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 `{}` instead", sugg_ty),
242 format!("{}{}", sans_suffix, sugg_ty),
243 Applicability::MachineApplicable,
246 err.help(&format!("consider using `{}` 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 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"),
357 fn lint_uint_literal<'tcx>(
358 cx: &LateContext<'tcx>,
359 e: &'tcx hir::Expr<'tcx>,
363 let uint_type = t.normalize(cx.sess().target.pointer_width);
364 let (min, max) = uint_ty_range(uint_type);
365 let lit_val: u128 = match lit.node {
366 // _v is u8, within range by definition
367 ast::LitKind::Byte(_v) => return,
368 ast::LitKind::Int(v, _) => v,
371 if lit_val < min || lit_val > max {
372 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
373 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
375 hir::ExprKind::Cast(..) => {
376 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
377 cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
378 lint.build("only `u8` can be cast into `char`")
381 &"use a `char` literal instead",
382 format!("'\\u{{{:X}}}'", lit_val),
383 Applicability::MachineApplicable,
390 hir::ExprKind::Struct(..) if is_range_literal(par_e) => {
391 let t = t.name_str();
392 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
393 // The overflowing literal lint was overridden.
400 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
401 report_bin_hex_error(
404 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
411 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
412 lint.build(&format!("literal out of range for `{}`", t.name_str()))
414 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
417 .span_to_snippet(lit.span)
418 .expect("must get snippet from literal"),
428 fn lint_literal<'tcx>(
429 cx: &LateContext<'tcx>,
430 type_limits: &TypeLimits,
431 e: &'tcx hir::Expr<'tcx>,
434 match *cx.typeck_results().node_type(e.hir_id).kind() {
437 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
438 lint_int_literal(cx, type_limits, e, lit, t, v)
443 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
445 let is_infinite = match lit.node {
446 ast::LitKind::Float(v, _) => match t {
447 ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
448 ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
452 if is_infinite == Ok(true) {
453 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
454 lint.build(&format!("literal out of range for `{}`", t.name_str()))
456 "the literal `{}` does not fit into the type `{}` and will be converted to `{}::INFINITY`",
459 .span_to_snippet(lit.span)
460 .expect("must get snippet from literal"),
472 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
473 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
475 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
476 // propagate negation, if the negation itself isn't negated
477 if self.negated_expr_id != Some(e.hir_id) {
478 self.negated_expr_id = Some(expr.hir_id);
481 hir::ExprKind::Binary(binop, ref l, ref r) => {
482 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
483 cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
484 lint.build("comparison is useless due to type limits").emit()
488 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
492 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
494 hir::BinOpKind::Lt => v > min && v <= max,
495 hir::BinOpKind::Le => v >= min && v < max,
496 hir::BinOpKind::Gt => v >= min && v < max,
497 hir::BinOpKind::Ge => v > min && v <= max,
498 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
503 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
507 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
508 hir::BinOpKind::Le => hir::BinOpKind::Ge,
509 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
510 hir::BinOpKind::Ge => hir::BinOpKind::Le,
517 cx: &LateContext<'_>,
522 let (lit, expr, swap) = match (&l.kind, &r.kind) {
523 (&hir::ExprKind::Lit(_), _) => (l, r, true),
524 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
527 // Normalize the binop so that the literal is always on the RHS in
529 let norm_binop = if swap { rev_binop(binop) } else { binop };
530 match *cx.typeck_results().node_type(expr.hir_id).kind() {
532 let (min, max) = int_ty_range(int_ty);
533 let lit_val: i128 = match lit.kind {
534 hir::ExprKind::Lit(ref li) => match li.node {
537 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
543 is_valid(norm_binop, lit_val, min, max)
545 ty::Uint(uint_ty) => {
546 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
547 let lit_val: u128 = match lit.kind {
548 hir::ExprKind::Lit(ref li) => match li.node {
549 ast::LitKind::Int(v, _) => v,
554 is_valid(norm_binop, lit_val, min, max)
560 fn is_comparison(binop: hir::BinOp) -> bool {
575 /// The `improper_ctypes` lint detects incorrect use of types in foreign
582 /// static STATIC: String;
590 /// The compiler has several checks to verify that types used in `extern`
591 /// blocks are safe and follow certain rules to ensure proper
592 /// compatibility with the foreign interfaces. This lint is issued when it
593 /// detects a probable mistake in a definition. The lint usually should
594 /// provide a description of the issue, along with possibly a hint on how
598 "proper use of libc types in foreign modules"
601 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
604 /// The `improper_ctypes_definitions` lint detects incorrect use of
605 /// [`extern` function] definitions.
