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, 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::{Integer, LayoutOf, TagEncoding, VariantIdx, Variants};
19 use rustc_target::spec::abi::Abi;
27 "comparisons made useless by limits of the types involved"
33 "literal out of range for its type"
37 VARIANT_SIZE_DIFFERENCES,
39 "detects enums with widely varying variant sizes"
42 #[derive(Copy, Clone)]
43 pub struct TypeLimits {
44 /// Id of the last visited negated expression
45 negated_expr_id: Option<hir::HirId>,
48 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
51 pub fn new() -> TypeLimits {
52 TypeLimits { negated_expr_id: None }
56 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
57 /// Returns `true` iff the lint was overridden.
58 fn lint_overflowing_range_endpoint<'tcx>(
59 cx: &LateContext<'tcx>,
63 expr: &'tcx hir::Expr<'tcx>,
64 parent_expr: &'tcx hir::Expr<'tcx>,
67 // We only want to handle exclusive (`..`) ranges,
68 // which are represented as `ExprKind::Struct`.
69 let mut overwritten = false;
70 if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
74 // We can suggest using an inclusive range
75 // (`..=`) instead only if it is the `end` that is
76 // overflowing and only by 1.
77 if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
78 cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| {
79 let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty));
80 if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
81 use ast::{LitIntType, LitKind};
82 // We need to preserve the literal's suffix,
83 // as it may determine typing information.
84 let suffix = match lit.node {
85 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str().to_string(),
86 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str().to_string(),
87 LitKind::Int(_, LitIntType::Unsuffixed) => "".to_string(),
90 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
93 &"use an inclusive range instead",
95 Applicability::MachineApplicable,
106 // For `isize` & `usize`, be conservative with the warnings, so that the
107 // warnings are consistent between 32- and 64-bit platforms.
108 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
110 ast::IntTy::Isize => (i64::MIN as i128, i64::MAX as i128),
111 ast::IntTy::I8 => (i8::MIN as i64 as i128, i8::MAX as i128),
112 ast::IntTy::I16 => (i16::MIN as i64 as i128, i16::MAX as i128),
113 ast::IntTy::I32 => (i32::MIN as i64 as i128, i32::MAX as i128),
114 ast::IntTy::I64 => (i64::MIN as i128, i64::MAX as i128),
115 ast::IntTy::I128 => (i128::MIN as i128, i128::MAX),
119 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
121 ast::UintTy::Usize => (u64::MIN as u128, u64::MAX as u128),
122 ast::UintTy::U8 => (u8::MIN as u128, u8::MAX as u128),
123 ast::UintTy::U16 => (u16::MIN as u128, u16::MAX as u128),
124 ast::UintTy::U32 => (u32::MIN as u128, u32::MAX as u128),
125 ast::UintTy::U64 => (u64::MIN as u128, u64::MAX as u128),
126 ast::UintTy::U128 => (u128::MIN, u128::MAX),
130 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
131 let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
132 let firstch = src.chars().next()?;
135 match src.chars().nth(1) {
136 Some('x' | 'b') => return Some(src),
144 fn report_bin_hex_error(
145 cx: &LateContext<'_>,
146 expr: &hir::Expr<'_>,
152 let size = Integer::from_attr(&cx.tcx, ty).size();
153 cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
154 let (t, actually) = match ty {
155 attr::IntType::SignedInt(t) => {
156 let actually = sign_extend(val, size) as i128;
157 (t.name_str(), actually.to_string())
159 attr::IntType::UnsignedInt(t) => {
160 let actually = truncate(val, size);
161 (t.name_str(), actually.to_string())
164 let mut err = lint.build(&format!("literal out of range for {}", t));
166 "the literal `{}` (decimal `{}`) does not fit into \
167 the type `{}` and will become `{}{}`",
168 repr_str, val, t, actually, t
170 if let Some(sugg_ty) =
171 get_type_suggestion(&cx.typeck_results().node_type(expr.hir_id), val, negative)
173 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
174 let (sans_suffix, _) = repr_str.split_at(pos);
177 &format!("consider using `{}` instead", sugg_ty),
178 format!("{}{}", sans_suffix, sugg_ty),
179 Applicability::MachineApplicable,
182 err.help(&format!("consider using `{}` instead", sugg_ty));
189 // This function finds the next fitting type and generates a suggestion string.
