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 = if negative {
221 -(size.sign_extend(val) as i128)
223 size.sign_extend(val) as i128
225 (t.name_str(), actually.to_string())
227 attr::IntType::UnsignedInt(t) => {
228 let actually = size.truncate(val);
229 (t.name_str(), actually.to_string())
232 let mut err = lint.build(&format!("literal out of range for `{}`", t));
234 // If the value is negative,
235 // emits a note about the value itself, apart from the literal.
237 "the literal `{}` (decimal `{}`) does not fit into \
241 err.note(&format!("and the value `-{}` will become `{}{}`", repr_str, actually, t));
244 "the literal `{}` (decimal `{}`) does not fit into \
245 the type `{}` and will become `{}{}`",
246 repr_str, val, t, actually, t
249 if let Some(sugg_ty) =
250 get_type_suggestion(&cx.typeck_results().node_type(expr.hir_id), val, negative)
252 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
253 let (sans_suffix, _) = repr_str.split_at(pos);
256 &format!("consider using the type `{}` instead", sugg_ty),
257 format!("{}{}", sans_suffix, sugg_ty),
258 Applicability::MachineApplicable,
261 err.help(&format!("consider using the type `{}` instead", sugg_ty));
268 // This function finds the next fitting type and generates a suggestion string.
269 // It searches for fitting types in the following way (`X < Y`):
270 // - `iX`: if literal fits in `uX` => `uX`, else => `iY`
274 // No suggestion for: `isize`, `usize`.
275 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
278 macro_rules! find_fit {
279 ($ty:expr, $val:expr, $negative:expr,
280 $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
282 let _neg = if negative { 1 } else { 0 };
285 $(if !negative && val <= uint_ty_range($utypes).1 {
286 return Some($utypes.name_str())
288 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
289 return Some($itypes.name_str())
299 ty::Int(i) => find_fit!(i, val, negative,
300 I8 => [U8] => [I16, I32, I64, I128],
301 I16 => [U16] => [I32, I64, I128],
302 I32 => [U32] => [I64, I128],
303 I64 => [U64] => [I128],
304 I128 => [U128] => []),
305 ty::Uint(u) => find_fit!(u, val, negative,
306 U8 => [U8, U16, U32, U64, U128] => [],
307 U16 => [U16, U32, U64, U128] => [],
308 U32 => [U32, U64, U128] => [],
309 U64 => [U64, U128] => [],
310 U128 => [U128] => []),
315 fn lint_int_literal<'tcx>(
316 cx: &LateContext<'tcx>,
317 type_limits: &TypeLimits,
318 e: &'tcx hir::Expr<'tcx>,
323 let int_type = t.normalize(cx.sess().target.pointer_width);
324 let (min, max) = int_ty_range(int_type);
325 let max = max as u128;
326 let negative = type_limits.negated_expr_id == Some(e.hir_id);
328 // Detect literal value out of range [min, max] inclusive
329 // avoiding use of -min to prevent overflow/panic
330 if (negative && v > max + 1) || (!negative && v > max) {
331 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
332 report_bin_hex_error(
335 attr::IntType::SignedInt(ty::ast_int_ty(t)),
343 let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
344 if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
345 if let hir::ExprKind::Struct(..) = par_e.kind {
346 if is_range_literal(par_e)
347 && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
349 // The overflowing literal lint was overridden.