607 /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
612 /// # #![allow(unused)]
613 /// pub extern "C" fn str_type(p: &str) { }
620 /// There are many parameter and return types that may be specified in an
621 /// `extern` function that are not compatible with the given ABI. This
622 /// lint is an alert that these types should not be used. The lint usually
623 /// should provide a description of the issue, along with possibly a hint
624 /// on how to resolve it.
625 IMPROPER_CTYPES_DEFINITIONS,
627 "proper use of libc types in foreign item definitions"
630 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
632 #[derive(Clone, Copy)]
633 crate enum CItemKind {
638 struct ImproperCTypesVisitor<'a, 'tcx> {
639 cx: &'a LateContext<'tcx>,
643 enum FfiResult<'tcx> {
645 FfiPhantom(Ty<'tcx>),
646 FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option<String> },
649 crate fn nonnull_optimization_guaranteed<'tcx>(tcx: TyCtxt<'tcx>, def: &ty::AdtDef) -> bool {
650 tcx.get_attrs(def.did)
652 .any(|a| tcx.sess.check_name(a, sym::rustc_nonnull_optimization_guaranteed))
655 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
657 pub fn transparent_newtype_field<'a, 'tcx>(
659 variant: &'a ty::VariantDef,
660 ) -> Option<&'a ty::FieldDef> {
661 let param_env = tcx.param_env(variant.def_id);
662 for field in &variant.fields {
663 let field_ty = tcx.type_of(field.did);
664 let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
674 /// Is type known to be non-null?
675 crate fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
678 ty::FnPtr(_) => true,
680 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
681 ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
682 let marked_non_null = nonnull_optimization_guaranteed(tcx, &def);
688 for variant in &def.variants {
689 if let Some(field) = transparent_newtype_field(cx.tcx, variant) {
690 if ty_is_known_nonnull(cx, field.ty(tcx, substs), mode) {
702 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
703 /// If the type passed in was not scalar, returns None.
704 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
706 Some(match *ty.kind() {
707 ty::Adt(field_def, field_substs) => {
708 let inner_field_ty = {
709 let first_non_zst_ty =
710 field_def.variants.iter().filter_map(|v| transparent_newtype_field(cx.tcx, v));
712 first_non_zst_ty.clone().count(),
714 "Wrong number of fields for transparent type"
718 .expect("No non-zst fields in transparent type.")
719 .ty(tcx, field_substs)
721 return get_nullable_type(cx, inner_field_ty);
723 ty::Int(ty) => tcx.mk_mach_int(ty),
724 ty::Uint(ty) => tcx.mk_mach_uint(ty),
725 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
726 // As these types are always non-null, the nullable equivalent of
727 // Option<T> of these types are their raw pointer counterparts.
728 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
730 // There is no nullable equivalent for Rust's function pointers -- you
731 // must use an Option<fn(..) -> _> to represent it.
735 // We should only ever reach this case if ty_is_known_nonnull is extended
739 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
747 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
748 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
749 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
750 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
751 /// FIXME: This duplicates code in codegen.