190 // It searches for fitting types in the following way (`X < Y`):
191 // - `iX`: if literal fits in `uX` => `uX`, else => `iY`
195 // No suggestion for: `isize`, `usize`.
196 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
197 use rustc_ast::ast::IntTy::*;
198 use rustc_ast::ast::UintTy::*;
199 macro_rules! find_fit {
200 ($ty:expr, $val:expr, $negative:expr,
201 $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
203 let _neg = if negative { 1 } else { 0 };
206 $(if !negative && val <= uint_ty_range($utypes).1 {
207 return Some($utypes.name_str())
209 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
210 return Some($itypes.name_str())
220 ty::Int(i) => find_fit!(i, val, negative,
221 I8 => [U8] => [I16, I32, I64, I128],
222 I16 => [U16] => [I32, I64, I128],
223 I32 => [U32] => [I64, I128],
224 I64 => [U64] => [I128],
225 I128 => [U128] => []),
226 ty::Uint(u) => find_fit!(u, val, negative,
227 U8 => [U8, U16, U32, U64, U128] => [],
228 U16 => [U16, U32, U64, U128] => [],
229 U32 => [U32, U64, U128] => [],
230 U64 => [U64, U128] => [],
231 U128 => [U128] => []),
236 fn lint_int_literal<'tcx>(
237 cx: &LateContext<'tcx>,
238 type_limits: &TypeLimits,
239 e: &'tcx hir::Expr<'tcx>,
244 let int_type = t.normalize(cx.sess().target.ptr_width);
245 let (min, max) = int_ty_range(int_type);
246 let max = max as u128;
247 let negative = type_limits.negated_expr_id == Some(e.hir_id);
249 // Detect literal value out of range [min, max] inclusive
250 // avoiding use of -min to prevent overflow/panic
251 if (negative && v > max + 1) || (!negative && v > max) {
252 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
253 report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
257 let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
258 if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
259 if let hir::ExprKind::Struct(..) = par_e.kind {
260 if is_range_literal(cx.sess().source_map(), par_e)
261 && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
263 // The overflowing literal lint was overridden.
269 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
270 lint.build(&format!("literal out of range for `{}`", t.name_str()))
272 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
275 .span_to_snippet(lit.span)
276 .expect("must get snippet from literal"),
286 fn lint_uint_literal<'tcx>(
287 cx: &LateContext<'tcx>,
288 e: &'tcx hir::Expr<'tcx>,
292 let uint_type = t.normalize(cx.sess().target.ptr_width);
293 let (min, max) = uint_ty_range(uint_type);
294 let lit_val: u128 = match lit.node {
295 // _v is u8, within range by definition
296 ast::LitKind::Byte(_v) => return,
297 ast::LitKind::Int(v, _) => v,
300 if lit_val < min || lit_val > max {
301 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
302 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
304 hir::ExprKind::Cast(..) => {
305 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind {
306 cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
307 lint.build("only `u8` can be cast into `char`")
310 &"use a `char` literal instead",
311 format!("'\\u{{{:X}}}'", lit_val),
312 Applicability::MachineApplicable,
319 hir::ExprKind::Struct(..) if is_range_literal(cx.sess().source_map(), par_e) => {
320 let t = t.name_str();
321 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
322 // The overflowing literal lint was overridden.