355 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
356 let mut err = lint.build(&format!("literal out of range for `{}`", t.name_str()));
358 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
361 .span_to_snippet(lit.span)
362 .expect("must get snippet from literal"),
367 if let Some(sugg_ty) =
368 get_type_suggestion(&cx.typeck_results().node_type(e.hir_id), v, negative)
370 err.help(&format!("consider using the type `{}` instead", sugg_ty));
377 fn lint_uint_literal<'tcx>(
378 cx: &LateContext<'tcx>,
379 e: &'tcx hir::Expr<'tcx>,
383 let uint_type = t.normalize(cx.sess().target.pointer_width);
384 let (min, max) = uint_ty_range(uint_type);
385 let lit_val: u128 = match lit.node {
386 // _v is u8, within range by definition
387 ast::LitKind::Byte(_v) => return,
388 ast::LitKind::Int(v, _) => v,
391 if lit_val < min || lit_val > max {
392 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
393 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
395 hir::ExprKind::Cast(..) => {
396 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
397 cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
398 lint.build("only `u8` can be cast into `char`")
401 &"use a `char` literal instead",
402 format!("'\\u{{{:X}}}'", lit_val),
403 Applicability::MachineApplicable,
410 hir::ExprKind::Struct(..) if is_range_literal(par_e) => {
411 let t = t.name_str();
412 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
413 // The overflowing literal lint was overridden.
420 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
421 report_bin_hex_error(
424 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
431 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
432 lint.build(&format!("literal out of range for `{}`", t.name_str()))
434 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
437 .span_to_snippet(lit.span)
438 .expect("must get snippet from literal"),
448 fn lint_literal<'tcx>(
449 cx: &LateContext<'tcx>,
450 type_limits: &TypeLimits,
451 e: &'tcx hir::Expr<'tcx>,
454 match *cx.typeck_results().node_type(e.hir_id).kind() {
457 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
458 lint_int_literal(cx, type_limits, e, lit, t, v)
463 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
465 let is_infinite = match lit.node {
466 ast::LitKind::Float(v, _) => match t {
467 ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
468 ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
472 if is_infinite == Ok(true) {
473 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
474 lint.build(&format!("literal out of range for `{}`", t.name_str()))
476 "the literal `{}` does not fit into the type `{}` and will be converted to `{}::INFINITY`",
479 .span_to_snippet(lit.span)
480 .expect("must get snippet from literal"),
492 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
493 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
495 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
496 // propagate negation, if the negation itself isn't negated
497 if self.negated_expr_id != Some(e.hir_id) {
498 self.negated_expr_id = Some(expr.hir_id);
501 hir::ExprKind::Binary(binop, ref l, ref r) => {
502 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
503 cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
504 lint.build("comparison is useless due to type limits").emit()
508 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
512 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
514 hir::BinOpKind::Lt => v > min && v <= max,
515 hir::BinOpKind::Le => v >= min && v < max,
516 hir::BinOpKind::Gt => v >= min && v < max,
517 hir::BinOpKind::Ge => v > min && v <= max,
518 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
523 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
527 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
528 hir::BinOpKind::Le => hir::BinOpKind::Ge,
529 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
530 hir::BinOpKind::Ge => hir::BinOpKind::Le,
537 cx: &LateContext<'_>,
542 let (lit, expr, swap) = match (&l.kind, &r.kind) {
543 (&hir::ExprKind::Lit(_), _) => (l, r, true),
544 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
547 // Normalize the binop so that the literal is always on the RHS in
549 let norm_binop = if swap { rev_binop(binop) } else { binop };
550 match *cx.typeck_results().node_type(expr.hir_id).kind() {
552 let (min, max) = int_ty_range(int_ty);
553 let lit_val: i128 = match lit.kind {
554 hir::ExprKind::Lit(ref li) => match li.node {
557 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
563 is_valid(norm_binop, lit_val, min, max)
565 ty::Uint(uint_ty) => {
566 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
567 let lit_val: u128 = match lit.kind {
568 hir::ExprKind::Lit(ref li) => match li.node {
569 ast::LitKind::Int(v, _) => v,
574 is_valid(norm_binop, lit_val, min, max)
580 fn is_comparison(binop: hir::BinOp) -> bool {
595 /// The `improper_ctypes` lint detects incorrect use of types in foreign
602 /// static STATIC: String;
610 /// The compiler has several checks to verify that types used in `extern`
611 /// blocks are safe and follow certain rules to ensure proper
612 /// compatibility with the foreign interfaces. This lint is issued when it
613 /// detects a probable mistake in a definition. The lint usually should
614 /// provide a description of the issue, along with possibly a hint on how
618 "proper use of libc types in foreign modules"
621 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
624 /// The `improper_ctypes_definitions` lint detects incorrect use of
625 /// [`extern` function] definitions.