752 crate fn repr_nullable_ptr<'tcx>(
753 cx: &LateContext<'tcx>,
756 ) -> Option<Ty<'tcx>> {
757 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
758 if let ty::Adt(ty_def, substs) = ty.kind() {
759 if ty_def.variants.len() != 2 {
763 let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
764 let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
765 let fields = if variant_fields[0].is_empty() {
767 } else if variant_fields[1].is_empty() {
773 if fields.len() != 1 {
777 let field_ty = fields[0].ty(cx.tcx, substs);
778 if !ty_is_known_nonnull(cx, field_ty, ckind) {
782 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
783 // If the computed size for the field and the enum are different, the nonnull optimization isn't
784 // being applied (and we've got a problem somewhere).
785 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
786 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
787 bug!("improper_ctypes: Option nonnull optimization not applied?");
790 // Return the nullable type this Option-like enum can be safely represented with.
791 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
792 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
793 match (field_ty_scalar.valid_range.start(), field_ty_scalar.valid_range.end()) {
794 (0, _) => unreachable!("Non-null optimisation extended to a non-zero value."),
796 return Some(get_nullable_type(cx, field_ty).unwrap());
798 (start, end) => unreachable!("Unhandled start and end range: ({}, {})", start, end),
805 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
806 /// Check if the type is array and emit an unsafe type lint.
807 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
808 if let ty::Array(..) = ty.kind() {
809 self.emit_ffi_unsafe_type_lint(
812 "passing raw arrays by value is not FFI-safe",
813 Some("consider passing a pointer to the array"),
821 /// Checks if the given field's type is "ffi-safe".
822 fn check_field_type_for_ffi(
824 cache: &mut FxHashSet<Ty<'tcx>>,
825 field: &ty::FieldDef,
826 substs: SubstsRef<'tcx>,
827 ) -> FfiResult<'tcx> {
828 let field_ty = field.ty(self.cx.tcx, substs);
829 if field_ty.has_opaque_types() {
830 self.check_type_for_ffi(cache, field_ty)
832 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
833 self.check_type_for_ffi(cache, field_ty)
837 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
838 fn check_variant_for_ffi(
840 cache: &mut FxHashSet<Ty<'tcx>>,
843 variant: &ty::VariantDef,
844 substs: SubstsRef<'tcx>,
845 ) -> FfiResult<'tcx> {
848 if def.repr.transparent() {
849 // Can assume that only one field is not a ZST, so only check
850 // that field's type for FFI-safety.
851 if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
852 self.check_field_type_for_ffi(cache, field, substs)
854 bug!("malformed transparent type");
857 // We can't completely trust repr(C) markings; make sure the fields are
859 let mut all_phantom = !variant.fields.is_empty();
860 for field in &variant.fields {
861 match self.check_field_type_for_ffi(cache, &field, substs) {
865 FfiPhantom(..) if def.is_enum() => {
868 reason: "this enum contains a PhantomData field".into(),
877 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
881 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
882 /// representation which can be exported to C code).
883 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
886 let tcx = self.cx.tcx;
888 // Protect against infinite recursion, for example
889 // `struct S(*mut S);`.
890 // FIXME: A recursion limit is necessary as well, for irregular
892 if !cache.insert(ty) {
897 ty::Adt(def, _) if def.is_box() && matches!(self.mode, CItemKind::Definition) => {
901 ty::Adt(def, substs) => {
902 if def.is_phantom_data() {
903 return FfiPhantom(ty);
905 match def.adt_kind() {
906 AdtKind::Struct | AdtKind::Union => {
907 let kind = if def.is_struct() { "struct" } else { "union" };
909 if !def.repr.c() && !def.repr.transparent() {
912 reason: format!("this {} has unspecified layout", kind),
914 "consider adding a `#[repr(C)]` or \
915 `#[repr(transparent)]` attribute to this {}",
921 let is_non_exhaustive =
922 def.non_enum_variant().is_field_list_non_exhaustive();
923 if is_non_exhaustive && !def.did.is_local() {
926 reason: format!("this {} is non-exhaustive", kind),
931 if def.non_enum_variant().fields.is_empty() {
934 reason: format!("this {} has no fields", kind),
935 help: Some(format!("consider adding a member to this {}", kind)),
939 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
942 if def.variants.is_empty() {
943 // Empty enums are okay... although sort of useless.