329 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
330 report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
333 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
334 lint.build(&format!("literal out of range for `{}`", t.name_str()))
336 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
339 .span_to_snippet(lit.span)
340 .expect("must get snippet from literal"),
350 fn lint_literal<'tcx>(
351 cx: &LateContext<'tcx>,
352 type_limits: &TypeLimits,
353 e: &'tcx hir::Expr<'tcx>,
356 match cx.typeck_results().node_type(e.hir_id).kind {
359 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
360 lint_int_literal(cx, type_limits, e, lit, t, v)
365 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
367 let is_infinite = match lit.node {
368 ast::LitKind::Float(v, _) => match t {
369 ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
370 ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
374 if is_infinite == Ok(true) {
375 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
376 lint.build(&format!("literal out of range for `{}`", t.name_str()))
378 "the literal `{}` does not fit into the type `{}` and will be converted to `std::{}::INFINITY`",
381 .span_to_snippet(lit.span)
382 .expect("must get snippet from literal"),
394 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
395 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
397 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
398 // propagate negation, if the negation itself isn't negated
399 if self.negated_expr_id != Some(e.hir_id) {
400 self.negated_expr_id = Some(expr.hir_id);
403 hir::ExprKind::Binary(binop, ref l, ref r) => {
404 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
405 cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
406 lint.build("comparison is useless due to type limits").emit()
410 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
414 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
416 hir::BinOpKind::Lt => v > min && v <= max,
417 hir::BinOpKind::Le => v >= min && v < max,
418 hir::BinOpKind::Gt => v >= min && v < max,
419 hir::BinOpKind::Ge => v > min && v <= max,
420 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
425 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
429 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
430 hir::BinOpKind::Le => hir::BinOpKind::Ge,
431 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
432 hir::BinOpKind::Ge => hir::BinOpKind::Le,
439 cx: &LateContext<'_>,
444 let (lit, expr, swap) = match (&l.kind, &r.kind) {
445 (&hir::ExprKind::Lit(_), _) => (l, r, true),
446 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
449 // Normalize the binop so that the literal is always on the RHS in
451 let norm_binop = if swap { rev_binop(binop) } else { binop };
452 match cx.typeck_results().node_type(expr.hir_id).kind {
454 let (min, max) = int_ty_range(int_ty);
455 let lit_val: i128 = match lit.kind {
456 hir::ExprKind::Lit(ref li) => match li.node {
459 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
465 is_valid(norm_binop, lit_val, min, max)
467 ty::Uint(uint_ty) => {
468 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
469 let lit_val: u128 = match lit.kind {
470 hir::ExprKind::Lit(ref li) => match li.node {
471 ast::LitKind::Int(v, _) => v,
476 is_valid(norm_binop, lit_val, min, max)
482 fn is_comparison(binop: hir::BinOp) -> bool {
489 | hir::BinOpKind::Gt => true,
499 "proper use of libc types in foreign modules"
502 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
505 IMPROPER_CTYPES_DEFINITIONS,
507 "proper use of libc types in foreign item definitions"
510 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
512 crate enum ImproperCTypesMode {
517 crate struct ImproperCTypesVisitor<'a, 'tcx> {
518 crate cx: &'a LateContext<'tcx>,
519 crate mode: ImproperCTypesMode,
522 enum FfiResult<'tcx> {
524 FfiPhantom(Ty<'tcx>),
525 FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option<String> },
528 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
529 /// Is type known to be non-null?
530 fn ty_is_known_nonnull(&self, ty: Ty<'tcx>) -> bool {
532 ty::FnPtr(_) => true,
535 if def.is_box() && matches!(self.mode, ImproperCTypesMode::Definitions) =>
539 ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
540 let guaranteed_nonnull_optimization = self
545 .any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed));
547 if guaranteed_nonnull_optimization {
551 for variant in &def.variants {
552 if let Some(field) = variant.transparent_newtype_field(self.cx.tcx) {
553 if self.ty_is_known_nonnull(field.ty(self.cx.tcx, substs)) {
565 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If
566 /// the type is it is, return the known non-null field type, else None. Currently restricted
567 /// to function pointers, boxes, references, `core::num::NonZero*`, `core::ptr::NonNull`, and
568 /// `#[repr(transparent)]` newtypes.
