider adding a member to this {}", kind)),
791 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
794 if def.variants.is_empty() {
795 // Empty enums are okay... although sort of useless.
799 // Check for a repr() attribute to specify the size of the
801 if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
802 // Special-case types like `Option<extern fn()>`.
803 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
806 reason: "enum has no representation hint".into(),
808 "consider adding a `#[repr(C)]`, \
809 `#[repr(transparent)]`, or integer `#[repr(...)]` \
810 attribute to this enum"
817 if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
820 reason: "this enum is non-exhaustive".into(),
825 // Check the contained variants.
826 for variant in &def.variants {
827 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
828 if is_non_exhaustive && !variant.def_id.is_local() {
831 reason: "this enum has non-exhaustive variants".into(),
836 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
847 ty::Char => FfiUnsafe {
849 reason: "the `char` type has no C equivalent".into(),
850 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
853 ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
855 reason: "128-bit integers don't currently have a known stable ABI".into(),
859 // Primitive types with a stable representation.
860 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
862 ty::Slice(_) => FfiUnsafe {
864 reason: "slices have no C equivalent".into(),
865 help: Some("consider using a raw pointer instead".into()),
869 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
872 ty::Str => FfiUnsafe {
874 reason: "string slices have no C equivalent".into(),
875 help: Some("consider using `*const u8` and a length instead".into()),
878 ty::Tuple(..) => FfiUnsafe {
880 reason: "tuples have unspecified layout".into(),
881 help: Some("consider using a struct instead".into()),
884 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
886 matches!(self.mode, CItemKind::Definition)
887 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
893 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
894 self.check_type_for_ffi(cache, ty)
897 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
900 if self.is_internal_abi(sig.abi()) {
903 reason: "this function pointer has Rust-specific calling convention".into(),
905 "consider using an `extern fn(...) -> ...` \
906 function pointer instead"
912 let sig = tcx.erase_late_bound_regions(&sig);
913 if !sig.output().is_unit() {
914 let r = self.check_type_for_ffi(cache, sig.output());
922 for arg in sig.inputs() {
923 let r = self.check_type_for_ffi(cache, arg);
934 ty::Foreign(..) => FfiSafe,
936 // While opaque types are checked for earlier, if a projection in a struct field
937 // normalizes to an opaque type, then it will reach this branch.
939 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
942 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
943 // so they are currently ignored for the purposes of this lint.
944 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
955 | ty::GeneratorWitness(..)
956 | ty::Placeholder(..)
957 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
961 fn emit_ffi_unsafe_type_lint(
968 let lint = match self.mode {
969 CItemKind::Declaration => IMPROPER_CTYPES,
970 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
973 self.cx.struct_span_lint(lint, sp, |lint| {
974 let item_description = match self.mode {
975 CItemKind::Declaration => "block",
976 CItemKind::Definition => "fn",
978 let mut diag = lint.build(&format!(
979 "`extern` {} uses type `{}`, which is not FFI-safe",
982 diag.span_label(sp, "not FFI-safe");
983 if let Some(help) = help {
987 if let ty::Adt(def, _) = ty.kind {
988 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
989 diag.span_note(sp, "the type is defined here");
996 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
997 struct ProhibitOpaqueTypes<'a, 'tcx> {
998 cx: &'a LateContext<'tcx>,
999 ty: Option<Ty<'tcx>>,
1002 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1003 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
1009 // Consider opaque types within projections FFI-safe if they do not normalize
1010 // to more opaque types.
1011 ty::Projection(..) => {
1012 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1014 // If `ty` is a opaque type directly then `super_visit_with` won't invoke
1015 // this function again.
1016 if ty.has_opaque_types() { self.visit_ty(ty) } else { false }
1018 _ => ty.super_visit_with(self),
1023 let mut visitor = ProhibitOpaqueTypes { cx: self.cx, ty: None };
1024 ty.visit_with(&mut visitor);
1025 if let Some(ty) = visitor.ty {
1026 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
1033 fn check_type_for_ffi_and_report_errors(
1038 is_return_type: bool,
1040 // We have to check for opaque types before `normalize_erasing_regions`,
1041 // which will replace opaque types with their underlying concrete type.