947 // Check for a repr() attribute to specify the size of the
949 if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
950 // Special-case types like `Option<extern fn()>`.
951 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
954 reason: "enum has no representation hint".into(),
956 "consider adding a `#[repr(C)]`, \
957 `#[repr(transparent)]`, or integer `#[repr(...)]` \
958 attribute to this enum"
965 if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
968 reason: "this enum is non-exhaustive".into(),
973 // Check the contained variants.
974 for variant in &def.variants {
975 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
976 if is_non_exhaustive && !variant.def_id.is_local() {
979 reason: "this enum has non-exhaustive variants".into(),
984 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
995 ty::Char => FfiUnsafe {
997 reason: "the `char` type has no C equivalent".into(),
998 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
1001 ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => FfiUnsafe {
1003 reason: "128-bit integers don't currently have a known stable ABI".into(),
1007 // Primitive types with a stable representation.
1008 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1010 ty::Slice(_) => FfiUnsafe {
1012 reason: "slices have no C equivalent".into(),
1013 help: Some("consider using a raw pointer instead".into()),
1016 ty::Dynamic(..) => {
1017 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
1020 ty::Str => FfiUnsafe {
1022 reason: "string slices have no C equivalent".into(),
1023 help: Some("consider using `*const u8` and a length instead".into()),
1026 ty::Tuple(..) => FfiUnsafe {
1028 reason: "tuples have unspecified layout".into(),
1029 help: Some("consider using a struct instead".into()),
1032 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1034 matches!(self.mode, CItemKind::Definition)
1035 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1041 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1042 self.check_type_for_ffi(cache, ty)
1045 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1048 if self.is_internal_abi(sig.abi()) {
1051 reason: "this function pointer has Rust-specific calling convention".into(),
1053 "consider using an `extern fn(...) -> ...` \
1054 function pointer instead"
1060 let sig = tcx.erase_late_bound_regions(sig);
1061 if !sig.output().is_unit() {
1062 let r = self.check_type_for_ffi(cache, sig.output());
1070 for arg in sig.inputs() {
1071 let r = self.check_type_for_ffi(cache, arg);
1082 ty::Foreign(..) => FfiSafe,
1084 // While opaque types are checked for earlier, if a projection in a struct field
1085 // normalizes to an opaque type, then it will reach this branch.
1087 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
1090 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1091 // so they are currently ignored for the purposes of this lint.
1092 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1097 | ty::Projection(..)
1103 | ty::GeneratorWitness(..)
1104 | ty::Placeholder(..)
1105 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1109 fn emit_ffi_unsafe_type_lint(
1116 let lint = match self.mode {
1117 CItemKind::Declaration => IMPROPER_CTYPES,
1118 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1121 self.cx.struct_span_lint(lint, sp, |lint| {
1122 let item_description = match self.mode {
1123 CItemKind::Declaration => "block",
1124 CItemKind::Definition => "fn",
1126 let mut diag = lint.build(&format!(
1127 "`extern` {} uses type `{}`, which is not FFI-safe",
1128 item_description, ty
1130 diag.span_label(sp, "not FFI-safe");
1131 if let Some(help) = help {
1135 if let ty::Adt(def, _) = ty.kind() {
1136 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
1137 diag.span_note(sp, "the type is defined here");
1144 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1145 struct ProhibitOpaqueTypes<'a, 'tcx> {
1146 cx: &'a LateContext<'tcx>,
1149 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1150 type BreakTy = Ty<'tcx>;
1152 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1154 ty::Opaque(..) => ControlFlow::Break(ty),
1155 // Consider opaque types within projections FFI-safe if they do not normalize
1156 // to more opaque types.
1157 ty::Projection(..) => {
1158 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1160 // If `ty` is a opaque type directly then `super_visit_with` won't invoke
1161 // this function again.