569 crate fn is_repr_nullable_ptr(
572 ty_def: &'tcx ty::AdtDef,
573 substs: SubstsRef<'tcx>,
574 ) -> Option<Ty<'tcx>> {
575 if ty_def.variants.len() != 2 {
579 let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
580 let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
581 let fields = if variant_fields[0].is_empty() {
583 } else if variant_fields[1].is_empty() {
589 if fields.len() != 1 {
593 let field_ty = fields[0].ty(self.cx.tcx, substs);
594 if !self.ty_is_known_nonnull(field_ty) {
598 // At this point, the field's type is known to be nonnull and the parent enum is
599 // Option-like. If the computed size for the field and the enum are different, the non-null
600 // optimization isn't being applied (and we've got a problem somewhere).
601 let compute_size_skeleton =
602 |t| SizeSkeleton::compute(t, self.cx.tcx, self.cx.param_env).unwrap();
603 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
604 bug!("improper_ctypes: Option nonnull optimization not applied?");
610 /// Check if the type is array and emit an unsafe type lint.
611 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
612 if let ty::Array(..) = ty.kind {
613 self.emit_ffi_unsafe_type_lint(
616 "passing raw arrays by value is not FFI-safe",
617 Some("consider passing a pointer to the array"),
625 /// Checks if the given field's type is "ffi-safe".
626 fn check_field_type_for_ffi(
628 cache: &mut FxHashSet<Ty<'tcx>>,
629 field: &ty::FieldDef,
630 substs: SubstsRef<'tcx>,
631 ) -> FfiResult<'tcx> {
632 let field_ty = field.ty(self.cx.tcx, substs);
633 if field_ty.has_opaque_types() {
634 self.check_type_for_ffi(cache, field_ty)
636 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
637 self.check_type_for_ffi(cache, field_ty)
641 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
642 fn check_variant_for_ffi(
644 cache: &mut FxHashSet<Ty<'tcx>>,
647 variant: &ty::VariantDef,
648 substs: SubstsRef<'tcx>,
649 ) -> FfiResult<'tcx> {
652 if def.repr.transparent() {
653 // Can assume that only one field is not a ZST, so only check
654 // that field's type for FFI-safety.
655 if let Some(field) = variant.transparent_newtype_field(self.cx.tcx) {
656 self.check_field_type_for_ffi(cache, field, substs)
658 bug!("malformed transparent type");
661 // We can't completely trust repr(C) markings; make sure the fields are
663 let mut all_phantom = !variant.fields.is_empty();
664 for field in &variant.fields {
665 match self.check_field_type_for_ffi(cache, &field, substs) {
669 FfiPhantom(..) if def.is_enum() => {
672 reason: "this enum contains a PhantomData field".into(),
681 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
685 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
686 /// representation which can be exported to C code).
687 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
690 let cx = self.cx.tcx;
692 // Protect against infinite recursion, for example
693 // `struct S(*mut S);`.
694 // FIXME: A recursion limit is necessary as well, for irregular
696 if !cache.insert(ty) {
702 if def.is_box() && matches!(self.mode, ImproperCTypesMode::Definitions) =>
707 ty::Adt(def, substs) => {
708 if def.is_phantom_data() {
709 return FfiPhantom(ty);
711 match def.adt_kind() {
712 AdtKind::Struct | AdtKind::Union => {
713 let kind = if def.is_struct() { "struct" } else { "union" };
715 if !def.repr.c() && !def.repr.transparent() {
718 reason: format!("this {} has unspecified layout", kind),
720 "consider adding a `#[repr(C)]` or \
721 `#[repr(transparent)]` attribute to this {}",
727 let is_non_exhaustive =
728 def.non_enum_variant().is_field_list_non_exhaustive();
729 if is_non_exhaustive && !def.did.is_local() {
732 reason: format!("this {} is non-exhaustive", kind),
737 if def.non_enum_variant().fields.is_empty() {
740 reason: format!("this {} has no fields", kind),
741 help: Some(format!("consider adding a member to this {}", kind)),
745 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
748 if def.variants.is_empty() {
749 // Empty enums are okay... although sort of useless.
753 // Check for a repr() attribute to specify the size of the
755 if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
756 // Special-case types like `Option<extern fn()>`.