627 /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
632 /// # #![allow(unused)]
633 /// pub extern "C" fn str_type(p: &str) { }
640 /// There are many parameter and return types that may be specified in an
641 /// `extern` function that are not compatible with the given ABI. This
642 /// lint is an alert that these types should not be used. The lint usually
643 /// should provide a description of the issue, along with possibly a hint
644 /// on how to resolve it.
645 IMPROPER_CTYPES_DEFINITIONS,
647 "proper use of libc types in foreign item definitions"
650 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
652 #[derive(Clone, Copy)]
653 crate enum CItemKind {
658 struct ImproperCTypesVisitor<'a, 'tcx> {
659 cx: &'a LateContext<'tcx>,
663 enum FfiResult<'tcx> {
665 FfiPhantom(Ty<'tcx>),
666 FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option<String> },
669 crate fn nonnull_optimization_guaranteed<'tcx>(tcx: TyCtxt<'tcx>, def: &ty::AdtDef) -> bool {
670 tcx.get_attrs(def.did)
672 .any(|a| tcx.sess.check_name(a, sym::rustc_nonnull_optimization_guaranteed))
675 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
677 pub fn transparent_newtype_field<'a, 'tcx>(
679 variant: &'a ty::VariantDef,
680 ) -> Option<&'a ty::FieldDef> {
681 let param_env = tcx.param_env(variant.def_id);
682 for field in &variant.fields {
683 let field_ty = tcx.type_of(field.did);
684 let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
694 /// Is type known to be non-null?
695 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
698 ty::FnPtr(_) => true,
700 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
701 ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
702 let marked_non_null = nonnull_optimization_guaranteed(tcx, &def);
708 // Types with a `#[repr(no_niche)]` attribute have their niche hidden.
709 // The attribute is used by the UnsafeCell for example (the only use so far).
710 if def.repr.hide_niche() {
714 for variant in &def.variants {
715 if let Some(field) = transparent_newtype_field(cx.tcx, variant) {
716 if ty_is_known_nonnull(cx, field.ty(tcx, substs), mode) {
728 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
729 /// If the type passed in was not scalar, returns None.
730 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
732 Some(match *ty.kind() {
733 ty::Adt(field_def, field_substs) => {
734 let inner_field_ty = {
735 let first_non_zst_ty =
736 field_def.variants.iter().filter_map(|v| transparent_newtype_field(cx.tcx, v));
738 first_non_zst_ty.clone().count(),
740 "Wrong number of fields for transparent type"
744 .expect("No non-zst fields in transparent type.")
745 .ty(tcx, field_substs)
747 return get_nullable_type(cx, inner_field_ty);
749 ty::Int(ty) => tcx.mk_mach_int(ty),
750 ty::Uint(ty) => tcx.mk_mach_uint(ty),
751 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
752 // As these types are always non-null, the nullable equivalent of
753 // Option<T> of these types are their raw pointer counterparts.
754 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
756 // There is no nullable equivalent for Rust's function pointers -- you
757 // must use an Option<fn(..) -> _> to represent it.
761 // We should only ever reach this case if ty_is_known_nonnull is extended
765 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
773 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
774 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
775 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
776 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
777 /// FIXME: This duplicates code in codegen.
778 crate fn repr_nullable_ptr<'tcx>(
779 cx: &LateContext<'tcx>,
782 ) -> Option<Ty<'tcx>> {
783 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
784 if let ty::Adt(ty_def, substs) = ty.kind() {
785 if ty_def.variants.len() != 2 {
789 let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
790 let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
791 let fields = if variant_fields[0].is_empty() {
793 } else if variant_fields[1].is_empty() {
799 if fields.len() != 1 {
803 let field_ty = fields[0].ty(cx.tcx, substs);
804 if !ty_is_known_nonnull(cx, field_ty, ckind) {
808 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
809 // If the computed size for the field and the enum are different, the nonnull optimization isn't
810 // being applied (and we've got a problem somewhere).