1162 if ty.has_opaque_types() {
1165 ControlFlow::CONTINUE
1168 _ => ty.super_visit_with(self),
1173 if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1174 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
1181 fn check_type_for_ffi_and_report_errors(
1186 is_return_type: bool,
1188 // We have to check for opaque types before `normalize_erasing_regions`,
1189 // which will replace opaque types with their underlying concrete type.
1190 if self.check_for_opaque_ty(sp, ty) {
1191 // We've already emitted an error due to an opaque type.
1195 // it is only OK to use this function because extern fns cannot have
1196 // any generic types right now:
1197 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1199 // C doesn't really support passing arrays by value - the only way to pass an array by value
1200 // is through a struct. So, first test that the top level isn't an array, and then
1201 // recursively check the types inside.
1202 if !is_static && self.check_for_array_ty(sp, ty) {
1206 // Don't report FFI errors for unit return types. This check exists here, and not in
1207 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1209 if is_return_type && ty.is_unit() {
1213 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1214 FfiResult::FfiSafe => {}
1215 FfiResult::FfiPhantom(ty) => {
1216 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1218 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1219 // argument, which after substitution, is `()`, then this branch can be hit.
1220 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1221 FfiResult::FfiUnsafe { ty, reason, help } => {
1222 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1227 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1228 let def_id = self.cx.tcx.hir().local_def_id(id);
1229 let sig = self.cx.tcx.fn_sig(def_id);
1230 let sig = self.cx.tcx.erase_late_bound_regions(sig);
1232 for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
1233 self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false);
1236 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1237 let ret_ty = sig.output();
1238 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1242 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1243 let def_id = self.cx.tcx.hir().local_def_id(id);
1244 let ty = self.cx.tcx.type_of(def_id);
1245 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1248 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1251 SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1256 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1257 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1258 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1259 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
1261 if !vis.is_internal_abi(abi) {
1263 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1264 vis.check_foreign_fn(it.hir_id, decl);
1266 hir::ForeignItemKind::Static(ref ty, _) => {
1267 vis.check_foreign_static(it.hir_id, ty.span);
1269 hir::ForeignItemKind::Type => (),
1275 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1278 cx: &LateContext<'tcx>,
1279 kind: hir::intravisit::FnKind<'tcx>,
1280 decl: &'tcx hir::FnDecl<'_>,
1281 _: &'tcx hir::Body<'_>,
1285 use hir::intravisit::FnKind;
1287 let abi = match kind {
1288 FnKind::ItemFn(_, _, header, ..) => header.abi,
1289 FnKind::Method(_, sig, ..) => sig.header.abi,
1293 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1294 if !vis.is_internal_abi(abi) {
1295 vis.check_foreign_fn(hir_id, decl);
1300 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1302 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1303 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1304 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1305 let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1306 let t = cx.tcx.type_of(item_def_id);
1307 let ty = cx.tcx.erase_regions(t);
1308 let layout = match cx.layout_of(ty) {
1309 Ok(layout) => layout,
1311 ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
1314 let (variants, tag) = match layout.variants {
1315 Variants::Multiple {
1316 tag_encoding: TagEncoding::Direct,
1320 } => (variants, tag),
1324 let tag_size = tag.value.size(&cx.tcx).bytes();
1327 "enum `{}` is {} bytes large with layout:\n{:#?}",
1329 layout.size.bytes(),
1333 let (largest, slargest, largest_index) = enum_definition
1337 .map(|(variant, variant_layout)| {
1338 // Subtract the size of the enum tag.
1339 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1341 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1345 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1348 } else if size > s {
1355 // We only warn if the largest variant is at least thrice as large as
1356 // the second-largest.
1357 if largest > slargest * 3 && slargest > 0 {
1358 cx.struct_span_lint(
1359 VARIANT_SIZE_DIFFERENCES,
1360 enum_definition.variants[largest_index].span,
1362 lint.build(&format!(
1363 "enum variant is more than three times \
1364 larger ({} bytes) than the next largest",