757 if self.is_repr_nullable_ptr(ty, def, substs).is_none() {
760 reason: "enum has no representation hint".into(),
762 "consider adding a `#[repr(C)]`, \
763 `#[repr(transparent)]`, or integer `#[repr(...)]` \
764 attribute to this enum"
771 if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
774 reason: "this enum is non-exhaustive".into(),
779 // Check the contained variants.
780 for variant in &def.variants {
781 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
782 if is_non_exhaustive && !variant.def_id.is_local() {
785 reason: "this enum has non-exhaustive variants".into(),
790 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
801 ty::Char => FfiUnsafe {
803 reason: "the `char` type has no C equivalent".into(),
804 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
807 ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
809 reason: "128-bit integers don't currently have a known stable ABI".into(),
813 // Primitive types with a stable representation.
814 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
816 ty::Slice(_) => FfiUnsafe {
818 reason: "slices have no C equivalent".into(),
819 help: Some("consider using a raw pointer instead".into()),
823 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
826 ty::Str => FfiUnsafe {
828 reason: "string slices have no C equivalent".into(),
829 help: Some("consider using `*const u8` and a length instead".into()),
832 ty::Tuple(..) => FfiUnsafe {
834 reason: "tuples have unspecified layout".into(),
835 help: Some("consider using a struct instead".into()),
838 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
840 matches!(self.mode, ImproperCTypesMode::Definitions)
841 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
847 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
848 self.check_type_for_ffi(cache, ty)
851 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
854 if self.is_internal_abi(sig.abi()) {
857 reason: "this function pointer has Rust-specific calling convention".into(),
859 "consider using an `extern fn(...) -> ...` \
860 function pointer instead"
866 let sig = cx.erase_late_bound_regions(&sig);
867 if !sig.output().is_unit() {
868 let r = self.check_type_for_ffi(cache, sig.output());
876 for arg in sig.inputs() {
877 let r = self.check_type_for_ffi(cache, arg);
888 ty::Foreign(..) => FfiSafe,
890 // While opaque types are checked for earlier, if a projection in a struct field
891 // normalizes to an opaque type, then it will reach this branch.
893 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
896 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
897 // so they are currently ignored for the purposes of this lint.
898 ty::Param(..) | ty::Projection(..)
899 if matches!(self.mode, ImproperCTypesMode::Definitions) =>
911 | ty::GeneratorWitness(..)
912 | ty::Placeholder(..)
913 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
917 fn emit_ffi_unsafe_type_lint(
924 let lint = match self.mode {
925 ImproperCTypesMode::Declarations => IMPROPER_CTYPES,
926 ImproperCTypesMode::Definitions => IMPROPER_CTYPES_DEFINITIONS,
929 self.cx.struct_span_lint(lint, sp, |lint| {
930 let item_description = match self.mode {
931 ImproperCTypesMode::Declarations => "block",
932 ImproperCTypesMode::Definitions => "fn",
934 let mut diag = lint.build(&format!(
935 "`extern` {} uses type `{}`, which is not FFI-safe",
938 diag.span_label(sp, "not FFI-safe");
939 if let Some(help) = help {
943 if let ty::Adt(def, _) = ty.kind {
944 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
945 diag.span_note(sp, "the type is defined here");
952 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
953 struct ProhibitOpaqueTypes<'a, 'tcx> {
954 cx: &'a LateContext<'tcx>,
955 ty: Option<Ty<'tcx>>,
958 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
959 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
965 // Consider opaque types within projections FFI-safe if they do not normalize
966 // to more opaque types.
967 ty::Projection(..) => {
968 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
970 // If `ty` is a opaque type directly then `super_visit_with` won't invoke
971 // this function again.
972 if ty.has_opaque_types() { self.visit_ty(ty) } else { false }
974 _ => ty.super_visit_with(self),
979 let mut visitor = ProhibitOpaqueTypes { cx: self.cx, ty: None };
980 ty.visit_with(&mut visitor);
981 if let Some(ty) = visitor.ty {
982 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
989 fn check_type_for_ffi_and_report_errors(
994 is_return_type: bool,
996 // We have to check for opaque types before `normalize_erasing_regions`,
997 // which will replace opaque types with their underlying concrete type.