811 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
812 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
813 bug!("improper_ctypes: Option nonnull optimization not applied?");
816 // Return the nullable type this Option-like enum can be safely represented with.
817 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
818 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
819 match (field_ty_scalar.valid_range.start(), field_ty_scalar.valid_range.end()) {
820 (0, _) => unreachable!("Non-null optimisation extended to a non-zero value."),
822 return Some(get_nullable_type(cx, field_ty).unwrap());
824 (start, end) => unreachable!("Unhandled start and end range: ({}, {})", start, end),
831 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
832 /// Check if the type is array and emit an unsafe type lint.
833 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
834 if let ty::Array(..) = ty.kind() {
835 self.emit_ffi_unsafe_type_lint(
838 "passing raw arrays by value is not FFI-safe",
839 Some("consider passing a pointer to the array"),
847 /// Checks if the given field's type is "ffi-safe".
848 fn check_field_type_for_ffi(
850 cache: &mut FxHashSet<Ty<'tcx>>,
851 field: &ty::FieldDef,
852 substs: SubstsRef<'tcx>,
853 ) -> FfiResult<'tcx> {
854 let field_ty = field.ty(self.cx.tcx, substs);
855 if field_ty.has_opaque_types() {
856 self.check_type_for_ffi(cache, field_ty)
858 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
859 self.check_type_for_ffi(cache, field_ty)
863 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
864 fn check_variant_for_ffi(
866 cache: &mut FxHashSet<Ty<'tcx>>,
869 variant: &ty::VariantDef,
870 substs: SubstsRef<'tcx>,
871 ) -> FfiResult<'tcx> {
874 if def.repr.transparent() {
875 // Can assume that only one field is not a ZST, so only check
876 // that field's type for FFI-safety.
877 if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
878 self.check_field_type_for_ffi(cache, field, substs)
880 bug!("malformed transparent type");
883 // We can't completely trust repr(C) markings; make sure the fields are
885 let mut all_phantom = !variant.fields.is_empty();
886 for field in &variant.fields {
887 match self.check_field_type_for_ffi(cache, &field, substs) {
891 FfiPhantom(..) if def.is_enum() => {
894 reason: "this enum contains a PhantomData field".into(),
903 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
907 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
908 /// representation which can be exported to C code).
909 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
912 let tcx = self.cx.tcx;
914 // Protect against infinite recursion, for example
915 // `struct S(*mut S);`.
916 // FIXME: A recursion limit is necessary as well, for irregular
918 if !cache.insert(ty) {
923 ty::Adt(def, _) if def.is_box() && matches!(self.mode, CItemKind::Definition) => {
927 ty::Adt(def, substs) => {
928 if def.is_phantom_data() {
929 return FfiPhantom(ty);
931 match def.adt_kind() {
932 AdtKind::Struct | AdtKind::Union => {
933 let kind = if def.is_struct() { "struct" } else { "union" };
935 if !def.repr.c() && !def.repr.transparent() {
938 reason: format!("this {} has unspecified layout", kind),
940 "consider adding a `#[repr(C)]` or \
941 `#[repr(transparent)]` attribute to this {}",
947 let is_non_exhaustive =
948 def.non_enum_variant().is_field_list_non_exhaustive();
949 if is_non_exhaustive && !def.did.is_local() {
952 reason: format!("this {} is non-exhaustive", kind),
957 if def.non_enum_variant().fields.is_empty() {
960 reason: format!("this {} has no fields", kind),
961 help: Some(format!("consider adding a member to this {}", kind)),
965 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
968 if def.variants.is_empty() {
969 // Empty enums are okay... although sort of useless.