1042 if self.check_for_opaque_ty(sp, ty) {
1043 // We've already emitted an error due to an opaque type.
1047 // it is only OK to use this function because extern fns cannot have
1048 // any generic types right now:
1049 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1051 // C doesn't really support passing arrays by value - the only way to pass an array by value
1052 // is through a struct. So, first test that the top level isn't an array, and then
1053 // recursively check the types inside.
1054 if !is_static && self.check_for_array_ty(sp, ty) {
1058 // Don't report FFI errors for unit return types. This check exists here, and not in
1059 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1061 if is_return_type && ty.is_unit() {
1065 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1066 FfiResult::FfiSafe => {}
1067 FfiResult::FfiPhantom(ty) => {
1068 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1070 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1071 // argument, which after substitution, is `()`, then this branch can be hit.
1072 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => return,
1073 FfiResult::FfiUnsafe { ty, reason, help } => {
1074 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1079 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1080 let def_id = self.cx.tcx.hir().local_def_id(id);
1081 let sig = self.cx.tcx.fn_sig(def_id);
1082 let sig = self.cx.tcx.erase_late_bound_regions(&sig);
1084 for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
1085 self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false);
1088 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1089 let ret_ty = sig.output();
1090 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1094 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1095 let def_id = self.cx.tcx.hir().local_def_id(id);
1096 let ty = self.cx.tcx.type_of(def_id);
1097 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1100 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1101 if let SpecAbi::Rust
1103 | SpecAbi::RustIntrinsic
1104 | SpecAbi::PlatformIntrinsic = abi
1113 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1114 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1115 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1116 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
1118 if !vis.is_internal_abi(abi) {
1120 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1121 vis.check_foreign_fn(it.hir_id, decl);
1123 hir::ForeignItemKind::Static(ref ty, _) => {
1124 vis.check_foreign_static(it.hir_id, ty.span);
1126 hir::ForeignItemKind::Type => (),
1132 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1135 cx: &LateContext<'tcx>,
1136 kind: hir::intravisit::FnKind<'tcx>,
1137 decl: &'tcx hir::FnDecl<'_>,
1138 _: &'tcx hir::Body<'_>,
1142 use hir::intravisit::FnKind;
1144 let abi = match kind {
1145 FnKind::ItemFn(_, _, header, ..) => header.abi,
1146 FnKind::Method(_, sig, ..) => sig.header.abi,
1150 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1151 if !vis.is_internal_abi(abi) {
1152 vis.check_foreign_fn(hir_id, decl);
1157 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1159 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1160 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1161 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1162 let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1163 let t = cx.tcx.type_of(item_def_id);
1164 let ty = cx.tcx.erase_regions(&t);
1165 let layout = match cx.layout_of(ty) {
1166 Ok(layout) => layout,
1168 ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
1171 let (variants, tag) = match layout.variants {
1172 Variants::Multiple {
1173 tag_encoding: TagEncoding::Direct,
1177 } => (variants, tag),
1181 let tag_size = tag.value.size(&cx.tcx).bytes();
1184 "enum `{}` is {} bytes large with layout:\n{:#?}",
1186 layout.size.bytes(),
1190 let (largest, slargest, largest_index) = enum_definition
1194 .map(|(variant, variant_layout)| {
1195 // Subtract the size of the enum tag.
1196 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1198 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1202 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1205 } else if size > s {
1212 // We only warn if the largest variant is at least thrice as large as
1213 // the second-largest.
1214 if largest > slargest * 3 && slargest > 0 {
1215 cx.struct_span_lint(
1216 VARIANT_SIZE_DIFFERENCES,
1217 enum_definition.variants[largest_index].span,
1219 lint.build(&format!(
1220 "enum variant is more than three times \
1221 larger ({} bytes) than the next largest",