998 if self.check_for_opaque_ty(sp, ty) {
999 // We've already emitted an error due to an opaque type.
1003 // it is only OK to use this function because extern fns cannot have
1004 // any generic types right now:
1005 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1007 // C doesn't really support passing arrays by value - the only way to pass an array by value
1008 // is through a struct. So, first test that the top level isn't an array, and then
1009 // recursively check the types inside.
1010 if !is_static && self.check_for_array_ty(sp, ty) {
1014 // Don't report FFI errors for unit return types. This check exists here, and not in
1015 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1017 if is_return_type && ty.is_unit() {
1021 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1022 FfiResult::FfiSafe => {}
1023 FfiResult::FfiPhantom(ty) => {
1024 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1026 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1027 // argument, which after substitution, is `()`, then this branch can be hit.
1028 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => return,
1029 FfiResult::FfiUnsafe { ty, reason, help } => {
1030 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1035 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1036 let def_id = self.cx.tcx.hir().local_def_id(id);
1037 let sig = self.cx.tcx.fn_sig(def_id);
1038 let sig = self.cx.tcx.erase_late_bound_regions(&sig);
1040 for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
1041 self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false);
1044 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1045 let ret_ty = sig.output();
1046 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1050 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1051 let def_id = self.cx.tcx.hir().local_def_id(id);
1052 let ty = self.cx.tcx.type_of(def_id);
1053 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1056 fn is_internal_abi(&self, abi: Abi) -> bool {
1057 if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
1065 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1066 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1067 let mut vis = ImproperCTypesVisitor { cx, mode: ImproperCTypesMode::Declarations };
1068 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
1070 if !vis.is_internal_abi(abi) {
1072 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1073 vis.check_foreign_fn(it.hir_id, decl);
1075 hir::ForeignItemKind::Static(ref ty, _) => {
1076 vis.check_foreign_static(it.hir_id, ty.span);
1078 hir::ForeignItemKind::Type => (),
1084 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1087 cx: &LateContext<'tcx>,
1088 kind: hir::intravisit::FnKind<'tcx>,
1089 decl: &'tcx hir::FnDecl<'_>,
1090 _: &'tcx hir::Body<'_>,
1094 use hir::intravisit::FnKind;
1096 let abi = match kind {
1097 FnKind::ItemFn(_, _, header, ..) => header.abi,
1098 FnKind::Method(_, sig, ..) => sig.header.abi,
1102 let mut vis = ImproperCTypesVisitor { cx, mode: ImproperCTypesMode::Definitions };
1103 if !vis.is_internal_abi(abi) {
1104 vis.check_foreign_fn(hir_id, decl);
1109 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1111 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1112 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1113 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1114 let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1115 let t = cx.tcx.type_of(item_def_id);
1116 let ty = cx.tcx.erase_regions(&t);
1117 let layout = match cx.layout_of(ty) {
1118 Ok(layout) => layout,
1120 ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
1123 let (variants, tag) = match layout.variants {
1124 Variants::Multiple {
1125 tag_encoding: TagEncoding::Direct,
1129 } => (variants, tag),
1133 let tag_size = tag.value.size(&cx.tcx).bytes();
1136 "enum `{}` is {} bytes large with layout:\n{:#?}",
1138 layout.size.bytes(),
1142 let (largest, slargest, largest_index) = enum_definition
1146 .map(|(variant, variant_layout)| {
1147 // Subtract the size of the enum tag.
1148 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1150 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1154 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1157 } else if size > s {
1164 // We only warn if the largest variant is at least thrice as large as
1165 // the second-largest.
1166 if largest > slargest * 3 && slargest > 0 {
1167 cx.struct_span_lint(
1168 VARIANT_SIZE_DIFFERENCES,
1169 enum_definition.variants[largest_index].span,
1171 lint.build(&format!(
1172 "enum variant is more than three times \
1173 larger ({} bytes) than the next largest",