973 // Check for a repr() attribute to specify the size of the
975 if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
976 // Special-case types like `Option<extern fn()>`.
977 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
980 reason: "enum has no representation hint".into(),
982 "consider adding a `#[repr(C)]`, \
983 `#[repr(transparent)]`, or integer `#[repr(...)]` \
984 attribute to this enum"
991 if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
994 reason: "this enum is non-exhaustive".into(),
999 // Check the contained variants.
1000 for variant in &def.variants {
1001 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1002 if is_non_exhaustive && !variant.def_id.is_local() {
1005 reason: "this enum has non-exhaustive variants".into(),
1010 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1021 ty::Char => FfiUnsafe {
1023 reason: "the `char` type has no C equivalent".into(),
1024 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
1027 ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => FfiUnsafe {
1029 reason: "128-bit integers don't currently have a known stable ABI".into(),
1033 // Primitive types with a stable representation.
1034 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1036 ty::Slice(_) => FfiUnsafe {
1038 reason: "slices have no C equivalent".into(),
1039 help: Some("consider using a raw pointer instead".into()),
1042 ty::Dynamic(..) => {
1043 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
1046 ty::Str => FfiUnsafe {
1048 reason: "string slices have no C equivalent".into(),
1049 help: Some("consider using `*const u8` and a length instead".into()),
1052 ty::Tuple(..) => FfiUnsafe {
1054 reason: "tuples have unspecified layout".into(),
1055 help: Some("consider using a struct instead".into()),
1058 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1060 matches!(self.mode, CItemKind::Definition)
1061 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1067 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1068 self.check_type_for_ffi(cache, ty)
1071 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1074 if self.is_internal_abi(sig.abi()) {
1077 reason: "this function pointer has Rust-specific calling convention".into(),
1079 "consider using an `extern fn(...) -> ...` \
1080 function pointer instead"
1086 let sig = tcx.erase_late_bound_regions(sig);
1087 if !sig.output().is_unit() {
1088 let r = self.check_type_for_ffi(cache, sig.output());
1096 for arg in sig.inputs() {
1097 let r = self.check_type_for_ffi(cache, arg);
1108 ty::Foreign(..) => FfiSafe,
1110 // While opaque types are checked for earlier, if a projection in a struct field
1111 // normalizes to an opaque type, then it will reach this branch.
1113 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
1116 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1117 // so they are currently ignored for the purposes of this lint.
1118 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1123 | ty::Projection(..)
1129 | ty::GeneratorWitness(..)
1130 | ty::Placeholder(..)
1131 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1135 fn emit_ffi_unsafe_type_lint(
1142 let lint = match self.mode {
1143 CItemKind::Declaration => IMPROPER_CTYPES,
1144 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1147 self.cx.struct_span_lint(lint, sp, |lint| {
1148 let item_description = match self.mode {
1149 CItemKind::Declaration => "block",
1150 CItemKind::Definition => "fn",
1152 let mut diag = lint.build(&format!(
1153 "`extern` {} uses type `{}`, which is not FFI-safe",
1154 item_description, ty
1156 diag.span_label(sp, "not FFI-safe");
1157 if let Some(help) = help {
1161 if let ty::Adt(def, _) = ty.kind() {
1162 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
1163 diag.span_note(sp, "the type is defined here");
1170 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1171 struct ProhibitOpaqueTypes<'a, 'tcx> {
1172 cx: &'a LateContext<'tcx>,
1175 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1176 type BreakTy = Ty<'tcx>;
1178 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1180 ty::Opaque(..) => ControlFlow::Break(ty),
1181 // Consider opaque types within projections FFI-safe if they do not normalize
1182 // to more opaque types.
1183 ty::Projection(..) => {
1184 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1186 // If `ty` is a opaque type directly then `super_visit_with` won't invoke
1187 // this function again.
1188 if ty.has_opaque_types() {
1191 ControlFlow::CONTINUE
1194 _ => ty.super_visit_with(self),
1199 if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1200 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
1207 fn check_type_for_ffi_and_report_errors(
1212 is_return_type: bool,
1214 // We have to check for opaque types before `normalize_erasing_regions`,
1215 // which will replace opaque types with their underlying concrete type.
1216 if self.check_for_opaque_ty(sp, ty) {
1217 // We've already emitted an error due to an opaque type.
1221 // it is only OK to use this function because extern fns cannot have
1222 // any generic types right now:
1223 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1225 // C doesn't really support passing arrays by value - the only way to pass an array by value
1226 // is through a struct. So, first test that the top level isn't an array, and then
1227 // recursively check the types inside.
1228 if !is_static && self.check_for_array_ty(sp, ty) {
1232 // Don't report FFI errors for unit return types. This check exists here, and not in
1233 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1235 if is_return_type && ty.is_unit() {
1239 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1240 FfiResult::FfiSafe => {}
1241 FfiResult::FfiPhantom(ty) => {
1242 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1244 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1245 // argument, which after substitution, is `()`, then this branch can be hit.
1246 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1247 FfiResult::FfiUnsafe { ty, reason, help } => {
1248 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1253 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1254 let def_id = self.cx.tcx.hir().local_def_id(id);
1255 let sig = self.cx.tcx.fn_sig(def_id);
1256 let sig = self.cx.tcx.erase_late_bound_regions(sig);
1258 for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
1259 self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false);
1262 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1263 let ret_ty = sig.output();
1264 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1268 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1269 let def_id = self.cx.tcx.hir().local_def_id(id);
1270 let ty = self.cx.tcx.type_of(def_id);
1271 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1274 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1277 SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1282 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1283 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1284 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1285 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1287 if !vis.is_internal_abi(abi) {
1289 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1290 vis.check_foreign_fn(it.hir_id(), decl);
1292 hir::ForeignItemKind::Static(ref ty, _) => {
1293 vis.check_foreign_static(it.hir_id(), ty.span);
1295 hir::ForeignItemKind::Type => (),
1301 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1304 cx: &LateContext<'tcx>,
1305 kind: hir::intravisit::FnKind<'tcx>,
1306 decl: &'tcx hir::FnDecl<'_>,
1307 _: &'tcx hir::Body<'_>,
1311 use hir::intravisit::FnKind;
1313 let abi = match kind {
1314 FnKind::ItemFn(_, _, header, ..) => header.abi,
1315 FnKind::Method(_, sig, ..) => sig.header.abi,
1319 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1320 if !vis.is_internal_abi(abi) {
1321 vis.check_foreign_fn(hir_id, decl);
1326 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1328 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1329 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1330 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1331 let t = cx.tcx.type_of(it.def_id);
1332 let ty = cx.tcx.erase_regions(t);
1333 let layout = match cx.layout_of(ty) {
1334 Ok(layout) => layout,
1336 ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
1339 let (variants, tag) = match layout.variants {
1340 Variants::Multiple {
1341 tag_encoding: TagEncoding::Direct,
1345 } => (variants, tag),
1349 let tag_size = tag.value.size(&cx.tcx).bytes();
1352 "enum `{}` is {} bytes large with layout:\n{:#?}",
1354 layout.size.bytes(),
1358 let (largest, slargest, largest_index) = enum_definition
1362 .map(|(variant, variant_layout)| {
1363 // Subtract the size of the enum tag.
1364 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1366 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1370 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1373 } else if size > s {
1380 // We only warn if the largest variant is at least thrice as large as
1381 // the second-largest.
1382 if largest > slargest * 3 && slargest > 0 {
1383 cx.struct_span_lint(
1384 VARIANT_SIZE_DIFFERENCES,
1385 enum_definition.variants[largest_index].span,
1387 lint.build(&format!(
1388 "enum variant is more than three times \
1389 larger ({} bytes) than the next largest",